Pfizer Inc., the world's largest drug maker, became the latest company to abandon a treatment for its experimental obesity drug.  The drug CP-945,598, works by blocking receptor in the brain that makes people hungry after smoking marijuana and falls into the same class of other drugs linked to psychiatric side effects. The class of drugs, known as cannabinoid receptor antagonists, has been linked to psychiatric side effects, such as depression and suicidal thoughts and the FDA has expressed concerns that blocking the same chemical could increase the risk for other problems, including mood disorders and neurodegenerative disorders such as multiple sclerosis.

Pfizer said it was terminating late stage development of the drug citing "changing regulatory perspectives" and problems seen with other medicines from the same class as well as the possibility of tougher requirements by the Food and Drug Administration.

In an announcement made earlier, Pfizer had announced that obesity was one of the areas it would no longer pursue its research in though they would continue to work on the medicines which were in Phase III of development. Phase III is the final stage of human testing before seeking an approval decision.

Martin Mackay, Pfizer president of global research and development 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 drug CP-945,598 falls into the same category as Sanofi Aventis SA's   rimonabant, which was never approved for use in the U.S. Merck & Co also stopped development of its drug taranabant which was linked to psychiatric side effects in clinical studies.