The experimental med may help people lose some weight, but the side effects are the same ones that sunk Sanofi-Aventis diet drug last year. The findings were seen in mid-stage trials of Merck’s taranabant and reported in the latest issue of Cell Metabolism. The pill is currently being tested in a far larger late-stage trial and results are expected later this year. Like Sanofi-Aventis’s Acomplia, taranabant works by blocking cannabinoid receptors in the brain, and these are the same receptors that give people the munchies when smoking marijuana, by the way.

One of the Phase II trials involved 553 obese patients who were tested for 12 weeks, Reuters writes. Patients receiving varying doses of the Merck drug lost 8 to 14 pounds of body weight, which compared favorably with weight losses seen in separate and far longer late-stage trials of Acomplia, which is sold in some overseas markets. Still, there psychiatric problems “reminiscent” of those seen in Acomplia, such as depression, anxiety and irritability.

“Although the trends in these and related factors were small and not statistically reliable, any increase in incidence would have potentially immense clinical significance when multiplied across a potential patient population of many millions,” the article said. An FDA advisory panel last June recommended that Acomplia not be approved because it may increase suicidal thoughts and depression. Sanofi-Aventis later gave up on seeking approval.

In a separate 24-hour food-intake study described in the Cell Metabolism article, a 12-milligram dose of taranabant cut calorie intake by about 20 percent, compared with placebo, while a related study showed a modest increase in energy expenditure. Merck said a considerably smaller dose is being tested in the ongoing Phase III trial. “In doses we’re studying, we believe the drug can be effective in weight loss, yet be safe,” Merck spokeswoman Amy Rose tells Reuters.

She cautioned that favorable weight-loss trends seen in the mid-stage studies must be confirmed by the larger Phase III trial and that safety must be explored further. “There is so much hype about obesity and weight-loss treatments in general; we need to wait for reliable data,” says Rose, adding that much of the data from the Phase II studies was presented in October at a medical meeting in New Orleans.