Whitehouse Station, NJ - Merck & Co announced today that it is stopping late-stage clinical development of taranabant, an investigational cannabinoid-receptor blocker being tested for the treatment of obesity, and will not seek regulatory approval for the agent [1].

The company released a short, two-paragraph statement saying that the "the overall profile of taranabant does not support further development for obesity."

Prospects for the drug did not look good, as there was evidence of psychiatric and gastrointestinal side effects in phase 3 clinical trials for weight loss. As reported by heartwire this past April, adverse events were greater at the highest doses of taranabant, with roughly 45% of patients taking 4-mg and 6-mg doses experiencing gastrointestinal side effects, and 40% of patients experiencing psychiatric side effects, such as an increase in anxiety, irritability, and depressed mood.

Taranabant is similar to rimonabant (Acomplia, Sanofi-Aventis), another cannabinoid antagonist currently on the market in Europe. This past June, however, new data from the UK's Medicines and Healthcare Products Regulatory Agency showed that it too might pose a risk, with rimonabant associated with five deaths in the UK since its launch in mid-2006. Sanofi-Aventis said three of the deaths were of cardiac origin (two MIs and one sudden death), one was the result of an infection, and one of psychiatric causes.

The Food and Drug Administration unanimously rejected approval of rimonabant for obesity in June 2007.