This article was downloaded by: [Bangor University] On: 22 December 2014, At: 15:46 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Addictive Diseases Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wjad20
Marijuana and Workplace Safety: An Examination of Urine Drug Tests James W. Price DO, MPH
a
a
St. Mary's Occupational Medicine Clinic , Evansville , Indiana , USA Accepted author version posted online: 27 Jan 2014.Published online: 17 Apr 2014.
Click for updates To cite this article: James W. Price DO, MPH (2014) Marijuana and Workplace Safety: An Examination of Urine Drug Tests, Journal of Addictive Diseases, 33:1, 24-27, DOI: 10.1080/10550887.2014.882729 To link to this article: http://dx.doi.org/10.1080/10550887.2014.882729
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Addictive Diseases, 33:24–27, 2014 C Taylor & Francis Group, LLC Copyright ISSN: 1055-0887 print / 1545-0848 online DOI: 10.1080/10550887.2014.882729
MARIJUANA AND WORKPLACE SAFETY: AN EXAMINATION OF URINE DRUG TESTS James W. Price, DO, MPH
Downloaded by [Bangor University] at 15:46 22 December 2014
St. Mary’s Occupational Medicine Clinic, Evansville, Indiana, USA Although the decriminalization of recreational marijuana and medical marijuana laws provide a compassionate answer for treatment-related issues in patients’ lives, they leave questions open as to the impact on other realms of life, such as employment and safety. This is a case-control study comparing the proportion of marijuana positive urine specimens for postaccident verses random samples. The marijuana concentration of each sample underwent creatinine normalization to account for in vivo dilution. Any sample that tested positive for one or more substances other than marijuana was eliminated from the study. The prevalence of marijuana violations, the odds ratio and 95% confidence interval of accident involvement and the population attributable risk were calculated. A two-by-two table was created with the remaining data and the data were used to calculate the odds ratio, resulting in a value of 0.814 with a 95% confidence interval between 0.625 and 1.060. The Fisher exact probability test generated a 2-tailed P of .139. The subsequent population attributable risk was found to be –1.83%. These findings fail to reject the null hypothesis, and this study failed to demonstrate a statistically significant difference between the numbers of laboratory positive marijuana urine drug tests for a group of random drug tests compared with a group of post-accident drug tests. KEYWORDS. Marijuana, creatinine normalization, urine drug testing, safety
including planning, organizing problem solving, decision making, memory, and control of emotions and behavior.5 Cognitive deficits appear to be accentuated if cannabis use begins before age 15 years.6 Heavy users of cannabis experience more pronounced residual effects of the drug than casual users.7 A study examining 28-day abstinent heavy marijuana abusers found that as the history of the number of joints smoked per week increased, their subsequent performance on tests of memory, executive function, psychomotor speed, and manual dexterity decreased.8 Although decriminalization of recreational marijuana and medical marijuana laws provide a compassionate answer for treatment-related issues in patients’ lives, they leave questions open as to the impact on other realms of life, such as employment and safety.4 The
INTRODUCTION Marijuana is the most commonly used illicit drug. There were 17.4 million past-month users in the United States in 2010.1 Laws have been passed in 17 U.S. states and the District of Columbia that now legalize medical marijuana and are in direct conflict with federal drug-free workplace laws.2 Complicating matters, voters in Colorado and Washington recently approved initiatives to legalize recreational marijuana under state law.3 Although states are progressing in the direction of legalizing marijuana, federal law is clear that marijuana is still an illegal Schedule I controlled drug with no recognized medicinal value.4 Cannabis use appears to impair cognitive functioning on several levels, from motor coordination to executive function tasks
Address correspondence to James W. Price, DO, MPH, St. Mary’s Occupational Medicine Clinic, 2330 Lynch Road, Evansville, IN 47711. E-mail: [email protected]
24
MARIJUANA AND WORKPLACE SAFETY
purpose of this study is to determine if there is a statistical association between marijuana use and work related accidents.
