Phentermine

Phentermine is the oldest still-in-use prescription weight-loss medication in the United States.³ It is a sympathomimetic amine — closely related to amphetamine in structure — that stimulates norepinephrine release in the hypothalamus, suppressing appetite. Generic, inexpensive, and reasonably effective for short-term use.¹

How it works

By increasing central norepinephrine activity, phentermine reduces hunger signals and increases satiety after smaller meals. Effect is most pronounced in the first 12 weeks of therapy; tolerance develops thereafter.¹

Who it is for

FDA-approved for adults with obesity (BMI ≥30, or ≥27 with weight-related comorbidity) as an adjunct to diet and exercise.³ Often used in 12-week courses, sometimes cycled, sometimes in combination with topiramate (Qsymia) for additive benefit.²

What to expect

Average weight loss of 3–7% over 12 weeks. Less effective than the GLP-1 class but markedly less expensive — useful where GLP-1s are inaccessible or where short-term jumpstart is the goal.

Cautions

• Stimulant side effects: insomnia, dry mouth, palpitations, mood changes, elevated blood pressure.
• Avoid in uncontrolled hypertension, hyperthyroidism, narrow-angle glaucoma, history of substance abuse, current MAOI use, pregnancy.
• Schedule IV controlled substance — DEA-tracked.
• Not a long-term solution. Plan for lifestyle reinforcement alongside the medication course.