journal
of Substance
Abuse,
4,3 19-326
f 1992)
BRIEF REPORT
Patterns and Predictors of Simultaneous and Concurrent Use of Alcohol, Tobacco, Marijuana, and Hallucinogens in First-Year College Students Christopher S. Martin Western University
Psychiatric Institute and Clinic Department of Psychiatry of Pittsburgh School of Medicine
Patrick R. Clifford Rock 1. Clapper Center for Alcohol
and Addiction Studies Brown University
Polydrug use produces important health and safety risks. Little research has examined whether multiple drugs are used simultaneously (at the same time or in close temporal sequence). Instead, researchers have assessed concurrent polydrug use (the use of multiple drugs within a given time period such as years or months). The research here examined patterns and predictors of both simultaneous and concurrent polydrug use in 575 first-year college students. Both concurrent and simultaneous polydrug use were common for alcohol, tobacco, and marijuana. The percentage of concurrent polydrug users who were also simultaneous polydrug users ranged from 82% to 93% across subgroups defined by gender and the use of a single drug. Male gender, high levels of sensation seeking, and frequent alcohol use predicted single-drug versus polydrug use status as well as simultaneous polydrug use. Patterns and predictors of simultaneous and concurrent polydrug use should be addressed in prevention research and preventative interventions.
Polydrug use is a major health and safety concern, and is common among adolescent and young adult drug users. The comorbidity of alcohol and drug use diagnoses is increasingly recognized (American Psychiatric Association, 1987; DiFranza & Guerrera, 1990; Wilkinson, Leigh, Cordingley, Martin, 8c Lei, 1987). Research has examined predictors of polydrug use (Forney, Forney, & We thank David Lewis, Bruce Donovon, Toby Simon, Mary Grenedier. and Carol Cohen for their assistance in conducting this research. Parts of this report were presented at the annual meeting of the Research Society on Alcoholism, Marco Island, FL, June 8-13, 1991. Correspondence and requests for reprints should be sent to Christopher S. Martin, Western Psychiatric Institute and Clinic, Department of Psychiatry, University of Pittsburgh School of Medicine, 381 I O’Hara Street, Pittsburgh, PA 15213-2593. 319
C.S. Martin,
320
P.R. Clifford,
and R.L. Clapper
Ripley, 1989; Newcomb, Maddahian, & Bentler, 1986), and the order of initiation of use of multiple drugs (Kandel & Faust, 1975; Single, Kandel, 8c Faust, 1985). Use of more than one drug at the same time or in close temporal proximity has been termed simultaneous polydrug u.re (SPU; Grant & Harford, 1990). The use of more than one drug in the same time period (e.g., a year), but not necessarily at the same time, has been termed concurrent pofydrug use (CPU). Thus, SPU is a subset of CPU. Using data from a national sample, Grant and Harford reported CPU and SPU patterns for alcohol with sedatives and tranquilizers. A majority of concurrent users also were simultaneous users. Norton and Colliver (1988) reported data on combined use of marijuana and alcohol from a national sample. Combined use patterns were most common in persons aged 18-34. Most men (79%) and women (67%) who used alcohol and marijuana concurrently also used these drugs simultaneously. Aside from these reports, little is known about SPU patterns. Most research on polydrug use has not assessed whether multiple drugs were used in combination (i.e., simultaneously). Little is known about which drugs are and are not used in combination. Drug combinations can pose special health and safety risks (Abel & Dintcheff, 1986; Bo et al., 1975; Laisi, Linnoila, Seppala, Himberg, & Mattila, 1979; Sutton, 1983). For example, recent research indicates that simultaneous ingestion of alcohol and cocaine produces a novel stimulant compound cocaethylene (Jatlow, Elsworth, Bradberry, Winger, & Taylor, 199 l), which has a greater acute toxicity than does cocaine (Hearn, Rose, Wagner, Ciarleglio, & Mash, 1991). Therefore SPU data are vital for targeting relevant behaviors in prevention efforts. Researchers have not examined variables associated with SPU other than demographic characteristics. Previous research has found that personality characteristics related to disinhibition and sensation seeking are related to CPU (Andrucci, Archer, Pancoast, & Gordon, 1989; Jaffe & Archer, 1987; Zuckerman, 1979). Other research has linked concurrent drug use to age of first use of substances and peer use (Huba & Bentler, 1980; Stein, Newcomb, & Bentler, 1987). The association of personality and age of first use with SPU would suggest determinants of particular drug use patterns, and would identify high-risk subgroups for prevention efforts. The research here examined patterns and predictors of CPU and SPU in first-year college students. The proportion of concurrent and simultaneous users was calculated for the entire sample, and for different subgroups. The relative frequencies of different drug combinations were examined. Discriminant function analyses were used to examine variables that differentiated (1) single-drug users from polydrug users, and (2) polydrug users who did and did not engage in SPU. METHOD Subjects Subjects were 575 first-year students at a private university in New England. The mean age was 17.8 years (SD = 0.56). The sample comprised 42.7% of the
