Phentermine is a prescription medication used primarily as an appetite suppressant to aid in weight loss. It belongs to a class of drugs known as sympathomimetic amines, which work by stimulating the release of certain neurotransmitters in the brain that help reduce hunger. Phentermine is typically prescribed as part of a comprehensive weight-loss plan that includes diet, exercise, and behavioral changes, and is intended for short-term use, usually a few weeks.