Phentermine is a prescription medication used as a short-term adjunct to diet and exercise for weight loss in individuals who are obese or overweight with certain risk factors, such as high blood pressure, diabetes, or high cholesterol. It belongs to a class of drugs called sympathomimetic amines, which work by suppressing appetite and increasing energy expenditure.

Phentermine is thought to work by stimulating the release of certain neurotransmitters in the brain, such as dopamine, norepinephrine, and serotonin, which can help reduce hunger and increase feelings of fullness. It's typically used for a few weeks or months at a time, as its effectiveness may decrease over time and prolonged use can lead to tolerance.

While Phentermine can be effective for weight loss when used as part of a comprehensive weight management program, it's important to note that it's not a magic solution for obesity. It should only be used under the guidance of a healthcare professional and in conjunction with lifestyle changes such as healthy eating and regular physical activity.