Medically Reviewed on 11/16/2022

Generic Name: phendimetrazine

Brand Name: Bontril PDM

Drug Class: CNS Stimulants, Anorexiants; Stimulants; Sympathomimetic

What is phendimetrazine, and what is it used for?

Phendimetrazine is a medication used for short-term treatment of exogenous obesity as part of a weight loss regimen that includes caloric restriction, exercise and behavioral modification. Exogenous obesity results from overeating without sufficient activity levels, while endogenous obesity is caused by metabolic disorders. Obesity increases the risk for many diseases including cardiovascular disease and diabetes. Phendimetrazine may be used for a period of up to 12 weeks when a person is unable to lose weight with lifestyle measures alone.

Phendimetrazine is a sympathomimetic amine drug that mimics the action of natural chemicals in the body that stimulate the sympathetic nervous system. Phendimetrazine acts similarly to the stimulant class of drugs, the amphetamines. Phendimetrazine primarily works by suppressing appetite and increasing energy metabolism. Phendimetrazine also elevates blood pressure and has effects on the central nervous system (CNS), stimulating the release of chemical messengers (neurotransmitters) norepinephrine and dopamine.

As with the case of amphetamines, phendimetrazine also has a potential for misuse, abuse, dependence and addiction and must be used with caution. Diminishing drug effects (tachyphylaxis) and tolerance can develop with continued use of phendimetrazine like with other drugs of this class.


  • Do not use in patients with hypersensitivity to any of the components of phendimetrazine or to other sympathomimetic amines.
  • Do not use phendimetrazine in patients with any of the following conditions:
  • Phendimetrazine should be used with caution even in patients with mild hypertension.
  • Do not use phendimetrazine in pregnant or breastfeeding women.
  • Do not prescribe phendimetrazine to patients with a history of drug abuse.
  • The least amount feasible should be prescribed or dispensed at one time in order to minimize the possibility of misuse, abuse and overdosage.
  • Do not use concurrently or within 14 days of treatment with monoamine oxidase inhibitors (MAOIs), a class of antidepressants.
  • Do not use in combination with other appetite suppressants (anorectic agents), it can increase the risk for pulmonary hypertension. Monitor the patient for symptoms and discontinue the drug and evaluate patient if they develop symptoms.
  • Use of anorectic agents for longer than 3 months is associated with a 23-fold increase in the risk of developing pulmonary hypertension. Phendimetrazine should be discontinued immediately when tolerance to its anorectic effects develops, which usually occurs within a few weeks.
  • Do not prescribe phendimetrazine to individuals who have used any anorectic agents within the prior year.
  • Do not use in combination with other CNS stimulants, there is a potential risk for developing valvular heart disease or pulmonary hypertension.
  • Phendimetrazine can impair mental and physical abilities, caution patients to avoid potentially hazardous activities that require alertness.
  • Use with caution in patients with kidney function impairment.
  • Use with caution in elderly patients, and start at the lower end of the dosing range.


Weight loss occurs in the belly before anywhere else. See Answer

What are the side effects of phendimetrazine?

Common side effects of phendimetrazine include:

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

What are the dosages of phendimetrazine?

Capsules, extended-release: Schedule III

  • 105 mg

Tablet: Schedule III

  • 35 mg



  • Tablet: 35 mg every 8-12 hours 1 hour before meals
  • Range: 17.5 mg every 12 hours to 70 mg every 8 hours; not to exceed 70 mg orally every 8 hours
  • Extended-release capsule: 105 mg every morning


  • Because pediatric obesity is a chronic condition requiring long-term treatment, the use of amphetamines approved for short-term therapy is not recommended in patients under 17 years of age

Is phendimetrazine habit forming?


  • Phendimetrazine is related chemically and pharmacologically to the amphetamines, and has a potential for misuse, abuse, addiction, tolerance and dependence, which can result in overdose.
  • Dependence can lead to withdrawal symptoms such as fatigue, mental depression and sleep disturbances upon discontinuation of the drug.
  • Chronic intoxication with high doses can result in skin disorders, insomnia, hyperactivity, irritability, personality changes and psychosis.
  • Acute phendimetrazine overdose can cause confusion, restlessness, aggression, hallucination and panic states. Other overdose symptoms include nausea, vomiting, diarrhea, abdominal cramps, rapid heart rate, irregular heart rhythm, high or low blood pressure, and circulatory collapse. Severe overdose can result in convulsions, coma and death.
  • Overdose treatment is symptomatic and supportive, including:
    • Elimination of undigested drug with gastric lavage
    • Medications and intravenous fluids to stabilize blood pressure
    • Sedation with a barbiturate

What drugs interact with phendimetrazine?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

  • Severe interactions of phendimetrazine include:
  • Phendimetrazine has serious interactions with at least 30 different drugs.
  • Phendimetrazine has moderate interactions with at least 171 different drugs.
  • Mild interactions of phendimetrazine include:
    • desmopressin
    • eucalyptus
    • sage

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider about all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or healthcare provider if you have any questions about the medication.

Is phendimetrazine safe if pregnant or breastfeeding?

  • Infertility risk increases with obesity, and weight control before conception improves pregnancy outcomes. Medications for weight loss are not, however, recommended before pregnancy.
  • Weight loss during pregnancy may cause fetal harm. Do not use phendimetrazine in pregnant women.
  • It is not known if phendimetrazine is present in breast milk, however, other amphetamines are excreted in breast milk. Do not use in nursing mothers, discontinue the drug or nursing, depending on the importance of the drug to the mother.

What else should I know about phendimetrazine?

  • Take phendimetrazine exactly as prescribed. Do not take higher or more frequent doses.
  • Phendimetrazine has a potential for addiction, use with extreme caution.
  • Phendimetrazine is only used for a short-term (12 weeks) as an adjunct and it is important to follow appropriate calorie restrictions, exercises and a healthy lifestyle.
  • Phendimetrazine can impair physical and mental abilities required to perform hazardous tasks such as driving and operating heavy machinery, avoid engaging in such activities while on treatment.
  • Store phendimetrazine safely out of reach of children.
  • In case of overdose, seek immediate medical help or contact Poison Control.

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Phendimetrazine is a medication used for short-term treatment of exogenous obesity as part of a weight loss regimen that includes caloric restriction, exercise, and behavioral modification. Do not use phendimetrazine in pregnant or breastfeeding women. Common side effects of phendimetrazine include high blood pressure in the lungs (primary pulmonary hypertension), regurgitant cardiac valvular disease, palpitations, rapid heart rate (tachycardia), reduced blood flow to any of the organs (ischemic events), weakening and thinning of heart muscle (dilated cardiomyopathy), hypertension, flushing, excessive sweating (diaphoresis), dry mouth (xerostomia), nausea, stomach pain, constipation, diarrhea, urinary frequency, painful urination (dysuria), and others.

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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.

Medically Reviewed on 11/16/2022