Simultaneous
and Concurrent
Use
321
entire first-year class. Fifty percent of the subjects were male, 4 1% were female, and 9% of the subjects left this item blank. The sample was 66.2% Caucasian, 12.9% Asian, 6.4% African-American, 4.5% Latino, and the remaining 10% of the subjects reported other ethnic identifications or left this item blank. Procedure Participation was voluntary and occurred at the beginning of the fall semester so that reports of past-year drug use would apply to senior year in high school and the following summer. Testing occurred during regularly scheduled student meetings, in groups of 10 to 50 students. Thirty of a total of 33 student groups were assessed. Although exact data were not available, approximately 2/9 of students attended these meetings, and of those, about 80% completed the questionnaire. An experimenter explained the purposes of the study and instructions on completing the questionnaire, and told subjects their responses would be confidential and anonymous. The experimenter remained in the room for the entire testing period and answered any questions. Questionnaire A multiple-choice questionnaire was developed for this project. Subjects reported age and gender and completed the Disinhibition, and the Thrill and Adventure Seeking subscales of the Sensation Seeking Scale (SSS; Zuckerman, 1979). Subjects reported past-year use of alcohol, tobacco, marijuana, hallucinogens, cocaine, and depressants. For each drug class, subjects reported age of first use and first intoxication, and the past-year average quantity and frequency of use. Quantity was defined as the amount used per occasion of use. Simultaneity was assessed by asking subjects about drugs used “at the same time.” Instructions read: “By ‘at the same time,’ we mean using another drug while you are still using or feeling the effects of the first drug.” Frequency questions were modeled after other self-report drug-taking measures (e.g., Cahalan, Cisin, & Crossley, 1969). Q uantity questions were worded as “Over the past year, when you used , how much, on the average, did you use?” A vocabulary was pilot tested for assessing the quantity of use of illicit drugs (Martin, Clapper, 8c Clifford, 199 1). Marijuana was assessed as the number of “hits/puffs,” cocaine as the number of “grams,” hallucinogens as the number of “hits” of LSD or “grams” of mushrooms and peyote. Subjects also reported the specific two-drug combinations that they used simultaneously in the past year. RESULTS Past-Year Use of the Six Drug Classes Polydrug use patterns are examined in the context of the past-year use of the different drug classes. Table 1 gives the percentage of subjects who reported use of four drug classes, and the average quantity and frequency of use among users.
322
C.S. Martin,
P.R. Clifford,
and
R.L. Clapper
Table 1. The Percentage of Subjects Who Reported Use of Alcohol, Tobacco, Marijuana, and Hallucinogens in the Past Year and Quantity and Frequency Among Users Past-Year Drug
Class
Alcohol Tobacco Marijuana Hallucinogens
Use
Average
Quantity’
(%I
M
(SD)
84.5 33.6 23.6 5.4
3.2 4.2 6.5 1.2
(2.10) (3.50) (3.50) (0.78)
Average
Frequencyh M (SD)
.80 I .60 .42 .16
(0.96) (2.50) (0.91) (0.29)
“Quantity was deftned as the amount used per occasion of use, and was measured as the number of “drinks” for alcohol, the number of “cigarettes” per day for tobacco, the number of “hits” or “puffs” for mariljuana, and the number of “hits” or “grams” for hallucinogens. “Frequency is expressed as the average number of days per week a given drug was used over the past year.
There was a substantial amount of past-year use of alcohol, tobacco, marijuana, and to a lesser extent, hallucinogens. Less than 2% of the sample reported use of cocaine or depressants in the past year, and therefore data on these drug classes are not provided. Past-Year
Prevalence
of CPU
and SPU
Past-year CPU and SPU prevalence rates were computed across all drug combinations for all subjects, men and women, and for groups defined by their use of a single drug (e.g., alcohol users). An SPU : CPU ratio was computed for each group; the ratio describes the proportion of concurrent users who also are simultaneous users. The data are presented in Table 2. Over 35% of the sample reported SPU during the past year. Chi-square tests Table 2. Percentage of Subjects by Gender and Drug-Use Group Who Reported CPU, SPU, and the SPU:CPU Ratio, Which Describes the Proportion of Concurrent Users Who Also Are Simultaneous Users Subject
Group
All Subjects (n = 575) Men (n = 289) Women (n = 236) Alcohol Users (n = 486) Tobacco Users (?I = 193) Marijuana Users (n = 136) Hallucinogen Users (n = 31)
