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Phendimetrazine is used for weight loss. The most common side effects are related to its mild stimulant effects (increased blood pressure or heart rate, tremors, trouble sleeping). Phendimetrazine is a controlled substance because it can be misused or lead to dependence. Store phendimetrazine in a safe place to protect it from theft. It is illegal to sell or give away this medicine.

Uses

What is phendimetrazine used for?

Phendimetrazine is commonly used to help people with obesity or people who are overweight lose weight. 

Phendimetrazine may also be used for other conditions as determined by your health care provider.

How does phendimetrazine work (mechanism of action)?

Phendimetrazine is thought to help people lose weight by reducing appetite, which may help you want to eat less food.

How is phendimetrazine supplied (dosage forms)?

Brands and other names

  • Bontril PDM
  • Melfiat
  • Plegine

Dosage forms and strengths

  • 105 mg extended-release oral capsules
  • 35 mg oral tablets

How should I store phendimetrazine?

Phendimetrazine should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from moisture. 

Side Effects

What are the most common side effects of phendimetrazine?

The most common side effects of phendimetrazine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Feeling of skipped heartbeats
  • Fast heartbeat
  • High blood pressure
  • Feeling restless
  • Dizziness
  • Trouble sleeping 
  • Tremors
  • Sweating more than usual
  • Headache
  • Dry mouth
  • Nausea
  • Diarrhea
  • Increased urination

There may be other side effects of phendimetrazine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of phendimetrazine?

While less common, the most serious side effects of phendimetrazine are described below, along with what to do if they happen.

Pulmonary Hypertension. Phendimetrazine may increase your risk of developing pulmonary hypertension (high blood pressure in the blood vessels between your heart and your lungs), which can be life-threatening. The risk may be higher in those taking the medicine for longer periods. Stop taking phendimetrazine and get help right away If you have any of the following symptoms.

  • Trouble breathing
  • Chest pain
  • Fainting 
  • Swelling in your legs

Heart Valve Problems. Phendimetrazine or medicines like it may rarely cause problems with your heart valves, which can be serious. Stop taking phendimetrazine and get help right away if you have any of the following symptoms.

  • Unusual shortness of breath
  • Feeling of skipped heartbeats
  • Chest pain
  • Swelling in the legs
  • Fainting or feeling dizzy

Severe Allergic Reactions. Phendimetrazine may cause allergic reactions, which can be serious. Stop taking phendimetrazine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use phendimetrazine?

Allergies to Ingredients. People who are allergic to any of the following should not take phendimetrazine.

  • Bontril PDM
  • Melfiat
  • Plegine
  • Phendimetrazine
  • Any other medicine known as a sympathomimetic 
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific phendimetrazine products they stock.

Heart Disease. Phendimetrazine should not be used by those with a history of heart attack, stroke, or heart failure.

High Blood Pressure. Phendimetrazine should not be used by those with uncontrolled high blood pressure. 

Pulmonary Hypertension. Phendimetrazine should not be used by those with pulmonary hypertension.

Thyroid Problems. Phendimetrazine should not be used by those with an overactive thyroid, also known as hyperthyroidism. 

Agitation. Phendimetrazine is not for people who feel restless, uneasy, nervous, or cranky. These feelings can be caused by stress and certain medical problems.

Substance Use Disorder. Phendimetrazine should not be used by those with a history of substance use disorder.

Eye Problems. Phendimetrazine should not be used by those with glaucoma. 

Pregnancy. Do not take phendimetrazine if you are pregnant. If you become pregnant, contact your health care provider right away. See the Pregnancy section for more details. 

Breastfeeding. Do not take phendimetrazine if you are breastfeeding. You must stop either breastfeeding or phendimetrazine. See the Breastfeeding section for more details.

Drug Interactions. Phendimetrazine should not be taken while you are using certain other medicines. Before taking phendimetrazine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details. 

What should I know about phendimetrazine before using it?

Do not take phendimetrazine unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share phendimetrazine with other people, even if they have the same condition as you. It may harm them.

Keep phendimetrazine out of the reach of children. Phendimetrazine is a controlled substance because it can be misused or lead to dependence. Store phendimetrazine in a safe place to protect it from theft. It is illegal to sell or give away this medicine.

Phendimetrazine can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how phendimetrazine affects you.

Phendimetrazine is usually only taken for a few weeks. This medicine may be habit-forming and has a risk of being misused. Do not increase your dose, take it more often, or use it for a longer time than prescribed. 

What should I tell my health care provider before using phendimetrazine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if phendimetrazine is right for you.

In particular, make sure that you discuss any of the following.

Other Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Heart disease, heart murmur, or heart valve problems
  • Abnormal heart rate or rhythm
  • High blood pressure, including pulmonary hypertension
  • Glaucoma
  • Thyroid problems
  • Diabetes
  • Mental health problems, including substance use disorder
  • Use of another weight loss medicine or supplement within the last year
  • Kidney problems

Pregnancy. Do not take phendimetrazine if you are pregnant. Weight loss is not recommended during pregnancy, even if you are already overweight. If you become pregnant while taking phendimetrazine, contact your health care provider right away.

Breastfeeding. Do not take phendimetrazine if you are breastfeeding. Tell your health care provider if you are breastfeeding or plan to breastfeed. It is not known if phendimetrazine passes into breast milk. Your health care provider will advise you if you should stop breastfeeding or stop phendimetrazine.

Interactions

Does phendimetrazine interact with foods or drinks?

The immediate-release tablet should be taken one hour before meals. 

The extended-release capsule should be taken 30 minutes to one hour before the morning meal.

The risk of dizziness may be increased if you drink alcohol while taking phendimetrazine. 

Does phendimetrazine interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking phendimetrazine.

  • Linezolid (Zyvox), which is a medicine used for certain bacterial infections
  • A monoamine oxidase inhibitor (MAOI) within the past two weeks, which is a medicine usually used for depression or Parkinson’s disease
  • A medicine or supplement for weight loss
  • A medicine for high blood pressure
  • A medicine for diabetes

This may not be a complete list of medicines that can interact with phendimetrazine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much phendimetrazine?

If you or someone else has used too much phendimetrazine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of phendimetrazine?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.