Phentermine 37.5 mg (K25) is a prescription central nervous system stimulant used as a short-term aid in the management of obesity and weight reduction. It is typically prescribed for individuals who are overweight and have not been able to lose weight through diet and exercise alone. It is intended to be used only for a limited period as part of a comprehensive weight-loss program that includes lifestyle changes such as a reduced-calorie diet and regular physical activity. Phentermine works by stimulating the release of certain brain chemicals, such as norepinephrine, which help suppress appetite and increase feelings of fullness. This reduces hunger and helps patients consume fewer calories, supporting weight loss over time.

Because it is a stimulant, phentermine can increase heart rate, blood pressure, and energy levels. It should be taken exactly as prescribed, usually once daily in the morning to avoid sleep disturbances. It is not recommended for long-term use due to the risk of tolerance, dependence, and cardiovascular side effects.

Common side effects include dry mouth, insomnia, dizziness, restlessness, increased heart rate, and constipation. More serious risks may include elevated blood pressure, heart palpitations, mood changes, or anxiety, especially if misused or taken in high doses.