Phentermine Hydrochloride (HCL) is a prescription medication primarily used as a short-term aid in weight loss. It functions as an appetite suppressant, stimulating the central nervous system (similar to an amphetamine) to decrease hunger and increase energy expenditure. It is typically prescribed for individuals with a body mass index (BMI) ≥30, or ≥27 with comorbidities such as hypertension, diabetes, or high cholesterol. Phentermine is most effective when combined with diet, exercise, and behavior modification.