Phentermine is a prescription weight-loss medication classified as a sympathomimetic amine (similar to an amphetamine). It is used as a short-term appetite suppressant in combination with diet, exercise, and behavioral changes to treat obesity, particularly in individuals with risk factors such as high blood pressure, high cholesterol, or diabetes.

Phentermine works by stimulating the central nervous system (nerves and brain), which increases heart rate and blood pressure and decreases appetite.