Fenfluramine is used to control seizures in children from 2 years of age and older with Dravet syndrome (a disorder that begins in early childhood and causes seizures and later may lead to developmental delays and changes in eating, balance, and walking).

Fenfluramine is in a class of medications called anticonvulsants. It is not known exactly how fenfluramine works, but it increases the amount of natural substances in the brain that may reduce seizure activity.

Side Effects Of Fenfluramine

Fenfluramine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • diarrhea
  • constipation
  • vomiting
  • unsteadiness or problems with walking
  • drooling or excessive saliva
  • difficulty falling asleep or staying asleep
  • falls
  • fever, cough, or other signs of infection

Some side effects can be serious. If you experience any of these symptoms or those listed in the WARNINGS AND PRECAUTIONS sections, stop taking fenfluramine and call your doctor immediately or get emergency medical treatment:

  • agitation, hallucinations, fever, sweating, confusion, fast heartbeat, chills, muscle stiffness or twitching, loss of coordination, nausea, vomiting, or diarrhea
  • blurred vision or vision changes, including seeing halos (blurred outline around objects) or colored dots
  • Fenfluramine can cause loss of appetite and weight loss. If you notice your child is losing weight, call your doctor. Your doctor will watch your child’s growth and weight carefully. Talk to your doctor if you have concerns about your child’s growth or weight while he or she is taking this medication.

Fenfluramine may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking fenfluramine:

  • tell your doctor and pharmacist if you are allergic to fenfluramine, any other medications, or any of the ingredients in fenfluramine oral solution. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
  • tell your doctor if you are taking or receiving the following medications or have stopped taking them in the past 14 days: monoamine oxidase (MAO) inhibitors including isocarboxazid (Marplan), linezolid (Zyvox), methylene blue, phenelzine (Nardil), selegiline (Eldepryl, Emsam, Zelapar), and tranylcypromine (Parnate). If you stop taking fenfluramine, you should wait at least 14 days before you start to take an MAO inhibitor.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: antidepressants such as bupropion (Aplenzin, Wellbutrin); medications for anxiety; cyproheptadine; dextromethorphan (found in many cough medications; in Nuedexta); efavirenz (Sustiva); lithium (Lithobid); medications for mental illness; medications for migraine headaches such as almotriptan (Axert), eletriptan (Relpax), frovatriptan (Frova), naratriptan (Amerge), rizatriptan (Maxalt), sumatriptan (Imitrex), and zolmitriptan (Zomig); omeprazole (Prilosec); rifampin (Rifadin, Rimactane, in Rifamate, in Rifater); sedatives; medications for seizures such as carbamazepine (Carbatrol, Equetro, Tegretol, Teril), clobazam (Onfi, Sympazan), phenobarbital, phenytoin (Dilantin, Phenytek), and stiripentol (Diamcomit); selective serotonin-reuptake inhibitors such as fluoxetine (Prozac, Sarafem, Selfemra), fluvoxamine (Luvox), paroxetine (Brisdelle, Paxil, Pexeva), and sertraline (Zoloft); serotonin–norepinephrine reuptake inhibitors (SNRI) such as desvenlafaxine (Khedezla, Pristiq), duloxetine (Cymbalta), levomilnacipran (Fetzima), milnacipran (Savella), and venlafaxine (Effexor); sleeping pills; tranquilizers; trazodone; and tricyclic antidepressants (‘mood elevators’) such as desipramine (Norpramin) or protriptyline (Vivactil). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with fenfluramine, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
  • tell your doctor what herbal products and nutritional supplements you are taking, especially St. John’s wort and tryptophan.
  • tell your doctor if you have or have ever had have glaucoma (increased pressure in the eye that may cause vision loss) or high blood pressure. Also, tell your doctor if you have or have ever had depression, mood problems, suicidal thoughts or behavior or kidney or liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking fenfluramine, call your doctor.
  • you should know that fenfluramine may make you drowsy and make it difficult for you to perform activities that require alertness or physical coordination. Do not drive a car or operate machinery until you know how this medication affects you.
  • ask your doctor about the safe use of alcoholic beverages and medications containing alcohol (cough and cold products, such as Nyquil, and other liquid products) while you are taking fenfluramine. Alcohol can add to the drowsiness caused by this medication.
  • you should know that your mental health may change in unexpected ways and you may become suicidal (thinking about harming or killing yourself or planning or trying to do so) while you are taking fenfluramine. A small number of adults and children 5 years of age and older (about 1 in 500 people) who took anticonvulsants, such as fenfluramine, to treat various conditions during clinical studies became suicidal during their treatment. Some of these people developed suicidal thoughts and behavior as early as one week after they started taking the medication. You and your doctor will decide whether the risks of taking an anticonvulsant medication are greater than the risks of not taking the medication. You, your family, or your caregiver should call your doctor right away if you experience any of the following symptoms: panic attacks; agitation or restlessness; new or worsening irritability, anxiety, or depression; acting on dangerous impulses; difficulty falling or staying asleep; aggressive, angry, or violent behavior; mania (frenzied, abnormally excited mood); thinking about harming or killing yourself, or planning or trying to do so; or any other unusual changes in behavior or mood. Be sure that your family or caregiver knows which symptoms may be serious so they can call the doctor if you are unable to seek treatment on your own.

Fenfluramine Dosage

Fenfluramine comes as a solution (liquid) to take by mouth. It is usually taken two times a day with or without food. Take fenfluramine at around the same times every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take fenfluramine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor will probably start you on a low dose of fenfluramine and gradually increase your dose, not more than once every week.

Use the oral syringe that came with the medication for measuring the solution. Do not use a household spoon to measure your dose. Household teaspoons are not accurate measuring devices, and you may receive too much medication or not enough medication if you measure your dose with a household teaspoon. Rinse the oral syringe with clean tap water and allow it to air dry after each use. Use a dry oral syringe each time that you take the medication.

If you have a nasogastric (NG) or gastric tube, your doctor or pharmacist will explain how to prepare fenfluramine to administer it.

Fenfluramine helps to control seizures but does not cure them. Continue to take fenfluramine even if you feel well. Do not stop taking fenfluramine without talking to your doctor. If you suddenly stop taking fenfluramine, you may experience withdrawal symptoms such as new or worsening seizures. Your doctor will probably decrease your dose gradually.


Do not let anyone else take your medication. Fenfluramine is a controlled substance. Prescriptions may be refilled only a limited number of times; ask your pharmacist if you have any questions.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.