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Original Investigation |

Association Between Lifetime Marijuana Use and Cognitive Function in Middle Age The Coronary Artery Risk Development in Young Adults (CARDIA) Study

Reto Auer, MD, MAS1,2; Eric Vittinghoff, PhD, MPH1; Kristine Yaffe, MD1,3; Arnaud Künzi, BA2; Stefan G. Kertesz, MD, MSc4,5; Deborah A. Levine, MD, MPH6,7,8,9; Emiliano Albanese, MD, PhD, MPH10; Rachel A. Whitmer, PhD11; David R. Jacobs Jr, PhD12; Stephen Sidney, MD11; M. Maria Glymour, ScD, MS1; Mark J. Pletcher, MD, MPH1
[+] Author Affiliations
1Department of Epidemiology and Biostatistics, University of California–San Francisco
2Department of Ambulatory Care and Community Medicine, University of Lausanne, Lausanne, Switzerland
3Department of Psychiatry and Neurology, University of California–San Francisco
4Center for Surgical Medical and Acute Care Research, Birmingham Veterans Affairs Medical Center, Birmingham, Alabama
5Department of Medicine, University of Alabama at Birmingham School of Medicine
6Department of Internal Medicine, University of Michigan Medical School, Ann Arbor
7Veterans Affairs Center for Clinical Management Research, Ann Arbor, Michigan
8Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor
9Department of Neurology and Stroke Program, University of Michigan, Ann Arbor
10Department of Psychiatry, University of Geneva, Geneva, Switzerland
11Kaiser Permanente Division of Research, Oakland, California
12Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis
JAMA Intern Med. 2016;176(3):352-361. doi:10.1001/jamainternmed.2015.7841.
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Importance  Marijuana use is increasingly common in the United States. It is unclear whether it has long-term effects on memory and other domains of cognitive function.

Objective  To study the association between cumulative lifetime exposure to marijuana use and cognitive performance in middle age.

Design, Setting, and Participants  We used data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, a cohort of 5115 black and white men and women aged 18 to 30 years at baseline from March 25, 1985, to June 7, 1986 (year 0), and followed up over 25 years from June 7, 1986, to August 31, 2011, to estimate cumulative years of exposure to marijuana (1 year = 365 days of marijuana use) using repeated measures and to assess associations with cognitive function at year 25. Linear regression was used to adjust for demographic factors, cardiovascular risk factors, tobacco smoking, use of alcohol and illicit drugs, physical activity, depression, and results of the mirror star tracing test (a measure of cognitive function) at year 2. Data analysis was conducted from June 7, 1986, to August 31, 2011.

Main Outcomes and Measures  Three domains of cognitive function were assessed at year 25 using the Rey Auditory Verbal Learning Test (verbal memory), the Digit Symbol Substitution Test (processing speed), and the Stroop Interference Test (executive function).

Results  Among 3385 participants with cognitive function measurements at the year 25 visit, 2852 (84.3%) reported past marijuana use, but only 392 (11.6%) continued to use marijuana into middle age. Current use of marijuana was associated with worse verbal memory and processing speed; cumulative lifetime exposure was associated with worse performance in all 3 domains of cognitive function. After excluding current users and adjusting for potential confounders, cumulative lifetime exposure to marijuana remained significantly associated with worse verbal memory. For each 5 years of past exposure, verbal memory was 0.13 standardized units lower (95% CI, −0.24 to −0.02; P = .02), corresponding to a mean of 1 of 2 participants remembering 1 word fewer from a list of 15 words for every 5 years of use. After adjustment, we found no associations with lower executive function (–0.03 [95% CI, −0.12 to 0.07]; P = .56) or processing speed (–0.04 [95% CI, −0.16 to 0.08]; P = .51).

Conclusions and Relevance  Past exposure to marijuana is associated with worse verbal memory but does not appear to affect other domains of cognitive function.

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Associations Between Lifetime Exposure to Marijuana and Cognitive Function

Years of marijuana use modeled flexibly and current marijuana users at the year 25 visit excluded (n = 392). Results are adjusted for age, race/ethnicity, sex, study site, educational level, cigarette smoking, alcohol use, illicit drug use, cardiovascular risk factors, depression, mirror star tracing test score at the year 2 visit, and differential likelihood of follow-up (see the Methods section). All test results are standardized, such that a 1-U negative deviation indicates 1-SD worse cognitive function than the mean. Histograms describe the distribution of marijuana-years in participants in the Coronary Artery Risk Development in Young Adults study with any exposure to marijuana by presenting the frequency of participants in each considered interval. The inverse of the Stroop score is used in the present analyses to allow interpretation of worse cognitive function with negative standardized scores for all 3 cognitive function tests. DSST indicates Digit Symbol Substitution Test; RAVLT, Rey Auditory Verbal Learning Test.

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Chronic Marijuana Use and Respiratory and Dental Disease
Posted on March 8, 2016
Alan Herman, PhD
Freelance public health researcher
Conflict of Interest: None Declared
Respiratory and dental diseases are other cautions in regard to chronic marijuana use. The inhalation of particulates in marijuana smoke, even with the use of a water pipe, makes the marijuana user, like the tobacco user, at risk for these diseases (Moore et al.,2005; Thomson, et al., 2008). The use pattern may be less marijuana cigarettes smoked than tobacco cigarettes, but the effects of using either drug is the same. The marijuana user, unlike the tobacco cigarette user, and sometimes a person uses both drugs, draws the smoke to get the THC 'high' effect and fills and holds the smoke in the mouth, bronchial tubes and lungs increasing the risks of these diseases, in the same way multiple tobacco cigarettes smoked and less smoke retention creates the same risks (Aldington et al.,2007).

Aldington, S., Williams M., Nowitz, M., Weatherall, M., Pritchard, A., McNaughton, A., Robinson, G., Beasley, R. (2007), Effects of cannabis on pulmonary structure, function and symptoms Thorax, 62:12 1058-1063.

Moore, B. A., Augustson, E. M., Moser, R. P., & Budney, A. J. (2005). Respiratory Effects of Marijuana and Tobacco Use in a U.S. Sample. Journal of General Internal Medicine, 20(1), 33–37.

Thomson W, Poulton R, Broadbent JM, et al. (2008) Cannabis Smoking and Periodontal Disease Among Young Adults. JAMA, 299(5):525-531.
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