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Vol. 38, 2016 DOI: 10.1093/epirev/mxv008 Advance Access publication: February 11, 2016

The Relationship Between Controlled Substances and Violence

Emma E. McGinty*, Seema Choksy, and Garen J. Wintemute * Correspondence to Dr. Emma E. McGinty, Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health, 624 North Broadway, Room 359, Baltimore, MD 21217 (e-mail: [email protected]).

Accepted for publication August 14, 2015.

controlled substances; drug trafficking; firearms; homicide; street drugs; violence

individuals who are “unlawful users of or addicted to any controlled substance” from purchasing or possessing firearms (10). However, the law does not clearly define “unlawful users,” and in recent years stakeholders have called for revision and clarification of this policy (11–13). The changing landscape of drug control policy in the United States, where recreational marijuana use is now legal in multiple states but still prohibited under federal law, suggests that a nuanced approach to revisiting this prohibition is needed. The ongoing policy debate surrounding this provision should be informed by the research evidence, but to date no comprehensive review of the epidemiologic relationship between controlled substances and firearm violence (and the implications of that relationship for policy) has been conducted. The initial goal of this review was to summarize the best available evidence on the relationship between controlled substance and firearm violence. However, we identified only 1 study meeting our inclusion criteria that was specific to violence committed with firearms. We therefore reviewed studies of this relationship using broader measures of interpersonal

INTRODUCTION

Since the late 1990s, the United States has directed billions of dollars toward efforts to prevent trafficking, use, and abuse of controlled substances, such as cocaine, heroin, methamphetamine, and marijuana. A key motivator of the “war on drugs” is concern that controlled substances are associated with heightened risk of violence, particularly firearm violence (1, 2). In the United States, the crack cocaine epidemic of the 1980s and 1990s was widely perceived as an important driver of elevated rates of firearm violence during that period (3) and, over the past 4 decades, drug-related violence perpetrated by gangs and cartels has been widely reported (4–6). Although public attention has focused predominantly on interpersonal violence, the majority of firearm deaths (60% in 2013) in the United States are suicides (7), and prior research suggests that controlled substance use may elevate risk of suicide as well as homicide (8, 9). The perceived connection between controlled substances and firearm violence is evident in federal law, which prohibits 5

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A causal relationship between controlled substances and firearm violence has been widely assumed in the United States, and federal law prohibits individuals who are “unlawful users of or addicted to any controlled substance” from purchasing or possessing firearms (68 FR 3750. 2003. Codified at 27 CFR §478.11). However, the law does a poor job of defining “unlawful users,” resulting in recent calls for a revised, actionable definition. Such a definition should be informed by research evidence, but to date the epidemiologic research on the relationship between controlled substances and violence has not been comprehensively reviewed. The initial goal of this review was to summarize the best available evidence on the relationship between controlled substances and firearm violence, but only 1 study specific to firearm violence was identified. We therefore reviewed studies of this relationship using broader measures of interpersonal violence and suicide, all of which included but were not limited to firearm violence, and measures of illicit firearm carrying. Prospective longitudinal studies (n = 22) from 1990 to 2014 were identified by using searches of online databases and citation tracking. Information was extracted from each study by using a standardized protocol. Quality of evidence was independently assessed by 2 reviewers. Aggregate measures of controlled substance use were associated with increased interpersonal violence and suicide, but evidence regarding the relationship between specific substances and violence was mixed. Involvement in illegal drug sales was consistently associated with interpersonal violence. To effectively revise extant federal law and delineate appropriate prohibiting criteria, more research is needed to understand the relationship between controlled substances and firearm violence.

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Prevalence of controlled substance use

Compared with the general population, both homicide offenders and suicide victims are more likely to use controlled substances (Figure 1). In the overall US population in 2013, an estimated 9% of Americans aged 12 years or older used any controlled substances in the past month (27). The most common illicit substance, marijuana, was used by 7.5% of Americans, followed by nonmedical use of prescription drugs

such as opioid analgesics, tranquilizers, and sedatives (2.5%); cocaine (0.6%); hallucinogens such as lysergic acid diethylamide (LSD), phencyclidine, and ecstasy (0.5%); methamphetamine (0.2%); and heroin (0.1%) (27). By contrast, in a 2004 survey of US state and federal prisoners, 24% of federal inmates and 28% of state inmates incarcerated for violent crimes reported being under the influence of 1 or more controlled substances at the time of the crime, and about 50% of both groups reported using controlled substances in the month prior to committing the violent offense that led to their incarceration (28). In a 2010 toxicology study of suicide victims in 16 US states, 17% of suicide victims tested positive for amphetamines, cocaine, marijuana, and/or opiates. Within specific categories, 3% tested positive for amphetamines, 5% for cocaine, 10% for marijuana, and 20% for opiates (29). Firearm violence in the United States

In 2013, there were 33,636 firearm deaths in the United States. Of these, 11,208 were homicides (33%) and 21,175 were suicides. The remaining 1,253 deaths were unintentional shootings, related to legal intervention, or of undetermined intent (7). Another 80,000 or more individuals are nonfatally wounded with firearms each year (30). High rates of firearm ownership in the United States are associated with rates of firearm morbidity and mortality that are considerably higher than in other high-income nations (31). Relationships between controlled substances and interpersonal violence

% Using Controlled Substances

In 1989, Goldstein et al. (32) first published their tripartite conceptual framework (Table 1), which theorized 3 pathways by which controlled substances lead to interpersonal violence:

30 25 20 15 10 5 0 Overall

State Prisoners

Federal Prisoners

Suicide Victims

Population

Figure 1. Controlled substance use showing overall population, perpetrators of violent crime, and suicide victims, United States, 2004– 2014. Figure 1 illustrates percent of the population using controlled substances in the overall US population and among state prisoners convicted of violent crimes, federal prisoners convicted of violent crimes, and suicide victims. Controlled substance use in the overall US population was measured as self-reported past-month use; controlled substance use in state and federal prisoners convicted of violent crime was measured as self-reported use at the time of the crime; and controlled substance use in suicide victims was measured by using toxicity screens (27–29).

