Generic name: phendimetrazine [ fen-di-MEH-tra-zeen ]
Brand names: Bontril, Melfiat
Drug classes: Anorexiants, CNS stimulants

Medically reviewed by Sophia Entringer, PharmD. Last updated on Apr 9, 2024.

What is phendimetrazine?

Phendimetrazine is a sympathomimetic amine, which is similar to an amphetamine.

Phendimetrazine stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.

Phendimetrazine is a prescription medicine that is used together with diet and exercise to treat obesity.

Warnings

You should not use phendimetrazine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse.

Do not use this medicine if you have used an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine. A dangerous drug interaction could occur, leading to serious side effects.

Weight loss during pregnancy can harm an unborn baby, even if you are overweight. Do not use phendimetrazine if you are pregnant or breast feeding.

Do not stop using this medicine suddenly after long-term use, or you could have unpleasant withdrawal symptoms. Ask your doctor how to avoid withdrawal symptoms when you stop using this medicine . Do not crush, chew, break, or open the extended-release capsule. Swallow it whole. Breaking or opening the pill may cause too much of the drug to be released at one time.

Before taking this medicine

You should not use phendimetrazine if you are allergic to it, or if you have:

• severe heart problems;

• advanced coronary artery disease (clogged arteries);

• severe or uncontrolled high blood pressure;

• overactive thyroid;

• glaucoma;

• extreme agitation or nervousness; or

• a history of drug abuse.

Do not use phendimetrazine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.

Weight loss during pregnancy can harm an unborn baby, even if you are overweight. Do not use phendimetrazine if you are pregnant or breast feeding. Tell your doctor right away if you become pregnant during treatment.

Tell your doctor if you have ever had:

• heart disease or coronary artery disease;

• high blood pressure;

• diabetes (your diabetes medication dose may need to be adjusted); or

• an allergy to food dye or aspirin.

Phendimetrazine is not approved for use by anyone younger than 17 years old.

How should I take phendimetrazine?

Take phendimetrazine exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

This medicine is usually taken 30 minutes to 1 hour before meals. Follow your doctor's dosing instructions very carefully.

Never use phendimetrazine in larger amounts, or for longer than prescribed. Taking more of this medication will not make it more effective and can cause serious, life-threatening side effects.

Phendimetrazine is for short-term use only. The effects of appetite suppression may wear off after a few weeks.

Phendimetrazine may be habit-forming. Misuse can cause addiction, overdose, or death. Selling or giving away this medicine is against the law.

Call your doctor at once if you think this medicine is not working as well, or if you have not lost at least 4 pounds within 4 weeks.

Do not stop taking this medicine suddenly, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using this medicine.

Store at room temperature away from moisture and heat. Keep the bottle tightly closed when not in use.

Dosing information

Usual Adult Dose for Obesity:

Extended-release:
-105 mg orally once a day, 30 to 60 minutes before morning meal

Immediate-release:
-35 mg orally 2 or 3 times a day, one hour before meals
-Maximum dose: 70 mg orally 3 times a day, one hour before meals

Comments:
-For use as monotherapy only.
-Extended-release: The active drug in each extended release capsule approximates the action of three 35 mg immediate-release doses taken at 4 hour intervals.
-Immediate-release: Dosage should be individualized to obtain an adequate response with the lowest effective dose; 17.5 mg per dose may be adequate in some cases.

Use: Management of exogenous obesity as a short-term adjunct in a regimen of weight reduction based on caloric restriction in patients with
-an initial BMI of 30 kg/m2 or greater OR
-an initial BMI of 27 kg/m2 or greater in the presence of other risk factors (e.g., hypertension, diabetes, hyperlipidemia) who have not responded to appropriate weight reducing regimen (diet and/or exercise) alone.

Related/similar drugs

Mounjaro, Zepbound, Wegovy, semaglutide, phentermine, Saxenda, Alli

What happens if I miss a dose?

Use the medicine as soon as you can, but skip the missed dose if it is late in the day. Do not use two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phendimetrazine can be fatal.

Overdose symptoms may include confusion, panic, hallucinations, extreme restlessness, nausea, vomiting, diarrhea, stomach cramps, feeling tired or depressed, irregular heartbeats, weak pulse, seizure, or slow breathing (breathing may stop).

What to avoid

Avoid driving or hazardous activity until you know how phendimetrazine will affect you. Your reactions could be impaired.

Drinking alcohol with this medicine can cause side effects.

Phendimetrazine side effects

Get emergency medical help if you have signs of an allergic reaction to phendimetrazine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

• pounding heartbeats or fluttering in your chest;

• tremors, severe agitation, feeling restless, trouble sleeping;

• unusual changes in mood or behavior;

• little or no urination; or

• increased blood pressure - severe headache, blurred vision, pounding in your neck or ears, anxiety, nosebleed.

Common phendimetrazine side effects may include:

• flushing (warmth, redness, or tingly feeling);

• increased sweating or urination;

• dizziness, headache;

• blurred vision;

• dry mouth, nausea;

• diarrhea, constipation, stomach pain; or

• increased or decreased interest in sex.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect phendimetrazine?

Other drugs may affect phendimetrazine, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use phendimetrazine only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer

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