% CPU
% SPU
SPU:CPU
41.6
35.3
.85
46.0
39.1
.85
39.4
33.1
.84
48.6
39.9
.82
100.0
84.9
.89
100.0
88.9
.89
100.0
93.5
.93
Simultaneous
and Concurrent
Use
323
revealed that gender differences in CPU (46% male vs. 39% female; p > . 10) and SPU (39% male vs. 33% female; p > .lO) did not reach statistical significance. All single-drug users drank alcohol. Subjects who reported use of tobacco, marijuana, and hallucinogens also reported CPU, and a majority (84.9% to 93.5%) also reported SPU. The SPU : CPU ratios reveal that a large proportion of concurrent users also were simultaneous users. This ratio was quite stable across the different groups (range = .82-.93). These data are consistent with other SPU : CPU ratios (Grant & Harford, 1990; Norton & Colliver, 1988). Simultaneous
Polydrug
Use Combinations
The percentage of subjects who reported use of each two-drug combination was computed. Alcohol and tobacco was the most common combination (21.1% of subjects; average frequency among users = 28.0 times/year), followed by alcohol and marijuana (14.7%; average frequency = 25.1 times/year), tobacco and marijuana (7.3%; average frequency = 12.5 times/year), alcohol and hallucinogens (2.1%; average frequency = 10.2 times/year), and marijuana and hallucinogens (1 .S%; average frequency = 8.0 times/year). Discriminant
Function
Analysis:
Single-Drug
Versus Polydrug
Users
A discriminant function analysis was performed to examine predictors of single drug use (n = 246) versus polydrug use (n = 220). The single-drug use group was composed entirely of alcohol users. The variables entered into the discriminant function were scores on the Thrill and Adventure Seeking, and the Disinhibition subscales of the SSS, gender, frequency of alcohol use, and age of first alcohol intoxication. Prior probabilities were set to reflect subgroup sizes. Three variables were significant discriminators: (1) the SSS Disinhibition subscale (A = .86, p < .OOl); (2) the SSS Thrill and Adventure Seeking subscale (A = .79, p < .OOl); and (3) gender (A = .78, p < .OOl). Higher sensation seeking and male gender were predictive of polydrug use. The discriminant function correctly classified 18 1 of 246 (73.6%) single-drug users and 150 of 220 (68.2%) polydrug users, for an overall correct classification rate of 7 1%. Discriminant
Function Analysis: Simultaneous Polydrug Nonsimultaneous Polydrug Users
Users Versus
Of the 220 polydrug users, 36 had not engaged in SPU. All 36 subjects reported the use of alcohol and marijuana, or the use of alcohol and tobacco (but not in combination). Of the remaining 184 subjects, 89 (48.4%) reported the simultaneous use only of alcohol and tobacco. Although the simultaneous use of alcohol and tobacco poses important health risks, this pattern has different consequences than other drug combinations that can produce additive and interactive effects on consciousness and behavior. Therefore, the remaining 95 SPU subjects were compared to the 36 nonsimultaneous polydrug users. The predictor variables were the Thrill and Adventure Seeking and the Disin-
C.S. Martin,
324
P.R. Clifford,
and R.L. Clapper
hibition subscales of the SSS, gender, frequency of alcohol use, and age of first alcohol intoxication. Prior probabilities were set to reflect subgroup sizes. Three variables were significant discriminators: (1) the frequency of alcohol use (A = .78, p < .OOl); (2) the SSS Disinhibition subscale (A = .70, p < .OOl); and (3) the SSS Thrill and Adventure Seeking subscale (A = .68, p < .OOl). High sensation seeking and a greater frequency of alcohol use were predictive of SPU. The discriminant function correctly classified 87 of 95 (91.6%) SPU subjects and 20 of 36 (55.6%) nonsimultaneous polydrug users, for an overall correct classification rate of 81.7%. It is not clear whether the association of alcohol use frequency with SPU was simply due to the fact that alcohol was a part of most two-drug combinations. However, subjects who reported combined use of marijuana and hallucinogens reported a greater alcohol use frequency than nonsimultaneous polydrug users (p < .05).
DISCUSSION In this sample of first-year college students, there were substantial rates of past-year polydrug use for alcohol, tobacco, marijuana, and to a lesser extent, hallucinogens. A majority of concurrent polydrug users also were simultaneous polydrug users: Percentages ranged from 82% to 93%. These data are consistent with previous reports on CPU and SPU (Grant & Harford, 1990; Norton & Colliver, 1988). Because SPU has seldom been assessed, previous research examining only CPU may not entirely reflect the health and safety consequences of polydrug use. Rates of SPU were found to vary by drug combination. The most frequent two-drug combination was alcohol and tobacco, followed by alcohol and marijuana, tobacco and marijuana, and then alcohol and hallucinogens. Due to additive or interactive effects, alcohol-marijuana and alcohol-hallucinogen