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violence and suicide, all of which included but were not limited to firearm violence. We also included studies measuring the relationship between controlled substances and illicit firearm carrying, a precursor to interpersonal violence (14). The lack of firearm-specific studies is a key limitation of our review. Nonetheless, understanding the best available evidence on the relationship between controlled substances and measures of violence that include but are not limited to firearm violence can provide important insights into the role of illicit drugs in firearm violence and the implications for policy. The majority of risk factors for firearm and nonfirearm violence overlap (15, 16). There is therefore no strong theoretical reason to hypothesize that individuals’ involvement with controlled substances would be associated with elevated risk for nonfirearm violence but not firearm violence, or vice versa, unless demand for and access to firearms were very low or nonexistent among controlled substance users. Prior literature suggests that this is not the case: Rather, studies show that rates of firearm possession and carrying among US drug users are similar to or higher than rates among non-drug users, depending upon the specific study population (4, 17–21). Importantly, some measures of controlled substance involvement—for example, drug dealing or crack cocaine use—may be associated with higher demand for and access to firearms, and therefore higher risk of firearm violence, than others (e.g., recreational marijuana use) (4, 17, 18, 20, 22), and these relationships may differ for interpersonal violence versus suicide. Prior research has shown that nonfirearm violent acts, such as assault, are predictors of future interpersonal firearm violence (23, 24). Thus, studies assessing the relationship between controlled substances and serious violence generally, while not firearm specific, are measuring an outcome known to be directly related to firearm violence. Lack of firearm-specific studies is not unique to the controlled substances and violence literature. The best available epidemiologic research on the relationship between mental illness and interpersonal violence also uses measures of violence that include but are not limited to firearm incidents (25). Nonetheless, this research has informed the development and implementation of recent evidence-based firearm policies (11, 12, 25, 26). We could usefully take a similar approach in the case of drugs and firearm violence, where the active policy discussion is largely uninformed by research evidence. We begin by briefly summarizing rates of controlled substance use and firearm violence in the United States and discussing the pathways by which controlled substances might influence violence. We then describe the methods and results of our comprehensive review and conclude with discussion of research gaps and implications for firearm policy in the United States.

Controlled Substances and Violence

Table 1. Goldstein et al.’s Tripartite Framework for Pathways by Which Controlled Substances May Influence Perpetration of Violence Toward Others (32) Pathways by Which Controlled Substances May Influence Violence

Definition

Pathway 1 (psychopharmacological)

Physical and psychological effects of controlled substances on violence

Pathway 2 (economic compulsive)

Violence as the means for financing illicit drug use (e.g., assault in the course of robbery)

Pathway 3 (systemic)

Violence arising from disputes within illegal drug markets

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open to multiple threats to validity that preclude assessment of a causal association between controlled substances and violence perpetration. For example, retrospective and crosssectional studies make it difficult or impossible to establish temporality of involvement with controlled substances and violence, which is particularly problematic in the context of prior studies suggesting that antisocial and violent behavior can be risk factors for future drug use (46). To truly measure the association between controlled substances and violence toward others, it is critical to establish that individuals’ involvement with illicit drugs occurred prior to violence perpetration. It is also important to measure and establish the temporality of other factors associated with controlled substance use and violence, including but not limited to low socioeconomic status, delinquent peer groups, alcohol use and abuse, and history of violent or aggressive behavior. Although many cross-sectional studies measure the presence of these potentially confounding or mediating factors, they cannot establish temporality. For these reasons, in our review we include only prospective longitudinal studies of the relationship between controlled substances and interpersonal violence. Relationship between controlled substances and suicide

Unlike the relationship between controlled substances and interpersonal violence, which has received considerable attention in the past 4 decades from researchers, policymakers, and the public, the relationship between illicit drugs and suicide has received relatively little attention. As with perpetration of violence toward others, some evidence suggests that the physical and psychological effects of using some controlled substances, particularly increased impulsivity, may heighten risk of suicide (47, 48). To our knowledge, however, no theoretical frameworks comparable to the paradigm of Goldstein et al. have been developed to explain the relationship between controlled substances and suicidal behavior. Models of suicide risk often conceptualize 2 separate, although sometimes interrelated, causal pathways: the distal risk pathway and the proximal risk pathway (47). Proximal risk factors are those present in the hours and minutes leading up to suicidal behavior. For example, acute intoxication and access to a firearm during the short period when an individual is considering suicide are proximal risk factors. In contrast, distal risk factors are those that increase suicide risk over a longer period of time (47). For the purposes of this review, we examine the distal relationship between controlled substance use and suicide, for 3 reasons. First, it is difficult to disentangle the role of proximal substance use as a risk factor versus suicide attempt mechanism. Second, the distal pathway is conceptually similar to Goldstein et al.’s psychopharmacological pathway, allowing us to compare the evidence related to this pathway for interpersonal violence versus suicide. Third, because of the potential for early identification and amelioration, the distal pathway is more relevant for policy intervention. Some suicide and interpersonal risk factors overlap, and others are distinct. Despite its apparent role in several recent mass shootings and large amounts of public attention to the issue, mental illness is only rarely the direct cause of interpersonal