25 TABLE 1. U.S. Department of Transportation Cutoff Criteria (Federal Register, 2008)
Drug
Downloaded by [Bangor University] at 15:46 22 December 2014
MATERIALS AND METHODS This is a case-control study comparing the proportion of marijuana positive urine specimens for post-accident verses random samples. The population consists of employees from a variety of industries mostly located in Southern Indiana, but some are located in Missouri, Kentucky, Ohio and Pennsylvania. There is no distinction made regarding gender, age, or the safety sensitivity of their duties. The study group is comprised of all individuals who presented for a 5-panel post-accident urine drug testing from January 2, 2009, to December 30, 2010. The control group is comprised of all individuals who presented for a 5-panel (amphetamines, cocaine, marijuana, opiates, and phencyclidine) random urine drug testing during the same period. The urine specimens were collected from various sites by trained personnel following standardized collection procedures established by the U.S. Department of Transportation. Each specimen was tested at Clinical Reference Laboratory of Lenexa, Kansas, a U.S. Department of Health and Human Services certified laboratory. A 2-step process was used to assess the samples, beginning with screening the samples using the Siemens ADVIA 2400 immunoassay. Positive screens were confirmed by gas chromatography-mass spectroscopy using an Agilent Instruments 5975 to eliminate false positive specimens. The laboratory also performs validity testing to assess each specimen for substitution and adulteration. Each test was forwarded to a certified medical review officer for interpretation of drug and validity test results, as well as to review of the integrity of the collection and testing process. The data were acquired from an administrative database maintained by Clinical Reference Laboratory as an Excel spreadsheet. The data were converted to a usable file format and processed using Epi Info version 3.5.4. The marijuana concentration of each sample
Amphetamines Cocaine metabolites Marijuana metabolites Opiate metabolites Phencyclidine
Screening cutoff, ng/mL
Confirmation cutoff, ng/mL
500 150 50 2000 25
250 100 15 2000 25
underwent creatinine normalization to account for in vivo dilution. Normalization of drug excretion to urinary creatinine concentration was performed for each drug tested as described by Cone et al.9: ConcentrationCRnormalized = ConcentrationspecimenX (CRreference /CRspecimen ) The reference creatinine was established by referring to the Third National Health and Nutrition Examination Survey (NHANES III) database and using the mean urinary creatinine concentration for the U.S. population (CR reference = 130.4mg/dl) as the reference value.10 Samples that had a marijuana concentration greater than 15 ng/mL were deemed positive.11 The same process was performed for the other drugs tested. Any sample that tested positive for one or more substances other than marijuana was eliminated from the study to correct for the confounding effect of other potentially impairing substances (Table 1). The prevalence of marijuana violations, the odds ratio and 95% confidence interval of accident involvement, and the population attributable risk were calculated. Fisher exact probability test was also performed. The Institutional Review Board of St. Mary’s Medical Center (Evansville, Indiana) approved the study design and granted an inform consent waiver. RESULTS Initially there were 496 samples that tested positive for marijuana. Of these, 145 samples also tested positive for one or more other drugs.
26
J. W. PRICE
TABLE 2. Two-by-Two Table
Downloaded by [Bangor University] at 15:46 22 December 2014
Urine drug test Marijuana
Post-accident
Positive Negative Total
77 884 961
Random 274 2560 2834
Total 351 3444 3795
There were 3963 samples that tested negative for marijuana and 519 of these tested positive for one or more other drugs. Each of the samples that tested positive for drugs other than marijuana was eliminated from the study to control for the effects of the other potentially impairing agents. A two-by-two table was created with the remaining data (Table 2). The data from Table 2 were used to calculate the odd ratio, resulting in a value of 0.814 with the 95% confidence interval being between 0.625 and 1.060. The Fisher exact probability test generated a 2-tailed P value of .139. The subsequent population attributable risk was found to be –1.83%. These findings fail to reject the null hypothesis.
