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Phendimetrazine (Monograph)

Brand name: Bontril
Drug class: Amphetamine Derivatives
VA class: GA751
CAS number: 50-58-8

Medically reviewed by on Nov 10, 2023. Written by ASHP.


Amphetamine congener; anorexigenic agent.

Uses for Phendimetrazine

Exogenous Obesity

Adjunct to caloric restriction in the short-term management (a few weeks) of exogenous obesity.

Use only for short-term monotherapy; not for use in combination with any other drug for weight loss.

Phendimetrazine Dosage and Administration


  • Teach patient to curtail overeating and consume a suitable diet to help induce and maintain weight loss.


Oral Administration

Administer conventional tablets orally 2 or 3 times daily, 1 hour before meals.

Administer extended-release capsules orally once daily, 30–60 minutes before the morning meal.


Available as phendimetrazine tartrate; dosage expressed in terms of the salt.

Pediatric Patients

Exogenous Obesity
Conventional Tablets

Children ≥12 years of age: 35 mg 2 or 3 times daily, given 1 hour before meals. A dosage of 17.5 mg 2 or 3 times daily may be adequate for some patients.

Extended-release Capsules

Children ≥12 years of age: 105 mg once daily, given 30–60 minutes before the morning meal.


Exogenous Obesity
Conventional Tablets

35 mg 2 or 3 times daily, given 1 hour before meals. A dosage of 17.5 mg 2 or 3 times daily may be adequate for some patients.

Extended-release Capsules

105 mg once daily, given 30–60 minutes before the morning meal.

Prescribing Limits

Pediatric Patients

Exogenous Obesity

Children ≥12 years of age: Maximum 70 mg 3 times daily (as conventional tablets).

Children ≥12 years of age: Maximum 105 mg once daily (as extended-release capsules).


Exogenous Obesity

Maximum 70 mg 3 times daily (as conventional tablets).

Maximum 105 mg once daily (as extended-release capsules).

Cautions for Phendimetrazine


  • Symptomatic cardiovascular disease, hyperthyroidism, moderate to severe hypertension, pulmonary hypertension, glaucoma, or advanced arteriosclerosis.

  • Highly nervous or agitated state or history of drug abuse.

  • Concurrent therapy with other CNS stimulants or anorexigenic drugs.

  • Within 14 days of MAO inhibitor therapy.

  • Known hypersensitivity or idiosyncrasy to sympathomimetic amines.



Primary Pulmonary Hypertension

Risk of primary pulmonary hypertension (frequently fatal), particularly when used in combination with at least one other anorexigenic agent, or in those with a history of receiving at least one other anorexigenic agent. Risk increased by 23-fold when anorexigenic agents are used for >3 months. Increased risk following repeated courses of phendimetrazine cannot be ruled out.

Discontinue immediately if new-onset or exacerbation of exertional dyspnea or unexplained symptoms of angina, syncope, or edema of the lower extremities occur, and evaluate for possible pulmonary hypertension.

Valvular Heart Disease

Valvular heart disease reported following use of some anorexigenic agents (e.g., fenfluramine, dexfenfluramine [both no longer commercially available in the US]), particularly when used for extended periods of time, at higher than recommended dosages, and/or in combination with other anorexigenic agents.

Abnormal heart valve findings have been reported in some patients receiving phendimetrazine. Weigh potential risks against benefits of therapy.

Consider performing baseline cardiac evaluation to detect preexisting valvular heart diseases prior to initiation of therapy. Use not recommended in patients with known heart murmur or valvular heart disease. Echocardiogram during and after treatment may be useful for detecting any valvular disorders that may occur.

To limit unwarranted exposure and risks, continue therapy only if patient has achieved satisfactory weight loss (e.g., ≥4 pounds [1.8 kg], or as determined by physician and patient) within first 4 weeks of therapy.

Tolerance to Anorexigenic Effect

Tolerance to anorexigenic effect usually develops within a few weeks. When it does, discontinue therapy; do not attempt to increase effect by exceeding recommended dosage.

CNS Effects

Performance of activities requiring mental alertness or physical coordination may be impaired. (See Advice to Patients.)

Abuse Potential

Potential for abuse; habituation or addiction reported with phendimetrazine and similar drugs (e.g., amphetamines).

