Phentermine is used to speed weight loss in overweight people. It is used together with diet and exercise to treat obesity, especially in individuals with risk factors such as high blood pressure, high cholesterol, or diabetes.

Phentermine operates similarly to an amphetamine. It stimulates the central nervous system (nerves and brain), leading to an increase in heart rate and blood pressure while reducing appetite. This medication belongs to a class of medications called anorectics, and it works by suppressing appetite.