The decline and fall of the cannabinoid antagonists

Cannabinoid Receptor, Type 1 (CB1) antagonists were supposed to be the next big thing. They're weight loss drugs, and with obesity rates rising and the diet craze showing no signs of abating, that's a large and growing market (...sorry). They worked, at least in the short term, and they were at least as effective as existing pills...

But it ended in tears, literally. Rimonabant was pulled from the European market in late 2008; it was never approved in the USA at all. After rimonabant was withdrawn, drug companies abandoned the development of other CB1 antagonists.

The problem was that they made people depressed. In several large clinical trials of rimonabant it raised the risk of suffering depression and other psychiatric problems, like anxiety and irritability, compared to placebo. The reported rates of these symptoms ranged from a few % up to over 40% depending upon the population, but there have been no trials (except very small ones) in which these effects weren't seen. This means that CB1 antagonists cause depression rather more consistently than antidepressants treat it...

There were side effects. Alongside things like nausea, vomiting, and sweating, about 35% of people taking high doses of taranabant reported "psychiatric disorders". 20% of people on placebo also did, so this is not quite as bad as it first appears, but it's still striking, especially since a number of people on high doses of taranabant reported suicidal thoughts or behaviours...

Yes, people who take the anti-pot (cannabinoid antagonists) feel depressed and want to kill themselves. But at least they lose weight; call it the anti-munchies. Designer cannabinoids may be an untapped market, but anti-cannabis just seems wrong. This smelled like a bad idea from the start.

[Thanks Jonathan!]