WASHINGTON: US regulators on Wednesday approved the first drug to treat obesity in 13 years, a drug called lorcaserin, marketed as Belviq and made by Arena Pharmaceuticals.

The drug works to control the appetite through receptors in the brain and was approved as additional therapy for certain overweight and obese patients, combined with diet and exercise.

Trials showed the drug helped people lose an average of three to 3.7 per cent of their body weight after a year when compared to a placebo, the US Food and Drug Administration said.

It is approved for use in obese adults with a body mass index of 30 or greater, or overweight adults with a BMI of 27 or greater who have at least one other condition such as high blood pressure, type 2 diabetes, or high cholesterol.

Arena's stock opened the day at $9 per share and jumped as high as 47 percent on news of the US approval. The company said it is also seeking approval on the European market, but has no timeline yet for a decision.

Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, described obesity as “a major public health concern,” and said the new drug offers a treatment option when used “responsibly in combination with a healthy diet and lifestyle.”

However, the FDA warned that Belviq is not for women who are pregnant or nursing, and called for further long-term postmarketing studies on the drug's potential risks.

The label will also recommend that Belviq be discontinued in patients who fail to lose five percent of their body weight after 12 weeks of treatment.

“These patients are unlikely to achieve clinically meaningful weight loss with continued treatment,” said the FDA statement.

Belviq activates the serotonin 2C receptor in the brain, and may cause serious side effects if taken in combination with certain medications for depression and migraine that increase serotonin levels or activate serotonin receptors.

“Belviq may also cause disturbances in attention or memory,” said the FDA.

Common side-effects in patients without diabetes include headache, dizziness, fatigue, nausea, dry mouth, and constipation.

In diabetic patients, side effects may include low blood sugar, headache, back pain, cough, and fatigue.

Lorcaserin was rejected in 2010 by the Endocrinologic and Metabolic Drugs Advisory Committee, which advises the FDA, over concerns that it formed breast tumors in rats.

But those effects did not appear in trials on overweight and obese humans.

An independent advisory committee to the FDA recommended the drug be approved in May after three randomized, placebo-controlled trials of nearly 8,000 patients spanning one to two years.

“All participants received lifestyle modification that consisted of a reduced calorie diet and exercise counseling,” the FDA said.

“Compared with placebo, treatment with Belviq for up to one year was associated with average weight loss ranging from three percent to 3.7 per cent.”

Some patients with type 2 diabetes experienced higher levels of weight loss, with 38 percent of these patients achieving at least five percent loss of their body weight compared to 16 percent who did the same on a placebo.

The pills will be manufactured at Arena's facility in Zofingen, Switzerland, and will be distributed in the US by Eisai Pharmaceuticals.

Arena is headquartered in San Diego, California.

According to Michael Aziz, internist at Lenox Hill Hospital in New York City, the biggest apparent drawback to the drug is the tiny amount of weight loss that patients experience while taking it.

“The only problem with this drug is the weight loss is so, so very low,” Aziz told AFP, remarking that a 200 pound (91 kilogram) person might lose just six pounds (2.7 kg) in a year, based on the study data.

“That is so insignificant,” he said. “I think people should also implement lifestyle changes because the fact is, people can lose one pound a week and that is perfectly healthy.”

The last anti-obesity drug approved in the United States was Xenical (Orlistat) by Roche in 1999.

Sold over the counter as Alli by GlaxoSmithKline, it works by preventing the body from absorbing fat, though its tendency to cause gastrointestinal side effects such as oily, loose stools have curbed its popularity among patients.