Medically Reviewed on 3/30/2023

Generic Name: phentermine

Brand Name: Adipex-P, Lomaira

Discontinued Brands: Fastin, Oby-Trim, Obestin-30, OnaMast, Tora, Obenix, Suprenza, Wilpo

What is phentermine, and what is it used for?

Phentermine is a drug that suppresses appetite.

  • 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.

What are the side effects of phentermine?

Side effects of phentermine include:

Central nervous system side effects include:

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.

What is the dosage for phentermine?

  • 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.

Which drugs interact with phentermine?


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Pregnancy and breastfeeding

  • Use of phentermine during pregnancy has not been adequately evaluated.
  • 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.

What else should I know about phentermine?

What preparations of phentermine are available?
  • Tablets: 8 and 37.5 mg.
  • Capsules: 15, 30, 37.5 mg.
How should I keep phentermine stored?

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

How does phentermine work?
  • The exact mechanism of action of phentermine 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.


Phentermine is a drug that suppresses the appetite for weight loss. Phentermine should be combined with exercise and diet for the short term treatment of obesity. Drug interactions may occur with some tricyclic antidepressants or monoamine oxidase inhibitors. Side effects include palpitations, high blood pressure, hives, impotence, constipation, dry mouth, diarrhea, vomiting, and nausea.

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See more info: phentermine on RxList
Medically Reviewed on 3/30/2023
Medically reviewed by John P. Cunha, DO, FACOEP; Board Certified Emergency Medicine


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