Phentermine is a sympathomimetic amine, which is similar to an amphetamine. It is also known as an "anorectic" or "anorexigenic" drug. Phentermine stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.
Use caution when driving, operating machinery, or performing other hazardous activities. Phentermine may cause dizziness, blurred vision, or restlessness, and it may hide the symptoms of extreme tiredness. If you experience these effects, avoid hazardous activities.