One year ago millions of obese Americans were waiting to hear whether or not the Food and Drugs Agency would give approval to the diet drug rimonabant, banded as Acomplia in Europe. Obviously there was huge disappointment when this approval was not given. Rimonabant never actually made it to the American market although it is thought that the patent holder will return for another bite of the cherry at a later date, armed with deeper clinical trial data.

There is, therefore, a great deal if excitement over Merck’s new diet drug taranabant. The results from the second phase of testing were encouraging and now after another two years of testing it seems that the results for phase three may be equally exciting, though the final report is yet to be published.

Researchers announced that study participants taking varying doses of taranabant lost 8 to 14 pounds over a 12-week period. There was one question, however, which still remains unanswered. Does taranabant have less significant side effects than rimonabant? Both drugs work in a similar way, by targeting particular receptors in the brain. Acomplia, however, was not approved by the FDA after concerns were raised over its psychiatric side effects which may include depression and suicidal thoughts in patients prone to mental health problems. So how does taranabant compare? Initial feedback seems to suggest that between one-fifth and one-third of patients had experienced adverse side effects which included depressed mood, irritability, anger, mood swings and insomnia. Unlike rimonabant, however, patients reported no suicidal thoughts though it was conceded that the question had not been asked in a systematic way.

There will, of course, have to be more conclusive evidence provided before the FDA grants approval to the new drug. The company expects the phase III report to be published later this year and for taranabant to be submitted for FDA approval before the end of 2008. Taranabant will also be submitted to the European Medicines Agency although it is believed that Merck wants to get it approved in the US first.