The US Food and Drug Administration 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 US Food and Drug Administration today approved Belviq (lorcaserin hydrochloride), as an addition to a reduced-calorie diet and exercise, for chronic weight management," it said in a statement.

The drug works to control the appetite through receptors in the brain by activating the serotonin 2C receptor.

Trials showed the drug helped patients lose an average of three to 3.7 percent of their body weight after a year when compared to a placebo, the FDA said.

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

"Obesity threatens the overall wellbeing of patients and is a major public health concern," said Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research.

"The approval of this drug, used responsibly in combination with a healthy diet and lifestyle, provides a treatment option for Americans who are obese or are overweight and have at least one weight-related comorbid condition."

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.

The FDA said it would require Arena Pharmaceuticals ― which has offices in San Diego, California and Zofingen, Switzerland ― to conduct conduct six future postmarketing studies to assess risks such as heart attack and stroke.

The label will also recommend that Belviq be discontinued in patients who fail to 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 should not be used by pregnant women and may cause serious side effects of 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.

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 percent."(WASHINGTON=AFP)