Just wanted to share some quick thoughts on a large meta-analysis that was recently published in the prestigious Archives of General Psychiatry. In this publication, the authors reviewed all previous studies that have examined the association between substance use (Cannabis, Alcohol, and other substances) and the onset of psychotic disorders (such as schizophrenia). Although the research on the potential harmful effects of pot use is quite controversial in many issues (e.g., whether pot is a gateway drug or not*), one finding that appears to be more consistent is that the use of cannabis is related to an earlier onset of psychotic disorders. This meta-analysis was intended to examine the results of all previous studies using statistical techniques that allow the researchers to reach some conclusions about what previous studies, as a whole, truly say about this topic.
The meta-analysis included 83 different studies with a total of 8,167 substance-using patients and 14,352 non-substance using patients. Note that both samples (substance and non-substance using) were patients with a confirmed diagnosis of a psychotic disorder. The study then compared the age of onset of the condition between the substance vs. non-substance using groups.
- The age of onset of the psychosis for cannabis users was 2.70 years younger than non-substance users.
- The age of onset of the psychosis of other (non-pot and non-alcohol) users was also 2 years younger than non-substance users.
- The age of onset of alcohol users was not different than the age of onset of non-users.
However, these results do not address a basic question regarding the association of pot use and psychosis: Does pot use CAUSE an early onset of psychosis OR are those with early onset more likely to have used pot for other reasons (e.g., self-medication). The authors dispute this idea because they did not find alcohol to be related to earlier onset. I’m not sure that argument is convincing because it is still possible that youth in early stages of psychosis find cannabis use to provide a function (self medication) that alcohol does not. It is also possible that cannabis and other drug users simply raise alarms with family and friends earlier leading to faster identification and diagnosis (e.g., reflected in “earlier onset”) than non-substance users. In addition, we do not know whether those who had early onset and were pot users would have developed psychosis a bit later had they not been using pot. So these results are intriguing but the nature of the association between cannabis use and psychosis is still a bit unclear.
* Studies consistently show that most people who use hard drugs had used cannabis before starting hard drugs BUT most cannabis users never go on to use hard drugs.
The reference: Large, M., Sharma, S., Compton, M., Slade, T., & Nielssen, O. (2011). Cannabis Use and Earlier Onset of Psychosis: A Systematic Meta-analysis Archives of General Psychiatry DOI: 10.1001/archgenpsychiatry.2011.5