Nov. 5 (Bloomberg) -- Pfizer Inc., the world's largest drugmaker, said it will quit testing an obesity drug similar to ones junked by other companies because winning U.S. approval would be too slow, expensive and risky.

Pfizer is unwilling to pour money into new human tests the U.S. Food and Drug Administration is likely to require, the New York-based drugmaker said today in a statement. The drug, known by the chemical name CP-945,598, was in the third of three stages of testing required for market clearance and could have had more than $500 million in annual sales, analysts said.

Pfizer is among the last drugmakers to abandon obesity medicines that block the same brain receptor that makes marijuana smokers hungry. Before Sanofi-Aventis SA's drug was rejected by the FDA in June 2007 and Merck & Co. quit developing its version last month, analysts estimated annual sales of the products would top $3 billion.

``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,'' said Martin Mackay, Pfizer's president of research, in the statement. ``As part of our ongoing portfolio prioritization, we will refocus research and development resources on high-priority therapeutic areas that address an unmet medical need and have a high probability for success.''

Studies by Merck, of Whitehouse Station, New Jersey, and Sanofi, based in Paris, found that their versions of the obesity drug may be linked to suicides and depression. Bristol-Myers Squibb Co., of New York, is the last major drugmaker still developing a similar medicine, according to Bloomberg data.

Sanofi halted all human trials of its obesity drug, Acomplia, after health authorities in countries including France asked that local tests be stopped. The requests came after European regulators last month deemed the pill too dangerous for sale.

To contact the reporter on this story: Shannon Pettypiece in New York at spettypiece@bloomberg.net

Last Updated: November 5, 2008 17:51 EST