phentermine, Adipex-P, Fastin (Discontinued), Obenix, Oby-Trim (Discontinued), Suprenza

Pharmacy Author:
Medical and Pharmacy Editor:
Medical and Pharmacy Editor:

GENERIC NAME: phentermine

BRAND NAMES: Adipex-P, Fastin (Discontinued), Obenix, Oby-Trim (Discontinued), Suprenza

DRUG CLASS AND MECHANISM: Phentermine is a drug that suppresses appetite. Its exact mechanism of action is unknown. It probably decreases appetite by acting on centers in the brain that control appetite. Phentermine is similar to amphetamine. It stimulates the nervous system, elevates blood pressure, and increases heart rate.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 30 and 37.5mg.; Orally disintegrating tablets: 15, 30, 37.5 mg.

STORAGE: Phentermine should be stored in a tight container at room temperature, 20 C to 25 C (68 F to 77 F).

PRESCRIBED FOR: Phentermine is combined with diet and exercise for the short-term treatment of obesity in individuals with a body mass index greater than or equal to 30 kg/m2 or greater than or equal to 27 kg/m2 with risk factors for heart disease. Phentermine should not be combined with other weight loss agents. The combination of phentermine and fenfluramine (FEN-PHEN) is associated with serious heart problems. Fenfluramine is no longer available in the United States.

DOSING: The recommended dose is 15-37.5 mg once daily. Adipex-P is administered about 1-2 hours after breakfast. The lowest effective dose should be used and evening doses should be avoided because phentermine causes insomnia.

DRUG INTERACTIONS: Phentermine is similar to amphetamine and may share some of the interactions associated with amphetamines. Combining phentermine with tricyclic antidepressants (for example, amitriptyline [Elavil, Endep]) or monoamine oxidase inhibitors [for example, phenelzine [Nardil], selegiline [Zelapar, Emsam, and Eldepryl], tranylcypromine [Parnate]) may result in high blood pressure and other serious reactions because of elevated serotonin levels in the blood. Phentermine should not be used within 14 days after stopping a monoamine oxidase inhibitor.

PREGNANCY: Use of phentermine during pregnancy has not been adequately evaluated.

NURSING MOTHERS: It is not known whether phentermine is excreted in human breast milk. Since other amphetamines are excreted in breast milk, phentermine should not be used while breastfeeding or, if used, nursing should be discontinued.

SIDE EFFECTS: Side effects of phentermine include nausea, vomiting, diarrhea, dry mouth, constipation, an unpleasant taste, hives, impotence, palpitations, high blood pressure, and fast heart rates (palpitations). Central nervous system side effects include hyperactivity, insomnia, restlessness, tremor, and dizziness. Phentermine, especially when combined with fenfluramine, has been associated with high pressures in the pulmonary arteries (pulmonary hypertension) and defects in heart valves, both serious complications. Physical and psychological dependence may occur with the long-term use of phentermine. A withdrawal reaction, which includes excessive drowsiness, fatigue, tremors and depression may occur after prolonged use.

Reference: FDA Prescribing Information


Medically Reviewed by a Doctor on 7/25/2014



Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Pill Finder Tool

Need help identifying pills and medications?
Use the pill identifier tool on RxList.


Back to Medications Index