NEW YORK - Merck & Co. said on Monday that patients on its experimental obesity drug lost more than twice as much weight as those on a placebo in a late-stage clinical study.

Patients on taranabant lost an average of 14.5 pounds compared with 5.7 pounds for those on a placebo after 52 weeks — a difference deemed statistically significant, Merck said in a statement.

Merck & Co. said it won't include higher doses of taranabant in future studies because they have been linked to increased rates of depression and other psychiatric side effects.

The company's late-stage trial tested 2-milligram, 4-milligram, and 6-milligram doses of taranabant compared with placebo. The drug met its goal of reducing patients' weight in a late-stage study, but patients taking the higher 4-mg and 6-mg doses experienced higher rates of depression, anxiety, and irritability.

"Based on the benefit-risk considerations and the lack of a substantial improvement in the efficacy of taranabant at the 4-milligram and 6-milligram doses seen in our clinical program compared to the 2-milligram dose, we have decided to continue to evaluate taranabant in doses up to and including 2 milligrams in our Phase III studies," said Dr. John Amatruda, vice president of clinical research, metabolic disorders, for Merck, in a statement.

The findings were presented at the American College of Cardiology conference in Chicago.

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