Common weight-loss drugs

Diethylpropion (Tenuate) and phentermine (Adipex) are approved by the Food and Drug Administration (FDA) for only short-term use — generally less than 12 weeks. Orlistat (Xenical), lorcaserin (Belviq) and a combination drug (Qsymia) are approved by the FDA for long-term use. Qsymia contains phentermine and an extended-release (ER) form of topiramate. Orlistat is also available in a reduced-strength form without a prescription (Alli).

The chart shows the commonly used prescription weight-loss drugs, how they work and their side effects.

DrugMechanism of actionPossible side effects
Benzphetamine (Didrex) Decreases appetite, increases feeling of fullness Increased blood pressure and heart rate, nervousness, insomnia, dry mouth, constipation
Diethylpropion (Tenuate) Decreases appetite, increases feeling of fullness Increased blood pressure and heart rate, nervousness, insomnia, dry mouth, constipation
Lorcaserin (Belviq) Decreases appetite, increases feeling of fullness Increased heart rate, headache, dizziness, nausea
Phendimetrazine (Bontril) Decreases appetite, increases feeling of fullness Increased blood pressure and heart rate, nervousness, insomnia, dry mouth, constipation
Phentermine (Adipex, Suprenza) Decreases appetite, increases feeling of fullness Increased blood pressure and heart rate, nervousness, insomnia, dry mouth, constipation
Orlistat (Xenical) Blocks absorption of fat Intestinal cramps, gas, diarrhea, oily spotting
Phentermine and extended-release topiramate (Qsymia) Decreases appetite, increases feeling of fullness Increased heart rate, birth defects, tingling of hands and feet, dry mouth, constipation, anxiety

Safety of weight-loss drugs

Diethylpropion (Tenuate), phentermine (Adipex), benzphetamine (Didrex) and phendimetrazine (Bontril) are approved for only short-term use — generally less than 12 weeks. These drugs are classified as controlled substances because they have the potential to be abused. Because of possible side effects, these drugs aren't recommended if you have heart disease, high blood pressure or hyperthyroidism.

Orlistat (Xenical), lorcaserin (Belviq) and phentermine-topiramate (Qsymia) are approved for long-term use. Orlistat is also available in a reduced-strength form without a prescription (Alli).

After orlistat was approved, rare cases of serious liver injury were reported in some people taking it. No cause and effect relationship was established between. However, Xenical and Alli labels now advise people taking orlistat to be alert to signs and symptoms that could indicate liver injury, such as itching, loss of appetite, yellow eyes or skin, light-colored stool, or brown urine.

Belviq initially raised concerns because it works somewhat like fenfluramine — which was withdrawn from the market because it damaged heart valves. However, there is no evidence that Belviq damages heart valves. Belviq may increase heart rate, so people taking it may need their heart rate checked.

Qsymia increases the risk of birth defects. Thus, the FDA required the manufacturer to have a risk evaluation and mitigation strategy (REMS). The REMS is intended to alert women to the risks and explain the need to avoid becoming pregnant while taking Qsymia. In addition, Qsymia is considered a controlled substance because one of its ingredients — phentermine — has the potential for abuse.

Factors to consider

If you meet the criteria for prescription weight-loss drugs, you and your doctor will need to evaluate the potential benefits against the possible risks of taking the medicine. Cost also is a consideration. Not all health insurance plans cover prescription weight-loss drugs.

As you consider weight-loss drugs, make sure that you make every effort to exercise, change your eating habits and adjust any other lifestyle factors that have contributed to your excess weight.

Weight-loss drugs aren't the easy answer to weight loss, but they can be a useful tool to help you make the necessary diet and lifestyle changes. Keeping off the pounds you've lost, however, is an ongoing concern. And many people, despite their efforts, still regain the weight.

Jun. 07, 2013 See more In-depth