a significantly increased risk of being involved in motor vehicle crashes.12 This study does not delineate between acute marijuana exposure and remote exposure nor does it account for chronicity of drug use and possible tolerance. An evidence-based review reported that light users of cannabis will demonstrate impaired attention and concentration 0 to 6 hours after use, whereas heavy users have no impairment. Both groups will have impaired inhibition and impulsivity, as well as impaired working memory for up to 6 hours after use of the drug. They may or may not have impaired decision making and risk taking during this time.5 The residual effects of cannabis 7 to 20 hours after use are impaired decision making and possible impaired attention/concentration, inhibition/impulsivity, and verbal fluency. The long-term effects after more than 3 weeks of abstinence are essentially the same, with the exception of attention/concentration returning to normal.5 One should also note that urine drug tests should not be used to determine doseconcentration relationships. CONCLUSIONS
DISCUSSION This study fell short of finding an association between marijuana use and involvement of workplace accidents. The study does provide useful information regarding marijuana use in an actual working population. A limitation of this study is that it did not account for the differences of the safety sensitivity of the positions held by each of the urine donors. A 2012 meta-analysis looked at marijuana use as a risk factor for motor vehicle collisions.12 Motor vehicle driving can serve as a safety sensitive employment analog. Analysis of individual studies indicated that the heightened risk of crash involvement associated with marijuana use persisted after adjustment for confounding variables and that the risk of crash involvement increased in a dose-response fashion and the frequency of self-reported marijuana use. The results of this meta-analysis suggest that marijuana use by drivers is associated with
This study failed to demonstrate a statistically significant difference between the numbers of laboratory positive marijuana urine drug tests for a group of random drug tests compared with a group of post-accident drug tests. This study cannot be taken as definitive evidence of absence of an association between marijuana and work-related accidents, but the findings are compelling. Investigations that account for acute impairment, chronicity of use, and safety sensitive responsibilities are warranted. These findings may help direct policymakers and employers to consider the safety sensitivity of an employee’s duties when considering marijuana use in States that are moving toward the legalization of marijuana use. ACKNOWLEDGMENT Dr. Price is the medical review officer for the industries involved in this study.
MARIJUANA AND WORKPLACE SAFETY
Downloaded by [Bangor University] at 15:46 22 December 2014
REFERENCES 1. Substance Abuse and Mental Health Services Administration. Results from the 2010 Nation Survey on Drug Use and Health: Summary of National Findings; NSDUH Series H-41, HHS Publication No. (SMA) 11-4658. Rockville, MD: Substance Abuse and Mental Health Services Administration, 2011. 2. Truxillo DM, Cadiz DM, Bauer TN, Erdogan B. Reactions to employer policies regarding prescription drugs and medical marijuana: the role of safety sensitivity. Journal of Business and Psychology 2013; 28:145–58. 3. Lynch T. The law and politics of marijuana legalization. Policy Forum 2012. 4. Tucker LM. High stakes: how to define “disability” in medical marijuana states in light of the Americans with Disabilities Act, Canadian law, and the impact on employers. Indiana International & Comparative Law Review 2011; 21:359–509. 5. Crean RD, Crane NA, Mason BJ. An evidence based review of acute and longterm effects of cannabis use on executive cognitive functions. J Addict Med 2011; 5: 1–8.
27
6. Fontes MA, Bolla KI, Cunha PJ, et al. Cannabis use before age 15 and subsequent executive functioning. Br J Psychiatry 2011; 198:442–47. 7. Pope HG Jr, Yurgelun-Todd D. The residual cognitive effects of heavy marijuana use in college students. JAMA 1996; 275: 521–7. 8. Bolla KI, Brown K, Eldreth D, Tate K, Cadet JL. Dose-related neurocognitive effects of marijuana use. Neurology 2002; 59:1337– 43. 9. Cone EJ, Caplan YH, Moser F, Robert T, Shelby MK, Black DL. Normalization of urinary drug concentrations with specific gravity and creatinine. J Anal Toxicol 2009; 33:1–7. 10. Barr DB, Wilder LC, Caudill SP, Gonzalez AJ, Needham LL, Pirkle JL. Urinary creatinine concentrations in the U.S. population: implications for urinary biologic monitoring measurements. Environ Health Perspect 2005; 113:192–200. 11. Federal Register. 73 FR 71858; Section 3.4: November 25, 2008 12. Li MC, Brady JE, DiMaggio CJ, Lusardi AR, Tzong KY, Li G. Marijuana use and motor vehicle crashes. Epidemiol Rev 2012; 34:65–72.
