What drugs are approved for weight loss?

Four weight-loss drugs have been approved by the U.S. Food and Drug Administration for long-term use:

• Bupropion-naltrexone (Contrave)
• Liraglutide (Saxenda)
• Orlistat (Xenical)
• Phentermine-topiramate (Qsymia)

Most prescription weight-loss drugs work by decreasing appetite or increasing feelings of fullness. Some do both. The exception is orlistat. It works by interfering with absorption of fat.

Bupropion-naltrexone

Bupropion-naltrexone is a combination drug. Naltrexone is used to treat alcohol and opioid dependence. Bupropion is an antidepressant and quit-smoking aid. Like all antidepressants, bupropion carries a warning about suicide risk. Bupropion-naltrexone can raise blood pressure, and monitoring is necessary at the start of treatment. Common side effects include nausea, headache and constipation.

Liraglutide

Liraglutide is also used to manage diabetes. Unlike other weight-loss drugs, liraglutide is given by injection. Nausea is a common complaint. Vomiting may limit its use.

Orlistat

Orlistat is also available in a reduced-strength form without a prescription (Alli). Orlistat can cause bothersome gastrointestinal side effects, such as flatulence and loose stools. You need to follow a low-fat diet when taking this medicine. Rare cases of serious liver injury have been reported with orlistat. However, no cause-and-effect relationship has been established.

Phentermine-topiramate

Phentermine-topiramate is a combination of a weight-loss drug (phentermine) and an anticonvulsant (topiramate). Phentermine has the potential to be abused because it acts like an amphetamine. Other possible side effects include an increase in heart rate and blood pressure, insomnia, constipation, and nervousness. Topiramate increases the risk of birth defects.

Phentermine by itself (Adipex-P, Lomaira) is also used for weight loss. It's one of four similar weight-loss drugs approved for short-term use (less than 12 weeks). The other drugs in this group aren't widely prescribed.