ADHD history, not adult cannabis use, drove cognitive deficits in young adults
A childhood ADHD diagnosis was associated with executive function deficits in young adults, but current regular cannabis use was not, though early cannabis initiation before age 16 may matter.
Quick Facts
What This Study Found
Researchers compared cognitive performance in young adults (average age 24) across four groups: those with childhood ADHD who used cannabis, those with ADHD who did not, non-ADHD cannabis users, and non-ADHD non-users. After controlling for IQ, socioeconomic status, alcohol use, and smoking, the ADHD groups performed worse than comparison groups on verbal memory, processing speed, decision-making, working memory, and response inhibition.
No significant effects of adult cannabis use emerged on any cognitive measure. There were also no significant interactions between ADHD and cannabis use, meaning cannabis did not worsen cognitive deficits beyond what ADHD alone produced.
However, exploratory analyses suggested that individuals who began regular cannabis use before age 16 may have poorer executive functioning than those who started later.
Key Numbers
The study included 128 young adults (mean age 24.2 years). The ADHD group showed deficits across six cognitive domains compared to comparison participants. 27 individuals began regular cannabis use before age 16, and 32 began at age 16 or later.
How They Did This
This cross-sectional study compared 87 young adults with childhood ADHD diagnoses (42 cannabis users, 45 non-users) to 41 local comparison participants (20 cannabis users, 21 non-users) on a battery of neuropsychological tests. Cannabis use was defined as past-year monthly or more frequent use. Covariates included age, gender, IQ, socioeconomic status, and past-year alcohol and tobacco use.
Why This Research Matters
This study challenges the assumption that cannabis use in adulthood necessarily adds to the cognitive impairments associated with ADHD. The finding that age of cannabis initiation may matter more than current use aligns with broader research on adolescent brain vulnerability.
The Bigger Picture
ADHD and cannabis use frequently co-occur, and a significantly greater proportion of the ADHD group began using cannabis before age 16. Understanding whether cannabis independently worsens ADHD-related cognitive problems is important for clinical guidance, and this study suggests the answer may depend more on when cannabis use begins than whether it continues in adulthood.
What This Study Doesn't Tell Us
The cross-sectional design cannot determine causation. The cannabis-using groups were relatively small, particularly for the exploratory age-of-onset analysis. Only past-year use was measured, not lifetime cumulative exposure. The study could not fully account for all potential confounds.
Questions This Raises
- ?Would longitudinal tracking show different results?
- ?Does the amount of cannabis used matter more than the binary of use vs. non-use?
- ?What mechanisms might explain the apparent vulnerability of the pre-16 brain to cannabis effects?
Trust & Context
- Key Stat:
- ADHD drove cognitive deficits; adult cannabis use added no measurable impairment
- Evidence Grade:
- Well-controlled cross-sectional comparison with appropriate covariates, but limited by small subgroup sizes and inability to establish causation.
- Study Age:
- Published in 2013. The relationship between ADHD and cannabis continues to be studied.
- Original Title:
- Impact of ADHD and cannabis use on executive functioning in young adults.
- Published In:
- Drug and alcohol dependence, 133(2), 607-14 (2013)
- Authors:
- Tamm, Leanne(5), Epstein, Jeffery N(6), Lisdahl, Krista M(13), Molina, Brooke, Tapert, Susan, Hinshaw, Stephen P, Arnold, L Eugene, Velanova, Katerina, Abikoff, Howard, Swanson, James M
- Database ID:
- RTHC-00742
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Does cannabis make ADHD-related cognitive problems worse?
In this study of young adults, regular cannabis use in adulthood did not add measurable cognitive impairment beyond what the ADHD diagnosis itself produced. However, starting cannabis before age 16 may be linked to worse outcomes.
Does the age you start using cannabis matter for cognition?
Exploratory analyses in this study suggested that individuals who began regular cannabis use before age 16 had poorer executive functioning than those who started later, though these findings need replication in larger samples.
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Cite This Study
https://rethinkthc.com/research/RTHC-00742APA
Tamm, Leanne; Epstein, Jeffery N; Lisdahl, Krista M; Molina, Brooke; Tapert, Susan; Hinshaw, Stephen P; Arnold, L Eugene; Velanova, Katerina; Abikoff, Howard; Swanson, James M. (2013). Impact of ADHD and cannabis use on executive functioning in young adults.. Drug and alcohol dependence, 133(2), 607-14. https://doi.org/10.1016/j.drugalcdep.2013.08.001
MLA
Tamm, Leanne, et al. "Impact of ADHD and cannabis use on executive functioning in young adults.." Drug and alcohol dependence, 2013. https://doi.org/10.1016/j.drugalcdep.2013.08.001
RethinkTHC
RethinkTHC Research Database. "Impact of ADHD and cannabis use on executive functioning in ..." RTHC-00742. Retrieved from https://rethinkthc.com/research/tamm-2013-impact-of-adhd-and
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.