Journal of Addictive Diseases Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wjad20
Marijuana and Workplace Safety: An Examination of Urine Drug Tests James W. Price DO, MPH
a
a
St. Mary's Occupational Medicine Clinic , Evansville , Indiana , USA Accepted author version posted online: 27 Jan 2014.Published online: 17 Apr 2014.
Click for updates To cite this article: James W. Price DO, MPH (2014) Marijuana and Workplace Safety: An Examination of Urine Drug Tests, Journal of Addictive Diseases, 33:1, 24-27, DOI: 10.1080/10550887.2014.882729 To link to this article: http://dx.doi.org/10.1080/10550887.2014.882729
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Addictive Diseases, 33:24–27, 2014 C Taylor & Francis Group, LLC Copyright ISSN: 1055-0887 print / 1545-0848 online DOI: 10.1080/10550887.2014.882729
MARIJUANA AND WORKPLACE SAFETY: AN EXAMINATION OF URINE DRUG TESTS James W. Price, DO, MPH
Downloaded by [Bangor University] at 15:46 22 December 2014
St. Mary’s Occupational Medicine Clinic, Evansville, Indiana, USA Although the decriminalization of recreational marijuana and medical marijuana laws provide a compassionate answer for treatment-related issues in patients’ lives, they leave questions open as to the impact on other realms of life, such as employment and safety. This is a case-control study comparing the proportion of marijuana positive urine specimens for postaccident verses random samples. The marijuana concentration of each sample underwent creatinine normalization to account for in vivo dilution. Any sample that tested positive for one or more substances other than marijuana was eliminated from the study. The prevalence of marijuana violations, the odds ratio and 95% confidence interval of accident involvement and the population attributable risk were calculated. A two-by-two table was created with the remaining data and the data were used to calculate the odds ratio, resulting in a value of 0.814 with a 95% confidence interval between 0.625 and 1.060. The Fisher exact probability test generated a 2-tailed P of .139. The subsequent population attributable risk was found to be –1.83%. These findings fail to reject the null hypothesis, and this study failed to demonstrate a statistically significant difference between the numbers of laboratory positive marijuana urine drug tests for a group of random drug tests compared with a group of post-accident drug tests. KEYWORDS. Marijuana, creatinine normalization, urine drug testing, safety
including planning, organizing problem solving, decision making, memory, and control of emotions and behavior.5 Cognitive deficits appear to be accentuated if cannabis use begins before age 15 years.6 Heavy users of cannabis experience more pronounced residual effects of the drug than casual users.7 A study examining 28-day abstinent heavy marijuana abusers found that as the history of the number of joints smoked per week increased, their subsequent performance on tests of memory, executive function, psychomotor speed, and manual dexterity decreased.8 Although decriminalization of recreational marijuana and medical marijuana laws provide a compassionate answer for treatment-related issues in patients’ lives, they leave questions open as to the impact on other realms of life, such as employment and safety.4 The
INTRODUCTION Marijuana is the most commonly used illicit drug. There were 17.4 million past-month users in the United States in 2010.1 Laws have been passed in 17 U.S. states and the District of Columbia that now legalize medical marijuana and are in direct conflict with federal drug-free workplace laws.2 Complicating matters, voters in Colorado and Washington recently approved initiatives to legalize recreational marijuana under state law.3 Although states are progressing in the direction of legalizing marijuana, federal law is clear that marijuana is still an illegal Schedule I controlled drug with no recognized medicinal value.4 Cannabis use appears to impair cognitive functioning on several levels, from motor coordination to executive function tasks
Address correspondence to James W. Price, DO, MPH, St. Mary’s Occupational Medicine Clinic, 2330 Lynch Road, Evansville, IN 47711. E-mail: [email protected]
24
MARIJUANA AND WORKPLACE SAFETY
purpose of this study is to determine if there is a statistical association between marijuana use and work related accidents.
