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. 2015 Jul;132(1):60-8.
doi: 10.1111/acps.12382. Epub 2015 Jan 9.

Alcohol confounds relationship between cannabis misuse and psychosis conversion in a high-risk sample

A M Auther  1   2 , K S Cadenhead  3 , R E Carrión  1   2   4 , J Addington  5 , C E Bearden  6 , T D Cannon  7   8 , T H McGlashan  8 , D O Perkins  9 , L Seidman  10 , M Tsuang  3 , E F Walker  11 , S W Woods  8 , B A Cornblatt  1   2   4
Affiliations

Alcohol confounds relationship between cannabis misuse and psychosis conversion in a high-risk sample

A M Auther et al. Acta Psychiatr Scand. 2015 Jul.

Abstract

Objective: Cannabis use has been examined as a predictor of psychosis in clinical high-risk (CHR) samples, but little is known about the impact of other substances on this relationship.

Method: Substance use was assessed in a large sample of CHR participants (N = 370, mean age = 18.3) enrolled in the multisite North American Prodrome Longitudinal Study Phase 1 project. Three hundred and forty-one participants with cannabis use data were divided into groups: No Use (NU, N = 211); Cannabis Use without impairment (CU, N = 63); Cannabis Abuse/Dependence (CA/CD, N = 67). Participants (N = 283) were followed for ≥2 years to determine psychosis conversion.

Results: Alcohol (45.3%) and cannabis (38.1%) were the most common substances. Cannabis use groups did not differ on baseline attenuated positive symptoms. Seventy-nine of 283 participants with cannabis and follow-up data converted to psychosis. Survival analysis revealed significant differences between conversion rates in the CA/CD group compared with the No Use (P = 0.031) and CU group (P = 0.027). CA/CD also significantly predicted psychosis in a regression analysis, but adjusting for alcohol use weakened this relationship.

Conclusion: The cannabis misuse and psychosis association was confounded by alcohol use. Non-impairing cannabis use was not related to psychosis. Results highlight the need to control for other substance use, so as to not overstate the cannabis/psychosis connection.

Keywords: alcohol use; cannabis use; clinical high-risk; prodromal states; psychosis; substance use.

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Conflict of interest statement

Declaration of interest

No other authors report conflict of interests.

Figures

Fig. 1
Fig. 1
Kaplan–Meier survival analysis depicting time to conversion (in months) for high-risk subjects with no cannabis use vs. cannabis use without impairment vs. cannabis abuse/dependence.
See this image and copyright information in PMC

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