Belviq, made by Arena Pharmaceutical, can be used by obese or overweight adults with at least one condition.
The drug achieved only modest results in clinical studies, helping people lose on average about 5% of their body weight.
Belviq was rejected in 2010 because of concerns over tumours that developed in animals tested with the drug.
After San Diego-based Arena resubmitted its application with more data, the US Food and Drug Administration (FDA) found little risk of tumours in humans using the drug.
The medication is expected to launch in 2013.
Belviq is designed to block appetite signals in the brain, making patients feel fuller with smaller amounts of food.
It has been approved for use in obese adults with a body mass index of 30 or greater.
The drug can also be used by overweight adults with a BMI of 27 or greater if they have at least one other condition such as high blood pressure, type 2 diabetes or high cholesterol.
The FDA warned that Belviq is not for women who are pregnant or nursing.
Arena will be required to conduct six studies after marketing the drug, including a study on the drug’s effect on long-term heart health.