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the psychopharmacological, economic compulsive, and systemic pathways. On the psychopharmacological pathway, the physical and psychological effects of controlled substances, such as agitation, aggression, and cognitive impairment, heighten risk for violent behavior and impair the decision-making and communication skills necessary to avoid violence. On the economic compulsive pathway, controlled substances are related to violence when addicts turn to armed robbery or other violent crimes in order to finance their drug use. On the systemic pathway, disputes within illegal drug markets (e.g., conflicts over turf ) lead to violence. To begin to test his framework, Goldstein et al. (32) examined the causes of drug-related homicides committed in New York City in 1988 in the midst of that city’s crack cocaine epidemic. They worked with law enforcement to identify drug-related homicides (68% of which involved the use of firearms) and, based on detailed information collected about each case, to classify the homicide as most likely related to the psychopharmacological, economic compulsive, or systemic pathway to violence. A total of 218 drug-related homicides were identified (32). Of these, 14% were classified as psychopharmacological, 4% as economic compulsive, 75% as systemic, and 7% as multidimensional (32). The most frequently involved drug in all cases was crack cocaine, followed by powder cocaine, marijuana, and heroin (32). Alcohol was also involved in a high proportion of the homicides determined to fall along the psychopharmacological pathway (32). Our review of studies of the relationship between controlled substances and interpersonal violence is guided by the paradigm of Goldstein et al. In recent years, this framework has been critiqued and expanded upon but nonetheless remains the predominant paradigm guiding research on the causal relationship between illicit drugs and interpersonal violence (33). Although other paradigms such as opportunity theory and strain theory have provided important insights into the broader causes of interpersonal violence (34–36), to our knowledge the tripartite framework of Goldstein et al. is the only theory specific to controlled substances. Since the seminal work by Goldstein et al. in the late 1980s, multiple studies have attempted to examine the relationship between controlled substances and violence. Many of these studies are retrospective and/or cross-sectional (37–45). Although such studies can yield useful descriptive information, they are

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METHODS Search strategy

We identified peer-reviewed original research studies published in English-language sources between January 1, 1980, and December 31, 2014, using the online databases PubMed, Embase, and Web of Science. The search terms used to identify relevant articles included keywords related to controlled substances, firearms, interpersonal violence, and suicide. The full set of Boolean search terms was as follows: “drug” [tiab] or “controlled substance” [tiab] or “illicit substance” [tiab] or “narcotic” [tiab] or “stimulant” [tiab] or “hallucinogen” [tiab] or “depressant” [tiab] or “anabolic steroid” [tiab] or “marijuana” [tiab] or “heroin” [tiab] or “opioid” [tiab] or “opiate” [tiab] or “cocaine” [tiab] or “amphetamine” [tiab] or “methamphetamine” [tiab] or “barbiturate” [tiab] or “benzodiazepine” [tiab] or “inhalant” [tiab] AND “violence” [ti] or “violent” [ti] or “homicide” [ti] or “assault” [ti] or “suicide” [ti] or “aggress*” [ti] or “gun” [ti] or “firearm” [ti], where [ti] and [tiab] are the search tags for title and title and abstract, respectively. To identify articles that may have been missed by our electronic search, we also hand-searched the reference lists of 14 relevant review articles published between 1980 and 2014 (8, 9, 37–40, 43–45, 47, 52–55). To narrow the initial search return, the lead author (E.E.M.) screened the titles and abstracts returned by the initial search. The first and second authors (E.E.M. and S.C.) then screened the remaining full-text articles for eligibility. Study selection Inclusion criteria. We included studies meeting the following inclusion criteria: 1) prospective longitudinal design measuring the association between controlled substance use/ involvement (e.g., selling) and violence toward others or suicide; 2) use of a non-drug user comparison group selected

from the same cohort as the drug-user group; 3) publication in the peer-reviewed literature between 1980 and 2014; and 4) inclusion of at least 100 study participants. We defined prospective longitudinal studies as those that measured controlled substance use/involvement prior to measurement of violence. Studies that asked violent offenders about their drug use in the preceding days/weeks/months and attempted to estimate a longitudinal association in this manner were not included. We included studies measuring either aggregate use of controlled substances or use of 1 or more specific substances and placed no restrictions on the types of controlled substances measured, except for the exclusion related to infrequently misused prescription drugs described in the following paragraph. Although we used the tripartite framework of Goldstein et al. and the distal pathway model for suicide risk to guide the scope and organize the results of our review, our selection of studies was motivated primarily by the desire to capture the best available research designed to assess the causal relationship between controlled substances and violence. Thus, we included prospective longitudinal studies where clear temporality between controlled substance involvement and violence could be established. Exclusion criteria. We excluded studies on the basis of the following criteria: 1) used a retrospective or cross-sectional design; 2) measured the association between prescription drugs that are not frequently misused, for example, antiepileptics, antidepressants, and antipsychotics, with violence perpetration or suicide; 3) used nonhuman subjects; 4) measured only the combined association between alcohol and drugs with outcomes of interest; 5) examined the relationship between controlled substances and violent victimization, rather than perpetration or suicide; and 6) solely measured drug overdose as the method of suicide (only studies that examined controlled substance use as a risk factor preceding suicide were included). Data extraction

We used a structured instrument (Web Appendix available at http://aje.oxfordjournals.org/) to extract key information from articles. Development of the instrument was informed by the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist (56) and the Cochrane Handbook (57). Information extracted for each study included the following: title; authors; study objective; study design; study population, including inclusion and exclusion criteria; participant recruitment; study setting; data sources; method and timeframe of assessment; definitions of controlled substance and violence measures; covariates controlled for in final analytical model; and measure(s) of association between controlled substances and violence. For interpersonal violence, we classified measures of association as psychopharmacological, economic compulsive, or systemic. Measures testing the association between individual drug use and interpersonal violence outcomes except armed robbery were classified as psychopharmacological. Measures testing the association between index measures of economic compulsion and interpersonal violence and measures testing the association between individual drug use and robbery were classified as economic compulsive. Measures testing the association between Epidemiol Rev 2016;38:5–31

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violence: The best available research suggests that 3%–5% of all interpersonal violence in the United States is directly attributable to mental illness (25). In contrast, mental illness is strongly associated with risk of suicide (25). Mood disorders such as depression place individuals at particularly high risk of suicide (49), and these disorders often co-occur with use of controlled substances. In the United States in a given year, about 8% of individuals with any mood disorder also have a drug use disorder, compared with about 2% of the overall US population (50). Importantly, alcohol abuse, another risk factor for suicide, often co-occurs with both controlled substance use and mood disorders (50). As with interpersonal violence, use of controlled substances and suicide share many other risk factors, including personality traits such as impulsivity and hopelessness and situational factors such as stressful life circumstances related to poverty, unemployment, or divorce (47, 51). These factors may confound, mediate, or moderate the relationship between controlled substances and suicide (47). For the reasons given above, we limit our review of studies of the relationship between controlled substance use and suicide to prospective longitudinal studies.

