• Online Features  This Article  • Full text  • PDF  • eFigures and eTables  • Reply to article  • Send to a friend  • Save in My Folder  • Save to citation manager  • Permissions  Citing Articles  • Citation map  • Citing articles on HighWire  • Citing articles on Web of Science (18)  • Contact me when this article is cited  Related Content  • Readers Reply  • Similar articles in this journal  Topic Collections  • Neurology  • Behavioral Neurology  • Pediatrics  • Adolescent Medicine  • Psychiatry  • Adolescent Psychiatry  • Psychiatry, Other  • Public Health  • Substance Abuse/ Alcoholism  • Alert me on articles by topic  Social Bookmarking   What's this?

John McGrath, MD, PhD, FRANZCP; Joy Welham, MAPs; James Scott, MBBS, FRANZCP; Daniel Varghese, MBBS, FRANZCP; Louisa Degenhardt, PhD; Mohammad Reza Hayatbakhsh, MD, PhD; Rosa Alati, PhD; Gail M. Williams, PhD; William Bor, MBBS, DPM, FRANZCP; Jake M. Najman, PhD

Arch Gen Psychiatry. 2010;67(5):440-447. Published online March 1, 2010 (doi:10.1001/archgenpsychiatry.2010.6).

Context  Prospective cohort studies have identified an association between cannabis use and later psychosis-related outcomes, but concerns remain about unmeasured confounding variables. The use of sibling pair analysis reduces the influence of unmeasured residual confounding.

Objective  To explore the association between cannabis use and psychosis-related outcomes.

Design  A sibling pair analysis nested within a prospective birth cohort.

Setting  Births at a Brisbane, Australia, hospital.

Participants  Three thousand eight hundred one young adults born between 1981 and 1984 as part of the Mater-University Study of Pregnancy.

Main Outcome Measures  Cannabis use and 3 psychosis-related outcomes (nonaffective psychosis, hallucinations, and Peters et al Delusions Inventory score) were assessed at the 21-year follow-up. Associations between duration since first cannabis use and psychosis-related outcomes were examined using logistic regression adjusted for sex, age, parental mental illness, and hallucinations at the 14-year follow-up. Within 228 sibling pairs, the association between within-pair differences in duration since first cannabis use and Peters et al Delusions Inventory score was examined with general linear modeling. The potential impact of attrition was examined.

Results  Duration since first cannabis use was associated with all 3 psychosis-related outcomes. For those with duration since first cannabis use of 6 or more years, there was a significantly increased risk of (1) nonaffective psychosis (adjusted odds ratio, 2.2; 95% confidence interval, 1.1-4.5), (2) being in the highest quartile of Peters et al Delusions Inventory score (adjusted odds ratio, 4.2; 95% confidence interval, 4.2-5.8), and (3) hallucinations (adjusted odds ratio, 2.8; 95% confidence interval, 1.9-4.1). Within sibling pairs, duration since first cannabis use and higher scores on the Peters et al Delusions Inventory remained significantly associated.

Conclusions  Early cannabis use is associated with psychosis-related outcomes in young adults. The use of sibling pairs reduces the likelihood that unmeasured confounding explains these findings. This study provides further support for the hypothesis that early cannabis use is a risk-modifying factor for psychosis-related outcomes in young adults.

Author Affiliations: Queensland Brain Institute (Dr McGrath) and Department of Psychiatry (Drs McGrath and Scott), University of Queensland, St Lucia, Queensland Centre for Mental Health Research, The Park Centre for Mental Health, Wacol (Dr McGrath and Ms Welham), Child and Youth Mental Health Service, Royal Children's Hospital (Dr Scott), School of Population Health (Drs Hayatbakhsh, Alati, Williams, and Najman), and Centre for Youth Substance Abuse Research (Dr Alati), University of Queensland, Herston, and Department of Psychiatry, Princess Alexandra Hospital, Woolloongabba (Dr Varghese), Queensland, National Drug and Alcohol Research Centre, University of New South Wales, Sydney (Dr Degenhardt), and Mater Children's Hospital, South Brisbane (Dr Bor), Australia.

CiteULike    Connotea    Delicious    Digg    Facebook    Reddit    Technorati    Twitter     What's this?

THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES

Adolescent exposure to cannabis as a risk factor for psychiatric disorders
Rubino et al.
J Psychopharmacol 2012;26:177-188.
ABSTRACT | FULL TEXT  

The need for close monitoring of early psychosis and co-occurring substance misuse
Caton
The Psychiatrist 2011;35:241-243.
ABSTRACT | FULL TEXT  

The Prevention of Schizophrenia
Brown and McGrath
Schizophr Bull 2011;37:257-261.
FULL TEXT  

The "New" Marijuana
Wells and Ott
The Annals of Pharmacotherapy 2011;45:414-417.
ABSTRACT | FULL TEXT  

Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study
Kuepper et al.
BMJ 2011;342:d738-d738.
ABSTRACT | FULL TEXT  

Evidence That Familial Liability for Psychosis Is Expressed as Differential Sensitivity to Cannabis: An Analysis of Patient-Sibling and Sibling-Control Pairs
Genetic Risk and Outcome in Psychosis (GROUP) Inve
Arch Gen Psychiatry 2011;68:138-147.
ABSTRACT | FULL TEXT  

RAPID RESPONSES TO THIS ARTICLE

Does acute cannabis intoxication explain the psychosis link?
Dan Werb
Arch Gen Psychiatry Online, 6 May 2010.
TEXT 

Early Clinical Research on Toxic Effects of Chronic Marihuana (Marijuana) Use
Partam Manalai
Arch Gen Psychiatry Online, 15 Jun 2010.
TEXT 

Cannabis and Psychosis: A bi-directional relationship?
Thomas H Richardson
Arch Gen Psychiatry Online, 15 Jun 2010.
TEXT