French drug maker Sanofi-Aventis and Pfizer Inc. both separately announced their decision to halt all research on experimental drugs for obesity. Both the obesity drugs work by blocking the cannabinoid type 1 pleasure centers in the brain and have been discontinued because of side effects uncovered in clinical trials.

Earlier this month Merck & Co. said it was stopping research on taranabant, its experimental obesity drug. Obesity is possibly the world’s biggest health issue and stopping the drugs would mean the end to sure sales in this category for New York based, Pfizer, the world’s largest drug maker and Paris-based Sanofi-Aventis, ranked No. 4.

Analyst Steve Brozak of WBB Securities said, "This will significantly affect the perception of their (future) revenues." He added that Pfizer is technically correct in stating that even if the drug is safe, it's not certain that it could make it onto the U.S. market because the FDA "has almost become paralyzed with caution in its approval process."

Martin Mackay, Pfizer research chief said in a statement, "While confident in the safety of the compound, we believe that this is the appropriate decision based on all available information regarding this class of agents, as well as recent discussions with regulatory authorities." The statement said the company believes the compound "has the potential to be a safe and effective treatment for weight management."

The drugs have been linked to psychiatric side effects, including mood disorders and neurodegenerative disorders such as multiple sclerosis. Till four years ago Acomplia was being touted as a pill that could help people lose weight, control blood sugar and other aspects of diabetes, lower cholesterol, quit smoking and stop abusing alcohol, marijuana and cocaine.

In Europe between June and August 2008 there were five suicides among participants in the trial who took the drug, compared to one among those taking a placebo, which led to European regulators calling for the drug to be withdrawn. The agency had concluded that "the benefits of Acomplia no longer outweigh its risk."

In a statement the company said it was stopping ongoing human testing of Acomplia, known chemically as rimonabant, for all uses, "in light of recent demands by certain national health authorities."

Pfizer said it ended final-stage human testing because of "changing regulatory perspectives on the risk/benefit profile of the CB1 class and likely new regulatory requirements for approval."