Controlled Substances and Violence

involvement in drug sales and violence perpetration were classified as systemic. Measures of the relationship between controlled substances and suicide were not classified into separate subcategories. Initial data extraction was performed by S.C. and then verified by E.E.M. Study quality assessment

Data analysis

Because of the heterogeneity in study populations, measures, and analytical strategies used to assess the associations between controlled substances and violence perpetration and suicide, we did not attempt to conduct a meta-analysis and relied instead on a narrative synthesis. Results are summarized in Tables 2–5, which are organized by alphabetical order of author surnames and the text of the Results. RESULTS Study identification

The initial electronic search returned 2,921 unique articles. An additional 9 studies were identified through searches of the reference lists of review articles. Title and abstract screening identified 217 potentially relevant studies. After full-article review, 195 of these were excluded because of failure to meet the review’s inclusion criteria, for a final sample of 22 articles (Figure 2). Of these, 17 measured violence perpetration outcomes and 5 measured suicide outcomes (Table 2). Epidemiol Rev 2016;38:5–31

Across all studies, controlled substance measures included aggregate measures of any controlled substance use, use of individual drugs or drug classes (amphetamine/methamphetamine, barbiturates, cocaine, marijuana, opiates, phencyclidine/ hallucinogens, tranquilizers, prescription drugs, sedatives), sale of any illicit drug, sale of “hard drugs” excluding marijuana, and sale of marijuana. No studies meeting our inclusion criteria examined heroin use. Studies measured a range of violence outcomes, including index measures of violent behavior, assault, weapons offenses, homicide, and suicide. Study quality

No studies were determined to have low risk of bias, a classification Cochrane defines as comparable to a well-conducted randomized controlled trial (57). Eleven of the 22 studies had moderate risk of bias, and 11 studies had serious risk of bias (Table 2). No studies were scored as having critical risk. The most frequent threats to validity were failure to measure key confounders and selection into the study population based on drug use or violence. Interpersonal violence

The evidence on the relationship between measures of controlled substance use and interpersonal violence was mixed, with the highest quality studies that controlled for concurrent alcohol use tending to show no association. The evidence on the economic compulsive pathway was too limited to draw conclusions, and involvement with illegal drug sales (Goldstein et al.’s systemic pathway) was consistently associated with interpersonal violence. The psychopharmacological pathway between controlled substances and violence perpetration Aggregate measures. We extracted 7 such measures from 7 studies (59–65) (Table 3). Three studies showed a positive relationship between controlled substance use and interpersonal violence (59, 63, 65) and 4 showed no association (60–62, 64). Only 1 study measured a close temporal relationship between drug use and interpersonal violence; controlling for concurrent alcohol use, Mulvey et al. (62) found no association between prior-day use of controlled substances and subsequent commission of violent acts. All other studies in this category measured controlled substance use 1 year or more prior to measuring violence. The 3 studies showing a positive association between aggregate measures of controlled substance use and interpersonal violence had study periods of 5 years or longer. Brook et al. (59) measured controlled substance use and violent behavior in a cohort of New York City youth in 1990, 1994, 1999, and 2004. Self-reported past-year illicit drug use in 1994 was associated with increased likelihood of self-reported violent behavior in 1999 and 2004. In 2 studies of California continuation high school students, Sussman et al. (63) and Weiner et al. (65) found a positive relationship between drug use and subsequent violence perpetration. The 3 studies showing a positive association all had serious threat of bias and did not control for concurrent alcohol use.

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We used a modified version of the Cochrane risk of bias assessment tool for nonrandomized studies (ACROBATNRSI) (57) to grade the quality of each study included in our review (Web Table 1) (57). Because the Cochrane tool is designed to assess the quality of observational intervention studies and the literature we reviewed is epidemiologic rather than interventional, we modified the tool by excluding the checklist items relevant only for intervention studies. Fourteen quality criteria were assessed across 5 domains (confounding, bias in selection of participants into the study, bias due to missing data, bias in measurement of outcomes, and bias in selection of the reported result). For each domain, studies received a rating of low, moderate, serious, or critical risk of bias. Studies were then assigned an overall bias rating based on the domain-specific scores. The tool is designed so that only randomized controlled trials can receive an overall “low” bias rating. As no randomized controlled trials on the topic of interest exist, the highest rating a rigorous prospective longitudinal study could achieve was “moderate.” Following Cochrane conventions, studies receiving a “critical” bias score are not reviewed. Quality assessments were conducted independently by 2 authors (E.E.M. and S.C.), and interrater reliability for each item was assessed by using κ statistics. The majority of individual items and all overall bias judgments met conventional standards for reliability of 0.69 or higher (58). Three individual items had κ statistics between 62 and 68. In the case of discrepancy in the final bias rating, the 2 raters discussed disagreements and came to consensus.

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First Author, Year (Reference No.)

Years of Data Collection

Frequency of Data Collection

Study Population

Location

Study No.

