Phentermine is used along with a doctor-approved, reduced-calorie diet, exercise, and behavior change program to help you lose weight. It is used in people who are significantly overweight (obese) and have not been able to lose enough weight with diet and exercise alone. Losing weight and keeping it off can reduce the many health risks that come with obesity, including heart disease, diabetes, high blood pressure, and a shorter life.
It is not known how this medication helps people to lose weight. It may work by decreasing your appetite, increasing the amount of energy used by your body, or by affecting certain parts of the brain. This medication is an appetite suppressant and belongs to a class of drugs called sympathomimetic amines.