The first new prescription diet drug in 13 years won Food and Drug Administration (FDA) approval on Wednesday, offering a new alternative to aid weight loss for the nearly one in three Americans who are considered obese. The new drug, called Belviq (lorcaserin), is made by Arena Pharmaceuticals. Here’s what you need to know:
How does Belviq work?
The drug works by controlling appetite — specifically by activating brain receptors for serotonin, a neurotransmitter that triggers feelings of satiety and satisfaction. Serotonin is also involved in mood; many antidepressant drugs work by preventing the reuptake of serotonin and keeping brain receptors bathed in the chemical. Researchers at Arena say their drug is designed to seek out only the serotonin receptors that affect appetite.
How effective is it?
According to clinical trial data submitted by Arena to the FDA, nearly half of dieters without Type 2 diabetes who used the medication lost at least 5% of their starting weight — or an average of 12 lbs. — over a year, compared with 23% of those taking a placebo. For best results, dieters are advised to use the medication together with a healthy diet and exercise program. The approved labeling for Belviq also recommends that people discontinue the drug if they fail to lose 5% of their body weight after 12 weeks; longer treatment is unlikely to lead to meaningful weight loss.
(MORE: Calorie vs. Calorie: Study Evaluates Three Diets for Staying Slim)
Who can take Belviq?
The FDA approved the medication for people who are obese (with a body mass index, or BMI, of 30 or higher) or who are overweight (with a BMI of 27 or above) and also have at least one weight-related health condition such as Type 2 diabetes, high blood pressure or high cholesterol.
Are there any side effects?
The most common side effects of Belviq in non-diabetic patients are headache, dizziness, fatigue, nausea, dry mouth and constipation; in patients with diabetes, side effects include low blood sugar, headache, back pain, cough and fatigue.
There was also some concern that Belviq caused tumors in animals and heart-valve defects in people. A similar serotonin-based drug that had been approved for weight loss — fenfluramine — was removed from the market in 1997 because of the same heart concerns.
In 2010, the FDA rejected Arena’s first request for approval, asking for more evidence of its safety. New data provided by the company showed that heart problems would not occur at the low doses at which Belviq would be prescribed. The FDA won’t require patients taking Belviq to be monitored for heart-valve damage, but the company is required to conduct six studies once the drug reaches the market to determine whether it causes heart attacks or stroke in people who take it.
(MORE: A Brief History of Diet Pills and the FDA)
Why did it take so long to get a new weight-loss drug approved?
The history of diet pills has been plagued by safety problems. Since 1999, when the last prescription weight-loss medication, Xenical (orlistat), was given the green light, one weight loss drug, Meridia (sibutramine) was taken off the market when users began showing increased risk of heart problems, and two others, Belviq and Qnexa, were rejected by the FDA over safety concerns. Manipulating the body’s weight-controlling pathways can have long-term consequences on the heart and other metabolic systems, so drug developers have a high bar to clear to prove their compounds are safe.
Read the FDA’s announcement on Belviq here.
Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.