Phentermine, also sold under the brand name Adipex, is a prescription medication that helps people lose weight. It works by suppressing appetite and boosting energy levels, making it easier to stick to a healthy diet and exercise routine. This guide will explain how Phentermine works, its benefits, potential side effects, and important safety information. What Is Phentermine (Adipex)? Phentermine is an appetite suppressant used for short-term weight loss. It belongs to a class of drugs called sympathomimetic amines, which affect chemicals in the brain that control hunger. By reducing appetite and increasing energy, Phentermine helps users eat less and stay active, which is key for weight loss. Phentermine is prescribed as part of a weight loss plan that includes a healthy diet and regular exercise. It is not meant for long-term use, but it can be a useful tool for jumpstarting weight loss when combined with lifestyle changes.