Sanofi-Aventis and Pfizer are the latest in the list of pharma companies to stop development of a class of anti-obesity drugs that were thought to have excellent potential.

Both companies have announced the termination of further development for their pipeline drugs in the cannabinoid 1 (CB1) receptor antagonist class, which were in clinical trials. The companies’ disclosures come close on the heels of Merck & Co, which discontinued development of Taranabant, its most advanced antiobesity agent, as data from Phase III trials showed that in addition to having greater efficacy at higher doses, the drug also produced more adverse effects.

The company said, “after careful consideration, we determined that the overall profile of Taranabant does not support further development for obesity.”

Analysts say that it will be difficult for other companies which have potential drugs in the class to carry on now. They say other companies will certainly feel the challenge of passing through the regulatory processes with this class of drugs.

Other companies that have advanced CB1 receptor antagonists in development are Bristol-Myers Squibb and Solvay’s Ibipinabant and AZD-2207 from AstraZeneca, which are both in mid-stage Phase II tests.

On November 5th, Sanofi formally said they would not continue with the development of Acomplia, which had been seen as one of its biggest drug hopes. It discontinued all trials of the drug, including those in diabetes. Pfizer also announced that it was terminating late-stage development of its experimental obesity drug Otenabant. The Acomplia website, which says it has no relation to Sanofi Aventis, said, “Sanofi have stopped research into Acomplia, so it is unlikely that it will be approved for use in the UK and Europe again.”

In the past Acomplia was introduced on the website like this: “If you, like millions of people around the world, struggle to keep your weight down, you cannot fail to have heard about Acomplia, purported to be the new wonder slimming drug.”

Research has said that CB1 drugs work by blocking the same receptors in the brain that make people hungry after smoking marijuana. However, they have also been linked to side-effects, such as depression and suicidal thoughts.

Further Reading:

Anti-Obesity Biologics- Competitor Analysis

Rimonabant: The first of the Cannabinoid blockbusters