Phentermine

What it means

Phentermine is a stimulant related to amphetamine. It reduces appetite through brain chemicals such as norepinephrine. It is one of the oldest and least expensive weight-loss medicines in the US.

Its label approves it only for short-term use, a few weeks, alongside diet and exercise in adults with obesity or overweight with risk factors. Some clinicians prescribe it longer; that is a clinical judgment outside the label. It is a Schedule IV controlled substance, so prescriptions have extra rules.

Common side effects include a faster heart rate, higher blood pressure, trouble sleeping, dry mouth and restlessness. The label says not to use it with heart disease, uncontrolled high blood pressure, an overactive thyroid, glaucoma, a history of drug misuse, during pregnancy or within 14 days of an MAO inhibitor.

Phentermine is also one half of Qsymia, a long-term combination medicine.

Why it matters

Phentermine is a common low-cost option, but its short-term label and heart effects make it a different choice from GLP-1 medicines.