Diet drug taranabant, a CB-1 receptor inverse agonist which many hoped would have a better side-effect profile than Sanofi's CB-1 receptor antagonist rimonabant (Acomplia / Zimulti), may have similar problems, according to an analyst for investment bank Leerink Swann.

Analyst Aileen Salares, in a research report based on an abstract of data from the two-year Phase III trial of taranabant, said the diet drug did not live up to expectations and had worse psychiatric and neurological side effects than anticipated

Taranabant's developer, Merck, which submitted the abstract of data from the Phase III trial in advance of the annual scientific meeting of the American College of Cardiology scheduled for later this month in Chicago, said it could not comment on the study until the data is formally presented.

But Salares said the 2 milligram dose of the taranabant -- the dose many observers expected to be submitted later this year to the FDA -- produced only a 4 percent weight loss, failing to reach FDA's 5 percent weight-loss threshold for approval of a new diet drug.

She added that the safety profile of the 2 milligram dose of the drug was "not nearly as clean as expected" with twice as many participants dropping out of the trial because of psychiatric side effects as patients taking a placebo.

The side effects included suicidal thoughts reminiscent of the psychiatric side-effects which led to the decision by an FDA advisory panel last summer to unanimously recommend against approval of rimonabant.

While a higher 4 milligram dose of taranabant also tested in the Phase III trial achieved the desired 5 percent weight loss, Salares said it was associated with a considerably higher incidence of psychiatric side effects than the 2 milligram dose.