combinations may pose special health and safety risks beyond those associated with the use of these substances in isolation. Importantly, guidelines concerning safe levels of alcohol consumption, which are provided in some prevention programs, often will not apply to the combined use of alcohol and other drugs. The present data, although cross sectional, are consistent with research on the order of initiation of use of multiple drugs in adolescence. Kandel and Faust (1975) found that, with few exceptions, multiple drug users begin by using alcohol and/or tobacco, then marijuana, and then other drugs such as hallucinogens and cocaine. The current data are consistent with the hypothesis that SPU patterns follow a similar temporal order. Remarkably, all 246 single-drug users were alcohol users, and among all polydrug users, alcohol was one of the drugs used. Alcohol and tobacco was the most common two-drug combination, followed by alcohol and marijuana, and then tobacco and marijuana. These results suggest the need for longitudinal studies of the order of initiation of use of drug combinations, to examine whether temporal patterns of SPU characterize most users who eventually progress to combinations that involve hallucinogens, cocaine, depressants, and opiates (Lex, 1990). The high proportion of subjects who reported combined use of alcohol and tobacco may not appear surprising, given the strong association of alcohol and
Simultaneous
and Concurrent
Use
325
nicotine use and dependence in other studies (e.g., DiFranza & Guerrera, 1990; Kandel & Logan, 1984; Single et al., 1985). However, the combined use of alcohol and tobacco reported here is of particular interest because the sample contained a high proportion of nondaily smokers who presumably were beginning to experiment with tobacco use (see Table 1). The current data provide some support for the idea that the use of alcohol is an important correlate of nondaily smoking, and may be involved in the etiology of nicotine dependence among those experimenting with tobacco use. Discriminant function analyses revealed that male gender and personality characteristics related to high sensation seeking were predictive of polydrug versus single-drug use. These results are consistent with past research (Andrucci et al., 1989; Jaffe 8c Archer, 1987). A high frequency of alcohol use, and high sensation seeking were predictive of SPU among polydrug users. Sensation seeking may be related to SPU because high sensation seekers find the feelings of intoxication produced by drug combinations more pleasant and reinforcing than other persons. Alcohol use frequency may be associated with SPU because both variables reflect dimensions of drug use severity that covary. Alcohol use frequency was associated with the use of drug combinations that did not include alcohol. The present data on predictors of SPU are exploratory, and many individual difference characteristics were not assessed. The current data are limited by their self-report nature and by the use of a college student sample. Some students did not attend meetings at which assessment occurred or attended the meetings but did not complete the questionnaire. Any effects of selection bias on the data are unknown. Also, patterns and predictors of CPU and SPU may be quite different in other populations. Given the prevalence of CPU and SPU in the current sample, polydrug use patterns may be a source of even greater concern in populations that show greater amounts of alcohol and drug use. More research is needed to examine patterns and predictors of CPU and SPU in alcoholics, persons with drug-induced health problems (e.g., liver disease), and persons at high risk for substance abuse. Because drug combinations can affect intoxication, psychomotor impairment (Sutton, 1983), and health in an additive or synergistic manner, SPU is a particularly important aspect of polydrug use. Researchers need to be aware of these issues. Drug combinations and their consequences should be assessed in biological and epidemiological research. Attention also should be paid to SPU in prevention programs. The current data provide some information about the drug combinations and high-risk subgroups that prevention efforts should target, at least in college students. Rather than simply focusing on the prevention of abuse of single drugs in isolation, some prevention efforts may be best geared toward providing information about the potential harm and negative consequences that can result from the combined use of multiple drugs. REFERENCES Abel,
E., & Dintcheff, B. (1986). tant alcohol administration.
Increased Journal
marijuana-induced fetotoxicity by a low dose of Studies on Alcohol, 47, 440-443.
of concomi-
C.S. Martin,
326 American
P.R. Clifford,
and R.L. Clapper
