Phentermine and topiramate are different medications that can affect weight through different mechanisms. They may be prescribed separately in selected situations, and they are also available together in an FDA-approved extended-release product, Qsymia.
Phentermine is a sympathomimetic appetite suppressant. It can reduce hunger but may increase heart rate or blood pressure and can cause insomnia, anxiety or dry mouth in some patients.
Topiramate is approved for epilepsy and migraine prevention and may reduce appetite or food cravings. When used alone for weight management, that use is off-label.
The extended-release combination is FDA approved for chronic weight management in eligible patients when used with reduced-calorie nutrition and increased physical activity.
There is no universal answer. The choice depends on cardiovascular history, migraine history, kidney-stone risk, pregnancy potential, psychiatric symptoms, medication interactions and prior response.
Weight, blood pressure, heart rate, side effects and treatment response should be reviewed regularly. Pregnancy precautions are especially important for topiramate-containing treatment.
Learn more about medical weight-loss medications.
