Daily Use, Especially of High-Potency Cannabis, Drives the Earlier Onset of Psychosis in Cannabis Users

1. Marta Di Forti*,¹,
2. Hannah Sallis²,
3. Fabio Allegri³,
4. Antonella Trotta¹,
5. Laura Ferraro⁴,
6. Simona A. Stilo⁵,
7. Arianna Marconi¹,
8. Caterina La Cascia⁴,
9. Tiago Reis Marques¹,
10. Carmine Pariante⁶,
11. Paola Dazzan¹,
12. Valeria Mondelli⁶,
13. Alessandra Paparelli¹,
14. Anna Kolliakou¹,
15. Diana Prata¹,
16. Fiona Gaugrhan¹,
17. Anthony S. David¹,
18. Craig Morgan⁵,
19. Daniel Sthal⁷,
20. Mizanur Khondoker⁷,
21. James H. MacCabe¹,⁸ and
22. Robin M. Murray¹,⁸

+ Author Affiliations

1. ¹ Department of Psychosis Studies, Institute of Psychiatry, Kings College London, London, UK;
2. ² School of Social and Community Medicine, Bristol University, Bristol, UK;
3. ³ Department of Psychiatry, Bologna University, Bologna, Italy;
4. ⁴ Department of Psychiatry and Neuroscience, Palermo University, Palermo, Italy;
5. ⁵ Department of Health Services and Public Health, Institute of Psychiatry, Kings College London, London, UK;
6. ⁶ Department of Psychological Medicine, Institute of Psychiatry, Kings College London, London, UK;
7. ⁷ Department of Biostatistics, Institute of Psychiatry, Kings College London, London, UK

1. ↵⁸Joint last authors.
2. ↵*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