Psychiatric Association (1987). Diagnostic and statistical manual of mental disorders (3rd rev.) Washington DC: Author. Andrucci, C., Archer, R., Pancoast, D.. & Gordon, R. (1989). The relationship of MMPI and sensation seeking scales to adolescent drug use. Journal of Person@ Assessment, 53, 253-266. Bo, O., Jaftner, J., Langard, 0.. Trumpy, J., Bredesen, J., & Lunde. P. (1975). Ethanol and diazepam as causative agents in road traffic accidents. In S. Israelstand & S. Lambert (Eds.), Alcohol, drugs, and frafic sufelv (pp. 62-81). Toronto: Addiction Research Foundation. Cahalan, D., Cisin, I., & Crossley, H. (1969). American drinkingpracfices. New Brunswick, NJ: Rutgers Center for Alcohol Studies. DiFranza, J., & Guerrera, M. (1990). Alcoholism and smoking. Journal of Sfudies on Alcohol, 51, 130135. Forney, M., Forney, P., & Ripley, W. (1989). Predictor variables of adolescent drinking. Advances in Alcohol and Substance Abuse, 8, 97- 117. Grant, B., & Harford, T. (1990). Concurrent and simultaneous use of alcohol with sedatives and tranquilizers: Results of a national survey. Journal of Substance Abuse, 2, I-14. Hearn, W., Rose, S., Wagner, J., Ciarleglio, A., & Mash, D. (1991). Cocaethylene is more potent than cocaine in mediating lethality. Pharmacology, Eiochemirfry, and Behavior, 39, 531-533. Huba. G., & Bender. P. (1980). The role of peer and adult models for drug taking at different stages in adolescence. Journal of Youth and Adolescence, 9, 449-465. Jaffe, L., & Archer, R. (1987). The prediction of drug use among college students from MMPI, MCMI, and sensation seeking scales. Journal of Personality Assessment, 51, 243-253. Jadow, P., Elsworth, J., Bradberry, C.. Winger. G., & Taylor, J. (1991). Cocaethylene: A neuropharmacologically active metabolite associated with concurrent cocaine-ethanol ingestion. Laye Sciences, 48, 1787- 1794. Kandel, D., & Faust, R. (1975). Sequence and stages in patterns of adolescent drug use. Archives of General Psychiatry, 32, 923-932. Kandel, D., & Logan J. (1984). Periods of drug use from adolescence to young adulthood: 1. Periods of risk for initiation, continued use, and discontinuation. American Journal of Public Health, 74, 660-666. Laisi, U., Linnoila, M., Seppala, T., Himberg, J.. & Mattila. M. (1979). Pharmacodynamic interactions of diazepam with different alcoholic beverages. European Journal of Clinical Pharmucology, 16, 263-270. Lex, B. (1990). Male heroin addicts and their female mates: Impact on disorder and recovery. Journal of Substance Abuse, 2, 147- 177. Martin, C., Clapper, R., & Clifford, P. (1991, J une) Quaniitylfrequency use patterns for alcohol and other drugs. Poster presented at a meeting of the Research Society on Alcoholism, Marco Island, FL. Newcomb, M., Maddahian, E., & Bender, P. (1986). Risk factors for drug use among adolescents: Concurrent and longitudinal analyses. American Journal of Public Health, 76, 525-53 1. Norton, R., & Colliver. J. (1988). Prevalence and patterns of combined alcohol and marijuana use. Journal of Studies on Alcohol, 49, 378-380. Single, D., Kandel, D., & Faust, R. (1985). Patterns of multiple drug use in high school. Journal of Health and Social Behavior, 32, 344-357. Stein, J., Newcomb, M., & Bender, P. (1987). An 8-year study of multiple influences on drug use and drug use consequences. Joumul of Personality and Social Psychology, 53, 1094-l 105. Sutton, L. (1983). The effects of alcohol, marijuana and their combination on driving ability. Journal of Studies on Alcohol, 44, 438-445. Wilkinson, D., Leigh, G., Cordingley, J., Martin, G., & Lei, H. (1987). Dimensions of multiple drug use and a typology of drug users. British Journal of Addiction, 82, 259-273. Zuckerman, M. (1979). Sensation seeking: Beyond the optimal level of arousal. Hillsdale, NJ: Erlbaum. ed.,
of Substance
Abuse,
4,3 19-326
f 1992)
BRIEF REPORT
Patterns and Predictors of Simultaneous and Concurrent Use of Alcohol, Tobacco, Marijuana, and Hallucinogens in First-Year College Students Christopher S. Martin Western University
Psychiatric Institute and Clinic Department of Psychiatry of Pittsburgh School of Medicine
Patrick R. Clifford Rock 1. Clapper Center for Alcohol
and Addiction Studies Brown University
Polydrug use produces important health and safety risks. Little research has examined whether multiple drugs are used simultaneously (at the same time or in close temporal sequence). Instead, researchers have assessed concurrent polydrug use (the use of multiple drugs within a given time period such as years or months). The research here examined patterns and predictors of both simultaneous and concurrent polydrug use in 575 first-year college students. Both concurrent and simultaneous polydrug use were common for alcohol, tobacco, and marijuana. The percentage of concurrent polydrug users who were also simultaneous polydrug users ranged from 82% to 93% across subgroups defined by gender and the use of a single drug. Male gender, high levels of sensation seeking, and frequent alcohol use predicted single-drug versus polydrug use status as well as simultaneous polydrug use. Patterns and predictors of simultaneous and concurrent polydrug use should be addressed in prevention research and preventative interventions.
