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Original Investigation
March 2016

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

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

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.