Drugs/Violence Pathway Studied

Susceptibility to Bias (Low, Moderate, or Serious Risk)

Perpetration of Violence Toward Others Bellair, 2009 (75)

1997–2001

5 waves of data collection in 1997, 1998, 1999, 2000, and 2001

A nationally representative sample of youth aged 12–16 years in 1997

United States

5,567

Moderate

Brady, 2008 (71)

1996–2000

3 waves of data collection in 1996, 1999, and 2000

Youth aged 12–15 years insured by a large health maintenance organization

United States

302

Psychopharmacological

Serious

Brook, 2011 (59)

1990–2004

4 years of data collection at 5-year intervals: 1990, 1994, 1999, and 2004

Students in grades 7–10 (in 1990) in 11 schools

East Harlem, New York, New York

1,332

Psychopharmacological

Serious

Cerdá, 2010 (74)

1990–1999

10 years of data collection at 1-year intervals, 1990– 1999

Gun homicide victims from 1990 to 1999

New York, New York

8,820

Systemic

Moderate

Dembo, 1990 (69)

1986–1987

2 measures 6 months apart, exact timing unspecified

Youth aged 10–18 years admitted to a regional detention center

Tampa, Florida

201

Psychopharmacological, systemic

Serious

Ellickson, 2000 (70)

1985–1990

2 waves of data collection, 1985 and 1990

Seventh grade students (in 1985) from 30 schools

California and Oregon

4,390

Psychopharmacological

Moderate

Friedman, 2001 (66)

Years not given; 2.5-year period

2 measures during 2.5-year period, exact timing unspecified

Inner-city, low socioeconomic status African-American adults

Philadelphia, Pennsylvania

612

Psychopharmacological, economic compulsive, systemic

Moderate

Green, 2010 (68)

1966–2003

4 waves of data collection in 1966, 1975–1977, 1992– 1993, and 2002–2003

Community cohort of urban African Americans followed from age 6 to 42 years

Woodlawn, Chicago, Illinois

702

Psychopharmacological, systemic

Moderate

Kuhns, 2005 (60)

1976–1977

3 waves of data collection in 1976, 1977, and 1978

Representative sample of US youth aged 11–17 years in 1976

United States

1,725

Psychopharmacological

Moderate

McKetin, 2014 (67)

2006–2010

4 waves of data collection at baseline, 3 months after baseline, 1 year after baseline, and 3 years after baseline

Methamphetamine-dependent individuals aged ≥16 years

Sydney and Brisbane, Australia

278

Psychopharmacological

Serious

Menard, 2001 (61)

1976–1992

9 waves of data collection in 1976, 1977, 1978, 1979, 1980, 1983, 1986, 1989, and 1992

A representative sample of adolescents aged 11–17 years in 1976 and 22–33 years in 1992

United States

1,725

Psychopharmacological, systemic

Serious

Mulvey, 2006 (62)

Year not reported

26 weekly interviews, exact timing unspecified

Individuals identified as high risk for involvement in repeated violence in the emergency room of an urban psychiatric hospital

Northeastern United States

132

Psychopharmacological

Serious

Pedersen, 2010 (73)

1992–2005

4 waves of data collection at ages 13, 15, 20, and 27 years

Population-based sample of adolescents between 12 and 16 years of age in 1992

Norway

1,353

Psychopharmacological

Moderate

Sussman, 2004 (63)

1994–2000

2 waves of data collection in 1994–1995 and 1999– 2000

A representative sample of high school students

Five-county region in southern California

676

Psychopharmacological

Serious

Table continues

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Systemic

10 McGinty et al.

Table 2. Summary of Included Studies (n = 22), 1990–2014

First Author, Year (Reference No.)

Years of Data Collection

Frequency of Data Collection

Study Population

Study No.

Location

Van Dorn, 2012 (64)

2001–2005

Two waves of data collection in 2001–2002 and 2004– 2005

Nationally representative sample of the civilian noninstitutionalized adult population

United States

Wei, 2004 (72)

1991–2000

10 waves of data collection at ages 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 years

Males aged 11 (in 1991) with antisocial behavior participating in the Pittsburgh Youth Survey

Pittsburgh, Pennsylvania

Weiner, 2005 (65)

Years not reported; 5-year study period

2 waves of data collection at baseline and an average of 5 years after baseline

Continuation (alternative) of high school students

21 districts in southern California

Drugs/Violence Pathway Studied

Susceptibility to Bias (Low, Moderate, or Serious Risk)

34,653

Psychopharmacological

Moderate

503

Psychopharmacological

Serious

1,867

Psychopharmacological, economic compulsive

Serious

Suicide 1969–1983

Baseline data collected at conscription in 1969 were linked to inpatient registry data; all inpatient hospitalizations from 1969 to 1983 were measured

Men conscripted for military training in 1969–1970

Sweden

50,465

Psychopharmacological

Serious

Allgulander, 1992 (80)

1973–1987

Used inpatient and suicide registry data; all relevant records between 1973 and 1987 were measured

Patients discharged with at least 1 psychiatric diagnosis from inpatient hospitals

Stockholm County, Sweden

80,970

Psychopharmacological

Moderate

Nilsson, 2014 (78)

1999–2008

Used homeless registry, civil registration system, psychiatric central registry, and cause of death registry data. All relevant records between 1999 and 2008 were measured

Individuals aged ≥16 years with at least 1 contact with a homeless shelter during the study period

Denmark

32,010

Psychopharmacological

Moderate

Petronis, 1990 (79)

1984–1985

Two waves of data collection in 1984 and 1985

ECA participants

Five US cities: New Haven, Connecticut; Baltimore, Maryland; St. Louis, Missouri; Durham, North Carolina; and Los Angeles, California

13,673

Psychopharmacological

Moderate

Yen, 2003 (76)

Years not reported; 2-year study period

Four waves of data collection at baseline, 6 months after baseline, 1 year after baseline, and 2 years after baseline

Individuals aged 18–45 years with diagnosed personality disorders recruited from treatment clinics

Four CLPS sites

621

Psychopharmacological

Serious

Abbreviations: CLPS, Collaborative Longitudinal Personality Disorders Study; ECA, Epidemiologic Catchment Area referring to 5 cities in the United States: New Haven, Connecticut; Baltimore, Maryland; St. Louis, Missouri; Durham, North Carolina; and Los Angeles, California.

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Allebeck, 1990 (77)

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Table 2. Continued

First Author, Year (Reference No.)