Polydrug use is a major health and safety concern, and is common among adolescent and young adult drug users. The comorbidity of alcohol and drug use diagnoses is increasingly recognized (American Psychiatric Association, 1987; DiFranza & Guerrera, 1990; Wilkinson, Leigh, Cordingley, Martin, 8c Lei, 1987). Research has examined predictors of polydrug use (Forney, Forney, & We thank David Lewis, Bruce Donovon, Toby Simon, Mary Grenedier. and Carol Cohen for their assistance in conducting this research. Parts of this report were presented at the annual meeting of the Research Society on Alcoholism, Marco Island, FL, June 8-13, 1991. Correspondence and requests for reprints should be sent to Christopher S. Martin, Western Psychiatric Institute and Clinic, Department of Psychiatry, University of Pittsburgh School of Medicine, 381 I O’Hara Street, Pittsburgh, PA 15213-2593. 319
C.S. Martin,
320
P.R. Clifford,
and R.L. Clapper
Ripley, 1989; Newcomb, Maddahian, & Bentler, 1986), and the order of initiation of use of multiple drugs (Kandel & Faust, 1975; Single, Kandel, 8c Faust, 1985). Use of more than one drug at the same time or in close temporal proximity has been termed simultaneous polydrug u.re (SPU; Grant & Harford, 1990). The use of more than one drug in the same time period (e.g., a year), but not necessarily at the same time, has been termed concurrent pofydrug use (CPU). Thus, SPU is a subset of CPU. Using data from a national sample, Grant and Harford reported CPU and SPU patterns for alcohol with sedatives and tranquilizers. A majority of concurrent users also were simultaneous users. Norton and Colliver (1988) reported data on combined use of marijuana and alcohol from a national sample. Combined use patterns were most common in persons aged 18-34. Most men (79%) and women (67%) who used alcohol and marijuana concurrently also used these drugs simultaneously. Aside from these reports, little is known about SPU patterns. Most research on polydrug use has not assessed whether multiple drugs were used in combination (i.e., simultaneously). Little is known about which drugs are and are not used in combination. Drug combinations can pose special health and safety risks (Abel & Dintcheff, 1986; Bo et al., 1975; Laisi, Linnoila, Seppala, Himberg, & Mattila, 1979; Sutton, 1983). For example, recent research indicates that simultaneous ingestion of alcohol and cocaine produces a novel stimulant compound cocaethylene (Jatlow, Elsworth, Bradberry, Winger, & Taylor, 199 l), which has a greater acute toxicity than does cocaine (Hearn, Rose, Wagner, Ciarleglio, & Mash, 1991). Therefore SPU data are vital for targeting relevant behaviors in prevention efforts. Researchers have not examined variables associated with SPU other than demographic characteristics. Previous research has found that personality characteristics related to disinhibition and sensation seeking are related to CPU (Andrucci, Archer, Pancoast, & Gordon, 1989; Jaffe & Archer, 1987; Zuckerman, 1979). Other research has linked concurrent drug use to age of first use of substances and peer use (Huba & Bentler, 1980; Stein, Newcomb, & Bentler, 1987). The association of personality and age of first use with SPU would suggest determinants of particular drug use patterns, and would identify high-risk subgroups for prevention efforts. The research here examined patterns and predictors of CPU and SPU in first-year college students. The proportion of concurrent and simultaneous users was calculated for the entire sample, and for different subgroups. The relative frequencies of different drug combinations were examined. Discriminant function analyses were used to examine variables that differentiated (1) single-drug users from polydrug users, and (2) polydrug users who did and did not engage in SPU. METHOD Subjects Subjects were 575 first-year students at a private university in New England. The mean age was 17.8 years (SD = 0.56). The sample comprised 42.7% of the
Simultaneous
and Concurrent
Use
321
entire first-year class. Fifty percent of the subjects were male, 4 1% were female, and 9% of the subjects left this item blank. The sample was 66.2% Caucasian, 12.9% Asian, 6.4% African-American, 4.5% Latino, and the remaining 10% of the subjects reported other ethnic identifications or left this item blank. Procedure Participation was voluntary and occurred at the beginning of the fall semester so that reports of past-year drug use would apply to senior year in high school and the following summer. Testing occurred during regularly scheduled student meetings, in groups of 10 to 50 students. Thirty of a total of 33 student groups were assessed. Although exact data were not available, approximately 2/9 of students attended these meetings, and of those, about 80% completed the questionnaire. An experimenter explained the purposes of the study and instructions on completing the questionnaire, and told subjects their responses would be confidential and anonymous. The experimenter remained in the room for the entire testing period and answered any questions. Questionnaire A multiple-choice questionnaire was developed for this project. Subjects reported age and gender and completed the Disinhibition, and the Thrill and Adventure Seeking subscales of the Sensation Seeking Scale (SSS; Zuckerman, 1979). Subjects reported past-year use of alcohol, tobacco, marijuana, hallucinogens, cocaine, and depressants. For each drug class, subjects reported age of first use and first intoxication, and the past-year average quantity and frequency of use. Quantity was defined as the amount used per occasion of use. Simultaneity was assessed by asking subjects about drugs used “at the same time.” Instructions read: “By ‘at the same time,’ we mean using another drug while you are still using or feeling the effects of the first drug.” Frequency questions were modeled after other self-report drug-taking measures (e.g., Cahalan, Cisin, & Crossley, 1969). Q uantity questions were worded as “Over the past year, when you used , how much, on the average, did you use?” A vocabulary was pilot tested for assessing the quantity of use of illicit drugs (Martin, Clapper, 8c Clifford, 199 1). Marijuana was assessed as the number of “hits/puffs,” cocaine as the number of “grams,” hallucinogens as the number of “hits” of LSD or “grams” of mushrooms and peyote. Subjects also reported the specific two-drug combinations that they used simultaneously in the past year. RESULTS Past-Year Use of the Six Drug Classes Polydrug use patterns are examined in the context of the past-year use of the different drug classes. Table 1 gives the percentage of subjects who reported use of four drug classes, and the average quantity and frequency of use among users.
