Dec 16, - Phentermine (Adipex-P) is used for weight loss. It decreases the appetite and stimulates the body to burn calories more quickly. Find patient medical information for Adipex-P Oral on WebMD including its uses, side effects and safety, interactions, pictures, warnings and user ratings. I started using Phentermine in to help me lose weight. I had heard about it. I went to my doctor and she prescribed it. She said it was safe.