Controlled Substance Measure

Violence Measure

Brook, 2011 (59)

Self-reported past year illicit drug use

Serious violence scale. Individual items comprising the scale assessed frequency threatening with a weapon; shooting at or hitting with a weapon; cutting with a knife; and beating up/throwing something at someone else

Illegal drug use in 1994 was associated with violent behavior in 1999 (coefficient = 0.08, t statistic = 2.02) and 2004 (coefficient = 0.12, t statistic = 3.67)

Ethnicity, sex

Positive

Kuhns, 2005 (60)

Frequency of drug use, including marijuana, cocaine, heroin, barbiturates, amphetamines, and hallucinogens

Serious violence offending, defined by using the Crimes Against Persons Scale

Drug use in wave 1 of the survey was not associated with increased odds of serious violence offending at wave 2 (odds ratio = 0.05; P > 0.05). Drug use in wave 2 of the survey was not associated with increased odds of serious violent offending at wave 3 (odds ratio = 4.92; P > 0.05)

Attitudes toward violence, exposure to delinquent peers, neighborhood problems, family attachment, perceived family importance, alcohol use, minor delinquency

No association

Menard, 2001 (61)

Self-reported use of hallucinogens, amphetamines, heroin, cocaine, and barbiturates in the last calendar year

“Index violence,” defined as felony assault or robbery

Drug use had no association with violence

None

No association

Mulvey, 2006 (62)

Self-reported daily and weekly use of drugs excluding marijuana

Self-reported daily and weekly frequency of 9 aggressive acts, including pushing, hitting, and using a weapon

Drug use had no association with violence (odds ratio = 1.5, 95% CI: 0.8, 2.8)

Marijuana use and sales, alcohol use and sales, hard drug sales

No association

Sussman, 2004 (63)

Self-reported current use and frequency of use of “hard drugs” including cocaine, hallucinogens, stimulants, inhalants, PCP, heroin, and steroids

Violent behavior using a 4-item index adapted from the 1981 Monitoring the Future Survey

Current hard drug use was associated with violence perpetration (F statistic = 8.7; P < 0.05)

Baseline perpetration of violence, sex, beliefs about violence, and the acceptability and morality of drug use, self-identification with a high-risk group, and perceived stress

Positive

Van Dorn, 2012 (64)

Current (at baseline) drug abuse and/or dependence, measured using a structured interview schedule

Any violence, defined as any of the following having occurred in the time since the prior interview (≈2 years): 1) using a weapon like a stick, knife, or gun in a fight; 2) hitting someone so hard you injured them or they had to see a doctor; 3) starting a fire on purpose to destroy someone’s property or just to see it burn; 4) force someone to have sex against their will; 5) getting into a physical fight when or right after drinking; 6) getting into a fight when under the influence of a drug; 7) physically hurting another person in any way on purpose; 8) getting into a fight that came to swapping blows with someone like a husband, wife, boyfriend, or girlfriend; 9) getting into a lot of fights that you started

Drug use disorder had no association with violence (odds ratio = 1.51, 95% CI: 0.59, 3.84; P > 0.05)

Length of time between waves 1 and 2, age, sex, race, education, income, marital status, urban/rural, household size, history of abuse or neglect, mental illness and alcohol use disorders, stressful life circumstances

No association

Weiner, 2005 (65)

Self-reported monthly frequency of marijuana, cocaine, hallucinogen, stimulant, inhalant, and other drug use

Violence perpetration scale comprising items assessing the annual frequency of incidents in which a weapon was used to injure or threaten someone; injury was perpetrated without a weapon; and property was damaged or stolen on purpose. Adapted from the 1981 Monitoring the Future Survey

Illegal drug use was associated with increased likelihood of violence perpetration 5 years later (coefficient = 0.15, SE, 0.04; P < 0.05)

Sex and ethnicity, baseline level of violence perpetration

Positive

Covariates Accounted for in Analysis

Key Finding

Association Between Drugs and Violence

Aggregate Measures of Controlled Substance Use a

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12 McGinty et al.

Table 3. Summary of Results for Studies of the Psychopharmacological Relationship Between Controlled Substance Use and Violence Perpetration, 1990–2014

First Author, Year (Reference No.)

Controlled Substance Measure

Friedman, 2001 (66)

Self-reported frequency of use of amphetamines

Violence Measure

Key Finding

Covariates Accounted for in Analysis

Association Between Drugs and Violence

Amphetamines and Methamphetamines Self-reported conviction for assault

Amphetamine use had no association with assault conviction (P > 0.05)

Self-reported conviction for weapons offenses

Amphetamine use had no association with conviction for weapons offenses (P > 0.05)

No association

Self-reported conviction for attempted homicide

Amphetamine use had no association with attempted homicide conviction (P > 0.05)

No association

Self-reported conviction for homicide

Amphetamine use had no association with homicide conviction (P > 0.05)

No association

Self-reported gang drug-war fighting

Amphetamine use was associated with increased likelihood of gang drug-war fighting (partial correlation coefficient = 0.1; P < 0.05)

Positive

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

Compared with individuals with no methamphetamine use in the past month, individuals with 1–15 days of use (odds ratio = 2.8, 95% CI: 1.6, 4.9) and ≥16 days of use (odds ratio = 9.5, 95% CI: 4.80, 19.1) had increased odds of acting violently

No association

McKetin, 2014 (67)

Days of methamphetamine use in past 4 weeks

Violent behavior defined as history of assault with no physical harm, destruction of property, attack of others with intention to harm, or commission of actual physical harm (e.g., with a weapon)

Friedman, 2001 (66)

Self-reported frequency of use of barbiturates

Self-reported conviction for assault

Barbiturate use was associated with decreased likelihood of assault conviction (partial correlation coefficient = −0.1; P < 0.05)

Self-reported conviction for weapons offenses

Barbiturate use had no association with conviction for weapons offenses (P > 0.05)

No association

Self-reported conviction for attempted homicide

Barbiturate use was associated with decreased likelihood of attempted homicide conviction (partial correlation coefficient = −0.13; P < 0.05)

Negative

Self-reported conviction for homicide

Barbiturate use had no association with homicide conviction (P > 0.05)

No association

Self-reported gang drug-war fighting

Barbiturate use was associated with decreased likelihood of gang drug-war fighting (partial correlation coefficient = −0.33; P < 0.05)

Negative

Psychotic symptoms, other substance use (including drugs and alcohol), and sociodemographic characteristics

Positive

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

Negative

Barbiturates

Controlled Substances and Violence 13

Table continues

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Table 3. Continued

First Author, Year (Reference No.)

