Daily Use, Especially of High-Potency Cannabis, Drives the Earlier Onset of Psychosis in Cannabis Users
- Marta Di Forti*,1,
- Hannah Sallis2,
- Fabio Allegri3,
- Antonella Trotta1,
- Laura Ferraro4,
- Simona A. Stilo5,
- Arianna Marconi1,
- Caterina La Cascia4,
- Tiago Reis Marques1,
- Carmine Pariante6,
- Paola Dazzan1,
- Valeria Mondelli6,
- Alessandra Paparelli1,
- Anna Kolliakou1,
- Diana Prata1,
- Fiona Gaugrhan1,
- Anthony S. David1,
- Craig Morgan5,
- Daniel Sthal7,
- Mizanur Khondoker7,
- James H. MacCabe1,8 and
- Robin M. Murray1,8
+ Author Affiliations
- ↵8Joint last authors.
- ↵*To whom correspondence should be addressed; Department of Psychosis Studies, Institute of Psychiatry, Kings College, De Crespigny Park, London SE5 8AF, UK; tel: 0044207-8480145, fax: 0044207-8480100, e-mail: marta.diforti@kcl.ac.uk
Abstract
Cannabis use is associated with an earlier age of onset of psychosis (AOP). However, the reasons for this remain debated. Methods: We applied a Cox proportional hazards model to 410 first-episode psychosis patients to investigate the association between gender, patterns of cannabis use, and AOP. Results: Patients with a history of cannabis use presented with their first episode of psychosis at a younger age (mean years = 28.2, SD = 8.0; median years = 27.1) than those who never used cannabis (mean years = 31.4, SD = 9.9; median years = 30.0; hazard ratio [HR] = 1.42; 95% CI: 1.16–1.74; P < .001). This association remained significant after controlling for gender (HR = 1.39; 95% CI: 1.11–1.68; P < .001). Those who had started cannabis at age 15 or younger had an earlier onset of psychosis (mean years = 27.0, SD = 6.2; median years = 26.9) than those who had started after 15 years (mean years = 29.1, SD = 8.5; median years = 27.8; HR = 1.40; 95% CI: 1.06–1.84; P = .050). Importantly, subjects who had been using high-potency cannabis (skunk-type) every day had the earliest onset (mean years = 25.2, SD = 6.3; median years = 24.6) compared to never users among all the groups tested (HR = 1.99; 95% CI: 1.50- 2.65; P < .0001); these daily users of high-potency cannabis had an onset an average of 6 years earlier than that of non-cannabis users. Conclusions: Daily use, especially of high-potency cannabis, drives the earlier onset of psychosis in cannabis users.
acesse: http://schizophreniabulletin.oxfordjournals.org/content/early/2013/12/14/schbul.sbt181.abstract