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Micromedex DrugNotes [Internet].

Fenfluramine (By mouth)

Fenfluramine (fen-FLUR-a-meen)

Published: May 1, 2015.

Used for short periods of time as part of a diet plan to help you lose weight.

When This Medicine Should Not Be Used

You should not use this medicine if you have had an allergic reaction to fenfluramine or related medicines such as amphetamines, asthma medicine (metaproterenol, terbutaline, or isoproterenol), or certain cold and allergy medicine (decongestants such as ephedrine, pseudoephedrine, or phenylpropanolamine). You should not use this medicine if you have problems with drug or alcohol abuse, heart disease, or glaucoma. You should not use fenfluramine if you have taken a type of medicine called a MAO inhibitor (such as Nardil®, Marplan®, or Parnate®) within the past 14 days. These 2 medicines taken together or within 14 days of each other can cause dangerously high blood pressure.

How to Use This Medicine


  • Your doctor will tell you how much to take and how often.
  • Take 1 hour before meals.

If a dose is missed:

  • If you do not remember that you missed a dose until after you have eaten, skip the missed dose. Take your next dose at the regular time.
  • You should not use two doses at the same time.

How to Store and Dispose of This Medicine:

  • Store at room temperature, away from heat, moisture, and direct light.
  • Keep all medicine out of the reach of children.

Drugs and Foods to Avoid

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Avoid drinking alcohol while taking this medicine.
  • Make sure your doctor knows if you are also taking blood pressure medicine, medicine to treat depression, or any medicine that may make you sleepy, such as sleeping pills, tranquilizers, some cold or allergy medicines, or strong pain killers.

Warnings While Using This Medicine

  • Check with your doctor before taking this medicine if you have high blood pressure or have had problems with depression.
  • A rare side effect caused by fenfluramine is called pulmonary hypertension, or high blood pressure in the lungs. Most people will not have this problem, but if you start to have trouble breathing or easily become short of breath, have chest pain, or swelling in your feet or lower legs call your doctor right away. This is a very serious problem.
  • Fenfluramine can be habit-forming. You may have withdrawal symptoms such as a depressed mood, tiredness, or anxiety after you stop taking the medicine.
  • If you have taken this medicine for a long time, do not suddenly stop taking it. Talk to your doctor first. You may need to take smaller and smaller doses before you completely stop taking the medicine.
  • If the medicine does not seem to work as well after a few weeks, talk to your doctor. You should not use more of it than your doctor prescribed.
  • This medicine may make you dizzy or sleepy Be careful if you are driving a car or using machinery.
  • Talk with your doctor before taking this medicine if you are pregnant or breastfeeding.
  • Tell your doctor or dentist that you are taking fenfluramine before having any kind of surgery.
  • This medicine works best if you follow a low-calorie diet and exercise regularly.

Possible Side Effects While Using This Medicine

Call your doctor right away if you notice any of these side effects:

If you notice these less serious side effects, talk with your doctor:

If you notice other side effects that you think are caused by this medicine, tell your doctor.

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

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