Controlled Substance Measure

Violence Measure

Key Finding

Covariates Accounted for in Analysis

Association Between Drugs and Violence

Cocaine Dembo, 1990 (69)

Cocaine (crack and powdered) use and frequency of use, measured by urinalysis and self-report

Crimes against persons, defined as self-reported aggravated assault, gang fights, hit a teacher/ student, committed sexual assault, strong-armed students/teachers/others

There was no association between cocaine use and crimes against persons

None, HIV risk

No association

Friedman, 2001 (66)

Self-reported frequency of use of cocaine/crack

Self-reported conviction for assault

Cocaine use had no association with assault conviction (P > 0.05)

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

No association

Self-reported conviction for weapons offenses

Cocaine use had no association with conviction for weapons offenses (P > 0.05)

No association

Self-reported conviction for attempted homicide

Cocaine use had no association with attempted homicide conviction (P > 0.05)

No association

Self-reported conviction for homicide

Cocaine use was associated with increased likelihood of homicide conviction (partial correlation coefficient = 0.14; P < 0.05)

Positive

Self-reported gang drug-war fighting

Cocaine use was associated with increased likelihood of gang drug-war fighting (partial correlation coefficient = 0.12; P < 0.05)

Positive

Marijuana Self-reported use of marijuana in past year

Self-reported minor or serious violence in the past year, ranging from starting a fight with other kids to firing a gun at another teenager

Marijuana use at age 15 years was associated with increased risk of violent perpetration at age 19 years (odds ratio = 2.90, 95% CI: 1.08, 7.82; P < 0.05). Marijuana use at age 18 years was not associated with violent perpetration at age 19 years (odds ratio = 1.66, 95% CI: 0.56, 4.90; P > 0.05)

Prior levels of violence involvement, age, sex, ethnicity, socioeconomic status

Mixed

Ellickson, 2000 (70)

Self-reported frequency of marijuana use in the past year

Predatory violence, defined as use of force to obtain money or things from people, involvement in gang fights, attacking someone with intent to injure or kill, and carrying a concealed weapon

Marijuana use was associated with increased odds of perpetration of predatory violence (odds ratio = 0.11; P < 0.05)

Alcohol use, school bonds, family bonds, problem behavior, peer drug use, drug offers, self-esteem, rebelliousness, age, sex, race, parent education, neighborhood socioeconomic status, school drug-use prevalence

Positive

Table continues

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Brady, 2008 (71)

14 McGinty et al.

Table 3. Continued

First Author, Year (Reference No.)

Controlled Substance Measure

Friedman, 2001 (66)

Self-reported frequency of use of marijuana

Violence Measure

Covariates Accounted for in Analysis

Key Finding

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

Association Between Drugs and Violence

Self-reported conviction for assault

Marijuana use had no association with assault conviction (P > 0.05)

Self-reported conviction for weapons offenses

Marijuana use was associated with increased likelihood of weapons offenses (partial correlation coefficient = 0.11; P < 0.05)

Positive

Self-reported conviction for attempted homicide

Marijuana use was associated with increased likelihood of attempted homicide (partial correlation coefficient = 0.10; P < 0.05)

Positive

Self-reported conviction for homicide

Marijuana use had no association with homicide conviction (P > 0.05)

No association

Self-reported gang drug-war fighting

Marijuana use had no association with gang drug-war fighting (P > 0.05)

No association

No association

Self-reported lifetime frequency of heavy marijuana use, defined as lifetime frequency of 20 or more times during adolescence

Violent crime, defined as murder, assault, battery, and domestic violence and obtained from law enforcement records

Heavy adolescent marijuana use had no association with violent crime (odds ratio = 1.09, 95% CI: 0.72, 1.65; P > 0.05)

Sex, socioeconomic status, family background, school adaptation, school achievement, tobacco smoking, and delinquency

No association

Menard, 2001 (61)

Self-reported use of marijuana, in the last calendar year

“Index violence,” defined as felony assault or robbery

Marijuana use was associated with violent crime (risk ratio = 2.60; P < 0.05)

None

Positive

Mulvey, 2006 (62)

Self-reported daily and weekly use of marijuana

Self-reported daily and weekly frequency of 9 aggressive acts, including pushing, hitting, and using a weapon

Prior-day marijuana use was associated with increased risk of violence (odds ratio = 1.6, 95% CI: 1.2, 2.0; P < 0.05)

Hard drug (nonmarijuana) use and sales, alcohol use and sales

Positive

Pedersen, 2010 (73)

Self-reported frequency of cannabis use in past 12 months

Serious crime including theft, robbery, and violence, as recorded by Statistics Norway

Marijuana use 1–10 times in the past year was not associated with serious crime (odds ratio = 1.6, 95% CI: 0.6, 4.7; P > 0.05) or ≥11 times in the past year (odds ratio = 1.4, 95% CI: 0.4, 5.2; P > 0.05)

Age, sex, parental cultural capital, parental monitoring, school grades, conduct problem, early adolescent marijuana use, cohabitation status, previous criminal charges, alcohol use, other illegal drug use

No association

Wei, 2004 (72)

Self-reported past-year frequency of use of marijuana, assessed by using the Substance Use Scale

Violence, defined by using a delinquency scale including items assessing self-reported past-year frequency of gang fighting, strong-arming, attacking someone with a weapon or intent to seriously hurt or kill, and rape or forced sex

Prior-year frequent marijuana use was associated with increased odds of violence among those aged 14 years (P < 0.05); 15 years (odds ratio = 3.07; P < 0.05); 16 years (odds ratio = 3.36; P < 0.05); 17 years (odds ratio = 2.67; P < 0.05); and 19 years (odds ratio = 3.83; P < 0.05). Prior-year frequent marijuana use was not associated with increased odds of violence among those aged 18 years or 20 years

Academic achievement, depressed mood, hyperactivity/ impulsivity/ inattention problems, poor communication with caretaker, poor supervision, caretaker perception of bad neighborhood, race/ethnicity

Mixed

Table continues

Controlled Substances and Violence 15

Green, 2010 (68)

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Table 3. Continued

First Author, Year (Reference No.)

