Phentermine is a prescription appetite suppressant approved by the FDA for short-term weight loss treatment. It works by stimulating the release of neurotransmitters that suppress appetite, making it easier to adhere to a calorie-restricted diet. Typically prescribed for individuals with a BMI of 30 or higher, or 27 with associated health conditions, phentermine is intended for short-term use, usually up to 12 weeks. Common side effects include dry mouth, insomnia, and increased heart rate. It's classified as a Schedule IV controlled substance due to its potential for abuse. Phentermine should only be used under the guidance of a healthcare professional.