SAN DIEGO ( TheStreet) -- The efficacy of Arena Pharmaceuticals' ( ARNA) weight-loss drug lorcaserin is still marginal but now the drug may also be unsafe.

That's my read of a new lorcaserin study in diabetes patients released by Arena Tuesday morning. U.S. regulators rejected lorcaserin in October, calling the drug's ability to help obese patients lose weight "marginal." Nothing in the just-announced "BLOOM-DM" data is going to change that perception.

Alarmingly, however, lorcaserin's relatively clean heart safety profile from prior phase III studies takes a hit in the BLOOM-DM study, with almost six times as many lorcaserin patients reporting new cases of heart valve damage compared to patients treated with placebo after one year.

Arena shares closed Monday at $1.53.

The BLOOM-DM study enrolled just over 600 patients who were obese and suffered from Type 2 diabetes. Patients were treated with either lorcaserin twice daily or a placebo and followed for 52 weeks.

Lorcaserin patients reported a mean weight loss of 4.5% compared to 1.5% weight loss for placebo patients. The 3% weight loss (placebo adjusted) for lorcaserin is slightly worse than the 3.1% and 3.6% mean weight loss results (also placebo adjusted) from the two prior phase III studies. The result also falls below one of two minimum efficacy standards for weight-loss drugs set by FDA.

Diabetics have a hard time losing weight, so efficacy results from the Bloom DM study were not expected to be as robust.

After one year, 37.5% of lorcaserin patients lost at least 5% of their body weight compared to 16.1% of placebo-treated patients. This result satisfies one of the FDA's efficacy's standards for new weight-loss drugs.

Lorcaserin didn't do much to help patients resolve other diabetes-related health issues either. Lorcaserin-treated patients were able to reduce blood glucose levels by 0.5% (placebo adjusted) but changes in fasting insulin, triglycerides, total cholesterol, HDL cholesterol, LDL cholesterol, and systolic and diastolic blood pressure were not statistically significant.

On the safety side of the BLOOM-DM study, 2.5% of lorcaserin-treated patients reported new cases of valvulopathy, or heart-valve problems, compared to 1.9% of placebo patients after six months of treatment.

Measured at one year, 2.9% of lorcaserin patients reported new valvulopathy but the rate for placebo-treated patients fell to 0.5%.

Arena said the BLOOM-DM study was not designed to "detect meaningful differences in the incidence of valvulopathy." The company did not, however, offer an explanation for why the rates of valvulopathy were numerically higher in the lorcaserin-treated patients.

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