Manifestations of chronic intoxication may include psychosis resembling schizophrenia, severe dermatoses, marked insomnia, irritability, hyperactivity, and personality changes.

Abrupt discontinuance following prolonged high dosage may result in extreme fatigue, depression, and sleep EEG changes.

Sensitivity Reactions

Tartrazine Sensitivity

Some preparations (e.g., 35-mg conventional tablets manufactured by Sandoz) contain tartrazine (FD&C yellow No. 5), which may cause allergic reactions including bronchial asthma in susceptible individuals. Incidence of tartrazine sensitivity is low, but it frequently occurs in patients who are sensitive to aspirin.

General Precautions

Prescribe and dispense in the smallest feasible quantity to minimize possibility of overdosage.


Use with caution in patients with mild hypertension; monitor BP closely. Contraindicated in those with moderate or severe hypertension.

Diabetes Mellitus

Use with caution in patients with diabetes mellitus; insulin requirements may decrease in association with phendimetrazine use and the concomitant dietary regimen and weight loss.

Specific Populations


Category C.

Whether potential benefits of anorexigenic agents outweigh risks is questionable; use of these agents during pregnancy (especially during the first trimester) probably should be considered a contraindication.


Not known whether phendimetrazine is distributed into milk; however, because of its low molecular weight, the drug is expected to distribute into milk. Caution if used in nursing women.

Pediatric Use

Use not recommended in children <12 years of age.

Common Adverse Effects

Palpitation, tachycardia, increased BP, overstimulation, restlessness, dizziness, insomnia, agitation, flushing, tremor, sweating, headache, psychosis, blurred vision, dry mouth, diarrhea, constipation, nausea, stomach pain, changes in libido, urinary frequency, dysuria.

Interactions for Phendimetrazine

Specific Drugs




Anorexigenic agents

Risk of serious cardiac problems

Avoid concomitant use (including with OTC drugs or herbal preparations) (see Contraindications under Cautions); phendimetrazine not recommended for patients who used any anorexigenic agents within prior year

CNS stimulants

Concomitant use contraindicated

Guanethidine (no longer commercially available in the US)

Decreased hypotensive effect


Possible decrease in insulin requirements in patients with diabetes mellitus

Use concomitantly with caution

MAO inhibitors

Potential for hypertensive crisis

Phendimetrazine use during or within 14 days of MAO inhibitor use is contraindicated

Phendimetrazine Pharmacokinetics



Readily absorbed from the GI tract following oral administration.


Effects persist for about 4 hours.

Extended-release capsules produce prolonged therapeutic effect. Effects achieved with one 105-mg extended-release capsule are similar to those achieved with three 35-mg conventional tablets administered at 4-hour intervals.



Not known whether phendimetrazine is distributed into milk; however, because of its low molecular weight, the drug is expected to distribute into milk.



Undergoes limited biotransformation.

Elimination Route

Excreted principally in urine.


Conventional tablets: Approximately 1.9–3.7 hours.

Extended-release capsules: Approximately 3.7–9.8 hours.




Conventional Tablets and Extended-release Capsules

Tight, light-resistant containers at 20–25°C. Protect from moisture.


  • Produces anorexigenic effect and loss of weight.

  • Like other amphetamine derivatives, has no primary effect on appetite; anorexigenic action probably is secondary to CNS stimulation.

Advice to Patients

  • Potential for drug to impair mental alertness or physical coordination; caution when driving or operating machinery until effects on individual are known.

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as any concomitant illnesses (e.g., glaucoma, high BP, cardiac disease).

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.

  • Importance of informing patients of other important precautionary information. (See Cautions.)


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

Subject to control under the Federal Controlled Substances Act of 1970 as a schedule III (C-III) drug.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

Phendimetrazine Tartrate


Dosage Forms


Brand Names



Capsules, extended-release

105 mg*

Bontril Slow Release (C-III)


Phendimetrazine Tartrate Extended-release Capsules (C-III; with povidone)



35 mg*

Bontril PDM (C-III; with isopropyl alcohol and povidone; scored)


Phendimetrazine Tartrate Tablets (C-III; with povidone)

RLC, Sandoz

AHFS DI Essentials™. © Copyright 2023, Selected Revisions November 20, 2012. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

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