The Food and Drug Administration has approved Arena Pharmaceutical's anti-obesity pill Belviq, the first new prescription drug for long-term weight loss to enter the U.S. market in over a decade.

Despite only achieving modest weight loss in clinical studies, the drug appeared safe enough to win the FDA's endorsement, amid calls from doctors for new weight-loss treatments.

The agency cleared the pill Wednesday for adults who are obese or are overweight with at least one medical complication, such as diabetes or high cholesterol.