The U.S. Food and Drug Administration (FDA) on Wednesday approved Belviq to treat obesity, making it the first new weight-loss drug in 13 years.

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

BMI, which measures body fat based on an individual's weight and height, is used to define the obesity and overweight categories. According to the Centers for Disease Control and Prevention, more than one-third of adults in the United States are obese.

"Obesity threatens the overall well being 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."

Belviq works by activating the serotonin 2C receptor in the brain. Activation of this receptor may help a person eat less and feel full after eating smaller amounts of food.

The safety and efficacy of Belviq were evaluated in three randomized, placebo-controlled trials that included nearly 8,000 obese and overweight patients treated for 52 to 104 weeks. All participants received lifestyle modification that consisted of a reduced calorie diet and exercise counseling. 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.

The most common side effects of Belviq in non-diabetic patients are headache, dizziness, fatigue, nausea, dry mouth, and constipation, and in diabetic patients are low blood sugar ( hypoglycemia), headache, back pain, cough, and fatigue.

Belviq is manufactured by Arena Pharmaceuticals of Switzerland.