Cannabis use, potency linked to psychotic disorder risk.
"We provide the first direct evidence that cannabis use has an effect on variation in the incidence of psychotic disorders," Marta Di Forti, PhD, and her coauthors wrote in the Lancet.
Dr. Di Forti and her coauthors looked at cannabis use in 901 patients presenting with a first psychotic episode to 1 of 11 sites across Europe and Brazil, compared with 1,237 population controls from the same locations. They found that daily cannabis users had more than threefold higher odds of psychotic disorder, compared with individuals who had never used cannabis (odds ratio, 3.2; P less than .0001), even after adjusting for sociodemographic factors and use of tobacco, stimulants, ketamine, and hallucinogenics.
Those who reported using high-potency cannabis (delta 9-tetrahydrocannabinol greater than or equal to 10%)--also showed a significant 60% increase in the odds of psychotic disorder, compared with never-users, which decreased slightly to 50% after controlling for daily use.
"The large sample size and the different types of cannabis available across Europe have allowed us to report that the dose-response relationship characterizing the association between cannabis use and psychosis reflects not only the use of high-potency cannabis but also the daily use of types with an amount of THC consistent with more traditional varieties," wrote Dr. Di Forti, of King's College London, and her coauthors.
The authors calculated that 12.2% of cases of first-episode psychosis would be avoided if high-potency cannabis were not available.
Individuals who started using cannabis at or before 15 years of age had 60% higher odds of psychotic disorder, compared with never-users (P = .0122), while those who started using high-potency cannabis at that age had more than a doubling of risk (OR, 2.3).
Similarly, those who used high-potency cannabis on a daily basis had nearly fivefold higher odds of psychotic disorder, compared with never-users, while daily users of low-potency had a 2.2-fold increase in risk.
Researchers also examined patterns of cannabis use and psychotic disorder across the 11 sites, which included Amsterdam; London; Cambridge, England; Madrid; Palermo, Italy; Paris; and Ribeirao Preto, Brazil.
They noted that significant variations in the incidence of psychotic disorder were found across the study sites, and that those variations correlated with the prevalence of daily cannabis use.
London and Amsterdam, where daily use was the most common, had the highest adjusted incidence rates of psychotic disorder (45.7 cases per 100,000 person-years in London and 37.9 per 100,000 person-years in Amsterdam). In contrast, the incidence in Bologna, Italy --where daily use was less frequent was half that of London.
"Education is needed to inform the public about the mental health hazards of regular use of high-potency cannabis, which is becoming increasingly available worldwide," they wrote.
The study was supported by several entities, including the European Community's Seventh Framework Program and the Sao Paulo Research Foundation. Five authors declared personal fees and grants from pharmaceutical companies.
SOURCE: Di Forti M et al. Lancet. 2019 Mar 19. doi: 10.1016/S22150366(19)30048-3.
BY BIANCA NOGRADY
FROM THE LANCET
VIEW ON THE NEWS
Which comes first--psychosis or cannabis use?
EPIDEMIOLOGIC AND EXPERIMENTAL STUDIES generally have established a link between heavy cannabis use and psychosis. However, a long-running issue has been that, while cannabis use has increased in some populations, the rates of psychosis have not necessarily done the same. The results of this study go against that, suggesting that differing rates and intensity of cannabis use across Europe appear to correlate with differing rates of psychosis.
This does not necessarily imply causality. For example, genetic studies suggest that individuals predisposed to psychosis also may have a predisposition to use cannabis. Another possibility is that subclinical mental health issues existed in those participants before the start of cannabis use. The challenge, therefore, remains to identify which individuals are most at risk from psychosis related to cannabis use, and to develop strategies aimed at mitigating this risk.
Suzanne H. Gage, PhD, is affiliated with the department of psychological sciences at the University of Liverpool (England). These comments are adapted from an accompanying editorial (Lancet. 2019 Mar 19. doi: 10.1016/ S2215036630086-0). No conflicts of interest were declared.
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|Title Annotation:||ADULT PSYCHIATRY|
|Publication:||Clinical Psychiatry News|
|Date:||Apr 1, 2019|
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