Controlled Substance Measure

Violence Measure

Key Finding

Covariates Accounted for in Analysis

Association Between Drugs and Violence

Opiates b Friedman, 2001 (66)

Self-reported frequency of use of opiates

Self-reported conviction for assault

Opiate use was associated with increased likelihood of assault conviction (partial correlation coefficient = 0.14; P < 0.05)

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

Self-reported conviction for weapons offenses

Opiate use had no association with conviction for weapons offenses (P > 0.05)

No association

Self-reported conviction for attempted homicide

Opiate use was associated with increased likelihood of attempted homicide conviction (partial correlation coefficient = 0.11; P < 0.05)

Positive

Self-reported conviction for homicide

Opiate use had no association with homicide conviction (P > 0.05)

No association

Self-reported gang drug-war fighting

Opiate use was associated with increased likelihood of gang drug-war fighting (partial correlation coefficient = 0.36; P < 0.05)

Positive

Positive

PCP/Hallucinogens Self-reported frequency of use of PCP/hallucinogens

Epidemiol Rev 2016;38:5–31

Self-reported conviction for assault

PCP/hallucinogen use had no association with assault conviction (P > 0.05)

Self-reported conviction for weapons offenses

PCP/hallucinogen use had no association with conviction for weapons offenses (P > 0.05)

No association

Self-reported conviction for attempted homicide

PCP/hallucinogen use had no association with attempted homicide conviction (P > 0.05)

No association

Self-reported conviction for homicide

PCP/hallucinogen use had no association with attempted homicide conviction (P > 0.05)

No association

Self-reported gang drug-war fighting

PCP/hallucinogen use had no association with gang drug-war fighting conviction (P > 0.05)

No association

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

No association

Table continues

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Friedman, 2001 (66)

16 McGinty et al.

Table 3. Continued

First Author, Year (Reference No.)

Controlled Substance Measure

Friedman, 2001 (66)

Self-reported frequency of use of tranquilizers

Violence Measure

Key Finding

Covariates Accounted for in Analysis

Association Between Drugs and Violence

Tranquilizers Self-reported conviction for assault

Tranquilizer use was associated with increased likelihood of assault conviction (partial correlation coefficient = 0.11; P < 0.05)

Self-reported conviction for weapons offenses

Tranquilizer use had no association with conviction for weapons offenses (P > 0.05)

No association

Self-reported conviction for attempted homicide

Tranquilizer use had no association with attempted homicide conviction (P > 0.05)

No association

Self-reported conviction for homicide

Tranquilizer use had no association with homicide conviction (P > 0.05)

No association

Self-reported gang drug-war fighting

Tranquilizer use was associated with decreased likelihood of gang drug-war fighting (partial correlation coefficient = −0.007; P < 0.0.05)

Negative

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/hallucinogen use

Positive

Controlled Substances and Violence 17

Abbreviations: CI, confidence interval; HIV, human immunodeficiency virus; PCP, phencyclidine; SE, standard error. Studies in this category examined broad categories of controlled substance use, abuse, and addiction. Independent controlled substance variables in these studies included multiple specific substances. b Including heroin and other opiates. a

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Table 3. Continued

First Author, Year (Reference No.)

Association Between Drugs and Violence

Controlled Substance

Controlled Substance Measure

Weiner, 2005 (65)

Aggregate measures of controlled substance usea

Measure of economic compulsion, defined as mean responses of 4 items that assessed past-year frequency of taking/selling things to pay for alcohol or drugs; doing personal favors to get/pay for alcohol/drugs; sold personal belongings to pay for alcohol/drugs; done illegal things other than selling drugs to pay for alcohol/drugs

Violence perpetration scale comprising items assessing the annual frequency of incidents in which a weapon was used to injure or threaten someone; injury was perpetrated without a weapon; and property was damaged or stolen on purpose

Measures of economic compulsion were not associated with violence perpetration

>0.05

Sex, ethnicity, baseline level of violence perpetration

No association

Friedman, 2001 (66)

Amphetamines

Self-reported frequency of use of amphetamines

Self-reported conviction for robbery

Amphetamine use was associated with increased likelihood of robbery conviction (partial correlation coefficient = 0.21)

0.05

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/ hallucinogen use

No association

Friedman, 2001 (66)

Opiatesb

Self-reported frequency of use of opiates

Self-reported conviction for robbery

Opiate use was associated with increased likelihood of robbery conviction (partial correlation coefficient = 0.13)

0.05

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/ hallucinogen use

No association

Friedman, 2001 (66)

Tranquilizers

Self-reported frequency of use of tranquilizers

Self-reported conviction for robbery

Tranquilizer use had no association with robbery conviction

>0.05

Age, income, welfare status, head of household occupation, academic performance, school behavior, association with delinquent peers, adjustment, attitudes toward deviance, conduct disorder, antisocial personality, family problems and alcohol, marijuana, barbiturate, tranquilizer, cocaine/crack, heroin, opiate, PCP/ hallucinogen use

No association

Pathway 3 (Systemic Violence) Aggregate measures of sale of controlled substances

Self-reported sale of any illicit drug in the past 12 months

Violent acts, defined as self-report of attacking someone with intent to hurt them in the past year

Selling drugs was associated with increased risk of violence among non-gang members (incidence rate ratio = 1.1; P < 0.05) and gang members (incidence rate ratio = 2.0)