As we continue to move down the road to legalizing cannabis for medicinal and recreational use, we must also continue to research its effects—both the potentially therapeutic and the potentially harmful.
For years there has been a perceived link between marijuana use and the development of psychotic symptoms. Though an association has been seen, there have been limitations in the studies done to date.
We have not been able to determine whether a prior history of regular cannabis use increases an adolescent’s risk of experiencing persistent psychotic symptoms even after drug use has stopped for several months or years.
Also, it has been unclear whether the association between adolescent marijuana use and later psychotic symptoms is actually causal or a function of other factors. Some wonder whether cannabis causes symptoms or whether people already with those symptoms are more likely to attempt to self-medicate with cannabis.
A study published in May examined this relationship in more than 1,000 adolescent boys to determine whether those with regular marijuana use had a systemic increase in psychotic symptoms that persisted even during periods of abstinence from cannabis use.
Results found that regular adolescent marijuana use may significantly increase the likelihood of developing persistent psychotic symptoms.
For each year adolescent boys regularly used marijuana, their expected level of psychotic symptoms rose by 21 per cent, their odds of experiencing paranoia went up 133 per cent, and hallucinations 92 per cent. Further, the effect of marijuana use on psychotic symptoms persisted even when the teens stopped using the drug for a year.
No support was found for the self-medication theory—the subjects were not more likely to use marijuana after their psychotic symptoms increased.
This is a good step forward in our understanding of the relationship between marijuana use and the development of psychotic symptoms and disorders. However, more research is needed. For example, this study examined only boys from one geographic region. Future studies should look at girls as well and a variety of environments.
Future research should also examine how many individuals with psychotic symptoms went on to develop full-blown psychotic disorders in adulthood and whether linkages remain important after accounting for other factors.
What we can see though is that there does seem to be a causal relationship between regular marijuana use during adolescence and the development of psychotic symptoms that can persist even after drug use has stopped. This should be considered when we give young people information about recreational or medicinal use of this product.