322
C.S. Martin,
P.R. Clifford,
and
R.L. Clapper
Table 1. The Percentage of Subjects Who Reported Use of Alcohol, Tobacco, Marijuana, and Hallucinogens in the Past Year and Quantity and Frequency Among Users Past-Year Drug
Class
Alcohol Tobacco Marijuana Hallucinogens
Use
Average
Quantity’
(%I
M
(SD)
84.5 33.6 23.6 5.4
3.2 4.2 6.5 1.2
(2.10) (3.50) (3.50) (0.78)
Average
Frequencyh M (SD)
.80 I .60 .42 .16
(0.96) (2.50) (0.91) (0.29)
“Quantity was deftned as the amount used per occasion of use, and was measured as the number of “drinks” for alcohol, the number of “cigarettes” per day for tobacco, the number of “hits” or “puffs” for mariljuana, and the number of “hits” or “grams” for hallucinogens. “Frequency is expressed as the average number of days per week a given drug was used over the past year.
There was a substantial amount of past-year use of alcohol, tobacco, marijuana, and to a lesser extent, hallucinogens. Less than 2% of the sample reported use of cocaine or depressants in the past year, and therefore data on these drug classes are not provided. Past-Year
Prevalence
of CPU
and SPU
Past-year CPU and SPU prevalence rates were computed across all drug combinations for all subjects, men and women, and for groups defined by their use of a single drug (e.g., alcohol users). An SPU : CPU ratio was computed for each group; the ratio describes the proportion of concurrent users who also are simultaneous users. The data are presented in Table 2. Over 35% of the sample reported SPU during the past year. Chi-square tests Table 2. Percentage of Subjects by Gender and Drug-Use Group Who Reported CPU, SPU, and the SPU:CPU Ratio, Which Describes the Proportion of Concurrent Users Who Also Are Simultaneous Users Subject
Group
All Subjects (n = 575) Men (n = 289) Women (n = 236) Alcohol Users (n = 486) Tobacco Users (?I = 193) Marijuana Users (n = 136) Hallucinogen Users (n = 31)
% CPU
% SPU
SPU:CPU
41.6
35.3
.85
46.0
39.1
.85
39.4
33.1
.84
48.6
39.9
.82
100.0
84.9
.89
100.0
88.9
.89
100.0
93.5
.93
Simultaneous
and Concurrent
Use
323
revealed that gender differences in CPU (46% male vs. 39% female; p > . 10) and SPU (39% male vs. 33% female; p > .lO) did not reach statistical significance. All single-drug users drank alcohol. Subjects who reported use of tobacco, marijuana, and hallucinogens also reported CPU, and a majority (84.9% to 93.5%) also reported SPU. The SPU : CPU ratios reveal that a large proportion of concurrent users also were simultaneous users. This ratio was quite stable across the different groups (range = .82-.93). These data are consistent with other SPU : CPU ratios (Grant & Harford, 1990; Norton & Colliver, 1988). Simultaneous
Polydrug
Use Combinations
The percentage of subjects who reported use of each two-drug combination was computed. Alcohol and tobacco was the most common combination (21.1% of subjects; average frequency among users = 28.0 times/year), followed by alcohol and marijuana (14.7%; average frequency = 25.1 times/year), tobacco and marijuana (7.3%; average frequency = 12.5 times/year), alcohol and hallucinogens (2.1%; average frequency = 10.2 times/year), and marijuana and hallucinogens (1 .S%; average frequency = 8.0 times/year). Discriminant
Function
Analysis:
Single-Drug
Versus Polydrug
Users
A discriminant function analysis was performed to examine predictors of single drug use (n = 246) versus polydrug use (n = 220). The single-drug use group was composed entirely of alcohol users. The variables entered into the discriminant function were scores on the Thrill and Adventure Seeking, and the Disinhibition subscales of the SSS, gender, frequency of alcohol use, and age of first alcohol intoxication. Prior probabilities were set to reflect subgroup sizes. Three variables were significant discriminators: (1) the SSS Disinhibition subscale (A = .86, p < .OOl); (2) the SSS Thrill and Adventure Seeking subscale (A = .79, p < .OOl); and (3) gender (A = .78, p < .OOl). Higher sensation seeking and male gender were predictive of polydrug use. The discriminant function correctly classified 18 1 of 246 (73.6%) single-drug users and 150 of 220 (68.2%) polydrug users, for an overall correct classification rate of 7 1%. Discriminant
Function Analysis: Simultaneous Polydrug Nonsimultaneous Polydrug Users
Users Versus
Of the 220 polydrug users, 36 had not engaged in SPU. All 36 subjects reported the use of alcohol and marijuana, or the use of alcohol and tobacco (but not in combination). Of the remaining 184 subjects, 89 (48.4%) reported the simultaneous use only of alcohol and tobacco. Although the simultaneous use of alcohol and tobacco poses important health risks, this pattern has different consequences than other drug combinations that can produce additive and interactive effects on consciousness and behavior. Therefore, the remaining 95 SPU subjects were compared to the 36 nonsimultaneous polydrug users. The predictor variables were the Thrill and Adventure Seeking and the Disin-
C.S. Martin,
324
P.R. Clifford,
and R.L. Clapper
hibition subscales of the SSS, gender, frequency of alcohol use, and age of first alcohol intoxication. Prior probabilities were set to reflect subgroup sizes. Three variables were significant discriminators: (1) the frequency of alcohol use (A = .78, p < .OOl); (2) the SSS Disinhibition subscale (A = .70, p < .OOl); and (3) the SSS Thrill and Adventure Seeking subscale (A = .68, p < .OOl). High sensation seeking and a greater frequency of alcohol use were predictive of SPU. The discriminant function correctly classified 87 of 95 (91.6%) SPU subjects and 20 of 36 (55.6%) nonsimultaneous polydrug users, for an overall correct classification rate of 81.7%. It is not clear whether the association of alcohol use frequency with SPU was simply due to the fact that alcohol was a part of most two-drug combinations. However, subjects who reported combined use of marijuana and hallucinogens reported a greater alcohol use frequency than nonsimultaneous polydrug users (p < .05).
