Marijuana, Schizophrenia and Reefer Madness

The government is going after marijuana because, they claim, it may lead to serious mental health problmes:

Youngsters who use marijuana are more likely to develop serious mental health problems, the government said Tuesday. . . .But questions remain about whether people who smoke marijuana at a young age are already predisposed to mental disorders, or whether the drug caused those disorders

My initial reaction is great skepticism; my general sense is that the anti-drug establishment is cavalier with its claims of harm, particularly from marijuana (I am not a regular user of any illegal drugs, so I don't have a particular axe to grind; I do use alcohol and caffeine regularly) which I generally regard as on par with alcohol as far as safety and probably better than tobacco. As I'm generally libertarian, I have been in favor of marijuana decrimilization, but it is not a big issue for me*.

But I remembered an interesting article (not free except subscribers, I think) I saw about the issue that swayed me a bit. Published in BMJ this January, it involves nearly 2500 Germans age 14-24. Predispositon to psychosis and marijuana use were measured at baseline and then development of psychosis and current marijuana use were measured four years later.

As had been shown in other studies, pot use increased the risk of psychosis. But it is always hard to know whether this represents an effect of the marijuana or just self-treatment by those predisposed to psychosis. In other words, people who are going to be psychotic may already have mild, sub-clinical symptoms and use marijuana to treat them.

What made this study better and more convincing was that they showed that the increased risk from marijuana use was much higher in those predisposed to psychosis. That is, those identified at "high risk" at baseline who smoked pot had a greatly increased risk of psychosis compared to those at risk who didn't. Those not identified at risk had only a small increase. Further, the "at risk" assesment at baseline did not predict use of marijuana at follow up, which argues against the self-medicating hypothesis. Not conclusive, but suggestive. The article also discusses colocalization of cannibis and dopamine receptors in the brain (dopamine is dysregulated in schizophrenia and other psychoses).

Legalization advocates criticize this and similar studies as association, not causation and on a variety of other grounds. I can't help but feel, that, in reverse of the usual situation, it is the pro-marijuana argument that relies on distortion and half-truths in this case

Now as the original article points out, whether a slightly increased risk of schizoprhenia justifies all the social costs of the war on marijuana is still an open question


*It occurr to me than marijuana decrimilization/legalization faces a significant problem: those who smoke regularly are unlikely to have the energy and initiative to effectively advocate for legalization and those (like me) who don't smoke but are in principle are in favor are unlikely to care enought about the issue to do so.