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Evaluating the relationship between cannabis use and IQ in youth and young adults at clinical high risk of psychosis

L. Buchy, L. Seidman, Kristin Cadenhead, Tyrone D. Cannon, Barbara Cornblatt, Thomas H. McGlashan, D. Perkins, William S. Stone, Ming T. Tsuang, Elaine F. Walker, S. Woods, Carrie E. Bearden, Daniel H. Mathalon, Jean Addington

Psychiatry Research November 25, 2015 DOI: 10.1016/j.psychres.2015.11.033 (opens in new tab)

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Study at a glance

AI-extracted from the abstract
Characteristics Observational cohort Peer reviewed
Sample size 941
Population 678 youth at clinical high risk (CHR) for psychosis and 263 healthy control participants
Measures Wechsler Abbreviated Scale of Intelligence (Vocabulary and Block Design subtests), Alcohol and Drug Use Scale
Topics Cannabis
Key findings No significant IQ differences appeared between cannabis users and non-users, or across use-frequency groups, in either CHR or healthy control participants. Among CHR participants, late-onset cannabis users had significantly higher IQ than early-onset users, and age at first cannabis use correlated positively with IQ in the CHR group only. The authors suggest age at onset of cannabis use may be more important for IQ than current use or use frequency in CHR youth.

Abstract

Among people with psychosis, those with a history of cannabis use show better cognitive performance than those who are cannabis naïve. It is unknown whether this pattern is present in youth at clinical high risk (CHR) of psychosis. We evaluated relationships between IQ and cannabis use while controlling for use of other substances known to impact cognition in 678 CHR and 263 healthy control (HC) participants. IQ was estimated using the Vocabulary and Block Design subtests of the Wechsler Abbreviated Scale of Intelligence. Drug and alcohol use severity and frequency were assessed with the Alcohol and Drug Use Scale, and we inquired participants’ age at first use. CHR were further separated into early and late age at onset of cannabis use sub-groups, and low-, moderate- and high-frequency sub-groups. No significant differences in IQ emerged between CHR or HC cannabis users vs. non-users, or between use frequency groups. CHR late-onset users showed significantly higher IQ than CHR early-onset users. Age at onset of cannabis use was significantly and positively correlated with IQ in CHR only. Results suggest that age at onset of cannabis may be a more important factor for IQ than use current use or use frequency in CHR.

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

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