DISCUSSION In this sample of first-year college students, there were substantial rates of past-year polydrug use for alcohol, tobacco, marijuana, and to a lesser extent, hallucinogens. A majority of concurrent polydrug users also were simultaneous polydrug users: Percentages ranged from 82% to 93%. These data are consistent with previous reports on CPU and SPU (Grant & Harford, 1990; Norton & Colliver, 1988). Because SPU has seldom been assessed, previous research examining only CPU may not entirely reflect the health and safety consequences of polydrug use. Rates of SPU were found to vary by drug combination. The most frequent two-drug combination was alcohol and tobacco, followed by alcohol and marijuana, tobacco and marijuana, and then alcohol and hallucinogens. Due to additive or interactive effects, alcohol-marijuana and alcohol-hallucinogen combinations may pose special health and safety risks beyond those associated with the use of these substances in isolation. Importantly, guidelines concerning safe levels of alcohol consumption, which are provided in some prevention programs, often will not apply to the combined use of alcohol and other drugs. The present data, although cross sectional, are consistent with research on the order of initiation of use of multiple drugs in adolescence. Kandel and Faust (1975) found that, with few exceptions, multiple drug users begin by using alcohol and/or tobacco, then marijuana, and then other drugs such as hallucinogens and cocaine. The current data are consistent with the hypothesis that SPU patterns follow a similar temporal order. Remarkably, all 246 single-drug users were alcohol users, and among all polydrug users, alcohol was one of the drugs used. Alcohol and tobacco was the most common two-drug combination, followed by alcohol and marijuana, and then tobacco and marijuana. These results suggest the need for longitudinal studies of the order of initiation of use of drug combinations, to examine whether temporal patterns of SPU characterize most users who eventually progress to combinations that involve hallucinogens, cocaine, depressants, and opiates (Lex, 1990). The high proportion of subjects who reported combined use of alcohol and tobacco may not appear surprising, given the strong association of alcohol and
Simultaneous
and Concurrent
Use
325
nicotine use and dependence in other studies (e.g., DiFranza & Guerrera, 1990; Kandel & Logan, 1984; Single et al., 1985). However, the combined use of alcohol and tobacco reported here is of particular interest because the sample contained a high proportion of nondaily smokers who presumably were beginning to experiment with tobacco use (see Table 1). The current data provide some support for the idea that the use of alcohol is an important correlate of nondaily smoking, and may be involved in the etiology of nicotine dependence among those experimenting with tobacco use. Discriminant function analyses revealed that male gender and personality characteristics related to high sensation seeking were predictive of polydrug versus single-drug use. These results are consistent with past research (Andrucci et al., 1989; Jaffe 8c Archer, 1987). A high frequency of alcohol use, and high sensation seeking were predictive of SPU among polydrug users. Sensation seeking may be related to SPU because high sensation seekers find the feelings of intoxication produced by drug combinations more pleasant and reinforcing than other persons. Alcohol use frequency may be associated with SPU because both variables reflect dimensions of drug use severity that covary. Alcohol use frequency was associated with the use of drug combinations that did not include alcohol. The present data on predictors of SPU are exploratory, and many individual difference characteristics were not assessed. The current data are limited by their self-report nature and by the use of a college student sample. Some students did not attend meetings at which assessment occurred or attended the meetings but did not complete the questionnaire. Any effects of selection bias on the data are unknown. Also, patterns and predictors of CPU and SPU may be quite different in other populations. Given the prevalence of CPU and SPU in the current sample, polydrug use patterns may be a source of even greater concern in populations that show greater amounts of alcohol and drug use. More research is needed to examine patterns and predictors of CPU and SPU in alcoholics, persons with drug-induced health problems (e.g., liver disease), and persons at high risk for substance abuse. Because drug combinations can affect intoxication, psychomotor impairment (Sutton, 1983), and health in an additive or synergistic manner, SPU is a particularly important aspect of polydrug use. Researchers need to be aware of these issues. Drug combinations and their consequences should be assessed in biological and epidemiological research. Attention also should be paid to SPU in prevention programs. The current data provide some information about the drug combinations and high-risk subgroups that prevention efforts should target, at least in college students. Rather than simply focusing on the prevention of abuse of single drugs in isolation, some prevention efforts may be best geared toward providing information about the potential harm and negative consequences that can result from the combined use of multiple drugs. REFERENCES Abel,
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