The US’s Food & Drug Administration has refused permission for the manufacturers of Lorcaserin, a new diet pill, to put it on the market.

The FDA told Arena Pharmaceuticals this was because of concerns about its marginal effectiveness and about cancers that occurred at higher-than-usual rates during clinical trials with rats. The FDA’s decision comes just two weeks after the makers of the prescription diet-pill Meridia was banned in the US and Canadian markets at the request of the FDA.

Lorcaserin was developed by Arena Pharmaceuticals, the San Diego drug company in partnership with Eisai Co.

Among the FDA’s concerns were weight-loss results that failed to rise to the FDA’s standards for approval, and an  increase in cancerous breast and brain tumors in rats that were given a dose of the drug that is higher than that proposed for humans.

A clinical trial of Lorcaserin published in the New England Journal of Medicine found that two-thirds of patients lost at least 5% of their body weight, while a third lost at least 10% of body weight, with an average loss of 17 to 18 pounds.