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Phentermine Hydrochloride

Pronunciation: FEN-ter-meen
Class: Anorexiant

Trade Names

- Tablets, oral 37.5 mg
- Capsules, oral 37.5 mg

Phentermine Hydrochloride
- Tablets, oral 37.5 mg
- Capsules, oral 15 mg
- Capsules, oral 30 mg
- Capsules, oral 37.5 mg

- Tablets, disintegrating, oral 15 mg
- Tablets, disintegrating, oral 30 mg


Modulates central norepinephrine and dopamine receptors through promotion of catecholamine release.



Orally disintegrating tablet

T max is 3 to 4.4 h. Administration after a high-fat/high-calorie breakfast decreased the C max by approximately 5% and the AUC by approximately 12%.

Special Populations

Renal Function Impairment

Exposure increases can be expected.

Indications and Usage

Short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification, and caloric restriction in the management of exogenous obesity for patients with an initial BMI 30 kg/m 2 or more, or 27 kg/m 2 or more in the presence of other risk factors (eg, hypertension, diabetes, hyperlipidemia).


Hypersensitivity or idiosyncrasy to sympathomimetic amines; advanced arteriosclerosis; CV disease (eg, coronary artery disease, stroke, arrhythmias, CHF, moderate to severe or uncontrolled hypertension); hyperthyroidism; glaucoma; agitated states; history of drug abuse; during or within 14 days following the administration of an MAOI; pregnancy and lactation (orally disintegrating tablets only).

Dosage and Administration

Adults and adolescents 17 y and older Adipex-P capsules/tablets and phentermine tablets

PO 1 capsule or tablet daily, administered before breakfast or 1 to 2 h after breakfast. For some patients, ½ tablet (18.75 mg) daily may be adequate, while in some cases, it may be desirable to give ½ tablet (18.75 mg) 2 times a day.

Phentermine capsules

PO 15 to 30 mg approximately 2 h after breakfast.

Orally disintegrating tablets

PO 1 tablet in the morning with or without food.

General Advice

  • Administer capsules 2 h after breakfast. Administer Adipex-P capsules and tablets either before breakfast or 1 to 2 h after breakfast. Orally disintegrating tablets may be administered in the morning with or without food.
  • Late evening medication should be avoided because of the possibility of resulting insomnia.
  • Immediately place the orally disintegrating tablet on top of the tongue where it will dissolve; then swallow it with or without water.


Store at 68° to 77°F. Protect capsules from moisture and light.

Drug Interactions

Adrenergic neuron blockers (eg, reserpine)

The hypotensive effect of adrenergic blockers may be reduced. Monitor BP.


Concomitant use of alcohol may enhance the adverse reactions of phentermine.

Furazolidone, MAOIs (eg, phenelzine)

May cause hypertensive crisis and intracranial hemorrhage. Avoid coadministration of furazolidone and phentermine. Coadministration of MAOIs and phentermine is contraindicated.

Insulin, oral hypoglycemic agents (eg, sulfonylureas [eg, tolbutamide])

Requirements of these agents may be altered, necessitating a reduction in the dose of the oral hypoglycemic agent or insulin.


Phentermine may reduce retention and diagnostic efficacy of iobenguane. False-negative iobenguane imaging tests may result. Discontinue phentermine at least 72 h prior to iobenguane administration.

SSRIs (eg, fluoxetine)

Sympathomimetic effects of phentermine and risk of serotonin syndrome may be increased. Coadministration is not recommended.

Weight-loss products (eg, herbal, OTC, or prescription products)

Safety and efficacy of concurrent use with phentermine have not been established. Coadministration is not recommended.

Adverse Reactions


Hypertension; ischemic events; palpitation; primary pulmonary hypertension; regurgitant cardiac valvular disease; tachycardia.


Dizziness; dysphoria; headache; euphoria; insomnia; overstimulation; psychotic episodes; restlessness; tremor.




Constipation; diarrhea; dry mouth; GI disturbances; unpleasant taste.


Changes in libido; impotence.



Category X (orally disintegrating tablets only); Category C . Contraindicated in pregnancy (orally disintegrating tablets); may cause fetal harm.


Undetermined. Contraindicated in lactation (orally disintegrating tablets).


Safety and efficacy not established in pediatric patients 16 y or younger.


Use with caution.

Renal Function

Use with caution.

Hazardous Tasks

May impair the ability of patients to engage in potentially hazardous activities, such as operating machinery or driving a motor vehicle.

Drug dependence

Psychological and physical dependence may occur with continued use; this class of drugs has been extensively abused.


Use with caution in patients with even mild hypertension.


Insulin requirements in patients with diabetes mellitus may be altered in association with the use of phentermine and the concomitant dietary regimen.


Tolerance to the anorectic effect usually develops within a few weeks.

Primary pulmonary hypertension

Has been reported with phentermine alone and in combination with fenfluramine or dexfenfluramine.

Valvular heart disease

Serious regurgitant cardiac valvular disease has been reported with concurrent use of phentermine and fenfluramine or dexfenfluramine.



Abdominal cramps, arrhythmias, assaultiveness, circulatory collapse, coma, confusion, convulsions, death, depression, diarrhea, fatigue, hallucinations, hyperreflexia, hypertension, hypotension, nausea, panic states, rapid respiration, restlessness, tremor, vomiting.

Patient Information

  • Encourage patients to follow a medically supervised weight-reduction program. Emphasize that this medication will only work in conjunction with a caloric-restricted diet and exercise program.
  • Explain that appetite-suppressant effects are temporary and tolerance to medication and dependence can occur. Caution patients not to increase the dose in an effort to overcome the tolerance when it occurs.
  • Advise pregnant women and breast-feeding mothers not to use phentermine.
  • Caution patients that this drug may impair the ability to drive or perform other tasks requiring mental alertness.
  • Advise patients to notify their health care provider immediately if the following symptoms occur: decreased exercise tolerance, dyspnea, swelling of the feet or ankles, fainting, chest pain, palpitations, nervousness, or dizziness.
  • Inform patients about the risks of phentermine use, the symptoms of potential adverse reactions, and when to contact a health care provider and/or take other action. The risks include but are not limited to development of primary pulmonary hypertension, development of serious valvular heart disease, an increase in BP, and possible drug interactions.

Copyright © 2009 Wolters Kluwer Health.