Drug safety is hard

There are new reports, according to the Herald, that synthetic cannabinoids are ‘associated’ with suicidal tendencies in long-term users.  One difficulty in evaluating this sort of data is the huge peak in suicide rates in young men.  Almost anything you can think of that might be a bad idea is more commonly done by young men than by other people, so an apparent association isn’t all that surprising.  There is also the problem with direction of causation — the sorts of problems that make suicide a risk might also increase drug use — and difficulties even in getting a reasonable estimate of the denominator, the number of people using the drug. Serious, rare effects of a recreational drug are the hardest to be sure about, and the same is true of prescription medications.  It took big randomized trials to find out that Vioxx more than doubled your rate of heart attack , and a study of 1500 lung-cancer cases even to find the 20-fold increase in risk from smoking.

In this particular example there is additional supporting evidence. A few years back there was a lot of research into anti-cannabinoid drugs for weight loss (anti-munchies), and one of the things that sank these was an increase in suicidal thoughts in the patients in the early randomized trials.  It’s quite plausible that the same effect would happen as a dose of the cannabinoid wears off.

In general, though, this is the sort of effect that the proposed testing scheme for psychoactive drugs will have difficulty finding, or ruling out.