25 TABLE 1. U.S. Department of Transportation Cutoff Criteria (Federal Register, 2008)
Drug
Downloaded by [Bangor University] at 15:46 22 December 2014
MATERIALS AND METHODS This is a case-control study comparing the proportion of marijuana positive urine specimens for post-accident verses random samples. The population consists of employees from a variety of industries mostly located in Southern Indiana, but some are located in Missouri, Kentucky, Ohio and Pennsylvania. There is no distinction made regarding gender, age, or the safety sensitivity of their duties. The study group is comprised of all individuals who presented for a 5-panel post-accident urine drug testing from January 2, 2009, to December 30, 2010. The control group is comprised of all individuals who presented for a 5-panel (amphetamines, cocaine, marijuana, opiates, and phencyclidine) random urine drug testing during the same period. The urine specimens were collected from various sites by trained personnel following standardized collection procedures established by the U.S. Department of Transportation. Each specimen was tested at Clinical Reference Laboratory of Lenexa, Kansas, a U.S. Department of Health and Human Services certified laboratory. A 2-step process was used to assess the samples, beginning with screening the samples using the Siemens ADVIA 2400 immunoassay. Positive screens were confirmed by gas chromatography-mass spectroscopy using an Agilent Instruments 5975 to eliminate false positive specimens. The laboratory also performs validity testing to assess each specimen for substitution and adulteration. Each test was forwarded to a certified medical review officer for interpretation of drug and validity test results, as well as to review of the integrity of the collection and testing process. The data were acquired from an administrative database maintained by Clinical Reference Laboratory as an Excel spreadsheet. The data were converted to a usable file format and processed using Epi Info version 3.5.4. The marijuana concentration of each sample
Amphetamines Cocaine metabolites Marijuana metabolites Opiate metabolites Phencyclidine
Screening cutoff, ng/mL
Confirmation cutoff, ng/mL
500 150 50 2000 25
250 100 15 2000 25
underwent creatinine normalization to account for in vivo dilution. Normalization of drug excretion to urinary creatinine concentration was performed for each drug tested as described by Cone et al.9: ConcentrationCRnormalized = ConcentrationspecimenX (CRreference /CRspecimen ) The reference creatinine was established by referring to the Third National Health and Nutrition Examination Survey (NHANES III) database and using the mean urinary creatinine concentration for the U.S. population (CR reference = 130.4mg/dl) as the reference value.10 Samples that had a marijuana concentration greater than 15 ng/mL were deemed positive.11 The same process was performed for the other drugs tested. Any sample that tested positive for one or more substances other than marijuana was eliminated from the study to correct for the confounding effect of other potentially impairing substances (Table 1). The prevalence of marijuana violations, the odds ratio and 95% confidence interval of accident involvement, and the population attributable risk were calculated. Fisher exact probability test was also performed. The Institutional Review Board of St. Mary’s Medical Center (Evansville, Indiana) approved the study design and granted an inform consent waiver. RESULTS Initially there were 496 samples that tested positive for marijuana. Of these, 145 samples also tested positive for one or more other drugs.
26
J. W. PRICE
TABLE 2. Two-by-Two Table
Downloaded by [Bangor University] at 15:46 22 December 2014
Urine drug test Marijuana
Post-accident
Positive Negative Total
77 884 961
Random 274 2560 2834
Total 351 3444 3795
There were 3963 samples that tested negative for marijuana and 519 of these tested positive for one or more other drugs. Each of the samples that tested positive for drugs other than marijuana was eliminated from the study to control for the effects of the other potentially impairing agents. A two-by-two table was created with the remaining data (Table 2). The data from Table 2 were used to calculate the odd ratio, resulting in a value of 0.814 with the 95% confidence interval being between 0.625 and 1.060. The Fisher exact probability test generated a 2-tailed P value of .139. The subsequent population attributable risk was found to be –1.83%. These findings fail to reject the null hypothesis.
