Associations between adolescent cannabis use and neuropsychological decline: a longitudinal co‐twin control study
Madeline H. Meier, Avshalom Caspi, Andrea Danese, Helen Louise Fisher, Renate Houts, Louise Arseneault, Terrie E. Moffitt
Addiction July 22, 2017 DOI: 10.1111/add.13946 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Longitudinal co-twin control study Peer reviewed |
|---|---|
| Sample size | 1,989 |
| Population | 1989 twins from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative birth cohort of twins born in England and Wales in 1994-1995 |
| Measures | IQ, Spatial Span reversed |
| Topics | Cannabis |
| Citations | 129 |
| Key findings | Adolescents who used cannabis or met criteria for dependence had lower IQ both before cannabis initiation and at age 18 (e.g., 5.61 and 7.34 IQ points lower at ages 12 and 18 for those with dependence), but showed little evidence of greater IQ decline from ages 12 to 18. Executive function differences at age 18 were generally not apparent within twin pairs, with one exception on a working memory test. The authors conclude that short-term adolescent cannabis use does not appear to cause IQ decline or impair executive functions, and that family background factors explain the observed differences. |
Abstract
Aims: This study tested whether adolescents who used cannabis or met criteria for cannabis dependence showed neuropsychological impairment prior to cannabis initiation and neuropsychological decline from before to after cannabis initiation.
Design: A longitudinal co-twin control study.
Setting: AND
Participants: Participants were 1989 twins from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative birth cohort of twins born in England and Wales from 1994 to 1995.
Measurements: Frequency of cannabis use and cannabis dependence were assessed at age 18. Intelligence quotient (IQ) was obtained at ages 5, 12 and 18. Executive functions were assessed at age 18.
Findings: Compared with adolescents who did not use cannabis, adolescents who used cannabis had lower IQ in childhood prior to cannabis initiation and lower IQ at age 18, but there was little evidence that cannabis use was associated with IQ decline from ages 12-18. For example, adolescents with cannabis dependence had age 12 and age 18 IQ scores that were 5.61 (t = -3.11, P = 0.002) and 7.34 IQ points (t = -5.27, P < 0.001) lower than adolescents without cannabis dependence, but adolescents with cannabis dependence did not show greater IQ decline from age 12-18 (t = -1.27, P = 0.20). Moreover, adolescents who used cannabis had poorer executive functions at age 18 than adolescents who did not use cannabis, but these associations were generally not apparent within twin pairs. For example, twins who used cannabis more frequently than their co-twin performed similarly to their co-twin on five of six executive function tests (Ps > 0.10). The one exception was that twins who used cannabis more frequently than their co-twin performed worse on one working memory test (Spatial Span reversed; β = -0.07, P = 0.036).
Conclusions: Short-term cannabis use in adolescence does not appear to cause IQ decline or impair executive functions, even when cannabis use reaches the level of dependence. Family background factors explain why adolescent cannabis users perform worse on IQ and executive function tests.
Comparable studies
Other observational and cohort studies on cannabis, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| High-potency cannabis and the risk of psychosis People with first episode of psychosis and healthy controls from the local population | 2009 | Case-control study | n = 454 |
| Ayahuasca-Assisted Therapy for Addiction: Results from a Preliminary Observational Study in Canada Rural aboriginal population | 2013 | Observational study | |
| Impaired cognitive performance in drug free users of recreational ecstasy (MDMA) Otherwise healthy young people | 2000 | Observational | |
| Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study Individuals from the general population in Germany aged 14-24 at baseline | 2011 | Observational cohort | n = 1,923 |
| Cannabis-induced psychosis and subsequent schizophrenia-spectrum disorders: follow-up study of 535 incident cases Patients treated for cannabis-induced psychotic symptoms in Denmark between 1994 and... | 2005 | Observational cohort | n = 535 |
Citations in the library
Cited by 16
- Exposure to cannabinoids can lead to persistent cognitive and psychiatric disorders European Journal of Pain February 22, 2019
- Use of Marijuana: Effect on Brain Health: A Scientific Statement From the American Heart Association Stroke February 10, 2022
- The CannTeen study: verbal episodic memory, spatial working memory, and response inhibition in adolescent and adult cannabis users and age-matched controls Psychopharmacology April 29, 2022
- Impaired mnemonic pattern separation associated with PTSD symptoms paradoxically improves with regular cannabis use npj Mental Health Research April 24, 2025
- Psychological and neuropsychological effects of adolescent cannabis use: a structured narrative review. Journal of Addictive Diseases September 30, 2026
and 11 more in the library