Merck & Co. has decided to bring to an end the development the experimental obesity drug taranabant on account of its many adverse events, a statement from the company says.

The pharmaceutical company said on Thursday that the efficiency and side-effects are conditional on dose levels, which means that higher doses of the drug lead to a greater effectiveness but also to an increased number of side-effects. Basically, the drug maker couldn’t find a dose level that would help people lose weight and, at the same time, pose minimal risk to their health.

Although Merck said taranabant did his job and helped individuals in the fight against obesity, there have also been reported several psychiatric events linked to the intake of the drug.

The weight loss drug taranabant, which acts on cannabinoid receptors, belongs to the same class of drugs as Sanofi-Aventis's Acomplia, a slimming pill for obesity treatment which didn’t receive the Food and Drug Administration approval to be allowed in the US market seeing that data from clinical trials suggested it may increase the risk of suicide.

The company’s discontinuation of taranabant emphasizes the difficulty raised by developing an effective drug able to help people lose weight.

Merck took the decision of stopping the development of the anti-obesity drug following the results of the last phase of human testing for regulatory approval. "Available Phase III data showed that both efficacy and adverse events were dose related, with greater efficacy and more adverse events in the higher doses," said John Amatruda, Merck's senior vice president and research head for diabetes and obesity.