a significantly increased risk of being involved in motor vehicle crashes.12 This study does not delineate between acute marijuana exposure and remote exposure nor does it account for chronicity of drug use and possible tolerance. An evidence-based review reported that light users of cannabis will demonstrate impaired attention and concentration 0 to 6 hours after use, whereas heavy users have no impairment. Both groups will have impaired inhibition and impulsivity, as well as impaired working memory for up to 6 hours after use of the drug. They may or may not have impaired decision making and risk taking during this time.5 The residual effects of cannabis 7 to 20 hours after use are impaired decision making and possible impaired attention/concentration, inhibition/impulsivity, and verbal fluency. The long-term effects after more than 3 weeks of abstinence are essentially the same, with the exception of attention/concentration returning to normal.5 One should also note that urine drug tests should not be used to determine doseconcentration relationships. CONCLUSIONS
DISCUSSION This study fell short of finding an association between marijuana use and involvement of workplace accidents. The study does provide useful information regarding marijuana use in an actual working population. A limitation of this study is that it did not account for the differences of the safety sensitivity of the positions held by each of the urine donors. A 2012 meta-analysis looked at marijuana use as a risk factor for motor vehicle collisions.12 Motor vehicle driving can serve as a safety sensitive employment analog. Analysis of individual studies indicated that the heightened risk of crash involvement associated with marijuana use persisted after adjustment for confounding variables and that the risk of crash involvement increased in a dose-response fashion and the frequency of self-reported marijuana use. The results of this meta-analysis suggest that marijuana use by drivers is associated with
This study failed to demonstrate a statistically significant difference between the numbers of laboratory positive marijuana urine drug tests for a group of random drug tests compared with a group of post-accident drug tests. This study cannot be taken as definitive evidence of absence of an association between marijuana and work-related accidents, but the findings are compelling. Investigations that account for acute impairment, chronicity of use, and safety sensitive responsibilities are warranted. These findings may help direct policymakers and employers to consider the safety sensitivity of an employee’s duties when considering marijuana use in States that are moving toward the legalization of marijuana use. ACKNOWLEDGMENT Dr. Price is the medical review officer for the industries involved in this study.
MARIJUANA AND WORKPLACE SAFETY
Downloaded by [Bangor University] at 15:46 22 December 2014
REFERENCES 1. Substance Abuse and Mental Health Services Administration. Results from the 2010 Nation Survey on Drug Use and Health: Summary of National Findings; NSDUH Series H-41, HHS Publication No. (SMA) 11-4658. Rockville, MD: Substance Abuse and Mental Health Services Administration, 2011. 2. Truxillo DM, Cadiz DM, Bauer TN, Erdogan B. Reactions to employer policies regarding prescription drugs and medical marijuana: the role of safety sensitivity. Journal of Business and Psychology 2013; 28:145–58. 3. Lynch T. The law and politics of marijuana legalization. Policy Forum 2012. 4. Tucker LM. High stakes: how to define “disability” in medical marijuana states in light of the Americans with Disabilities Act, Canadian law, and the impact on employers. Indiana International & Comparative Law Review 2011; 21:359–509. 5. Crean RD, Crane NA, Mason BJ. An evidence based review of acute and longterm effects of cannabis use on executive cognitive functions. J Addict Med 2011; 5: 1–8.
27
6. Fontes MA, Bolla KI, Cunha PJ, et al. Cannabis use before age 15 and subsequent executive functioning. Br J Psychiatry 2011; 198:442–47. 7. Pope HG Jr, Yurgelun-Todd D. The residual cognitive effects of heavy marijuana use in college students. JAMA 1996; 275: 521–7. 8. Bolla KI, Brown K, Eldreth D, Tate K, Cadet JL. Dose-related neurocognitive effects of marijuana use. Neurology 2002; 59:1337– 43. 9. Cone EJ, Caplan YH, Moser F, Robert T, Shelby MK, Black DL. Normalization of urinary drug concentrations with specific gravity and creatinine. J Anal Toxicol 2009; 33:1–7. 10. Barr DB, Wilder LC, Caudill SP, Gonzalez AJ, Needham LL, Pirkle JL. Urinary creatinine concentrations in the U.S. population: implications for urinary biologic monitoring measurements. Environ Health Perspect 2005; 113:192–200. 11. Federal Register. 73 FR 71858; Section 3.4: November 25, 2008 12. Li MC, Brady JE, DiMaggio CJ, Lusardi AR, Tzong KY, Li G. Marijuana use and motor vehicle crashes. Epidemiol Rev 2012; 34:65–72.
