Weight loss medications are prescribed only as a component of a weight loss program that includes a healthy low-calorie diet and regular physical activity. On average, people on prescription weight loss drugs lose about 5-10% of their original weight. They may lose in the range of 4.4-22 lb (2-10 kg) above what they might have lost following a diet and exercise program alone. Patients who lose weight initially on a drug tend to continue to respond. However, those who fail to lose 4 lb (2 kg) within the first month on a weight loss medication are unlikely to respond to that particular drug even at an increased dosage. Over-the-counter weight loss drugs have been found to be ineffective, unsafe, or both.
Most weight loss occurs within the first six months of drug use, after which the weight levels off or increases. The majority of patients regain the lost weight after discontinuing the medication. Thus short-term use of weight loss drugs may not be beneficial. However, long-term use of weight loss drugs may help maintain the lower weight. Since obesity is a chronic disorder, treatment must be continued for years or for life. However, as of 2005, sibutramine (Merida) and orlistat (Xenical) were the only weight loss drugs approved by the U. S. Food and Drug Administration (FDA) for use for more than a few weeks.