[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/) › Fenfluramine

# Fenfluramine

## Antiseizure medicines?

Antiseizure medicines

An old appetite suppressant brought back at low doses for Dravet and Lennox-Gastaut seizures. Heart valves are checked by echocardiogram.

Updated Nov 1, 2026

## Quick facts

**Group**
[Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)

**Target**
Serotonin transporter (SERT) and serotonin receptors

**Used for**
Seizures of Dravet syndrome

**Key effects**
Loss of appetite and weight loss · Diarrhoea

**Monitor**
Echocardiogram before starting · Blood pressure

**ATC**
N03AX26

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

Fenfluramine is an amphetamine derivative that raises extracellular serotonin by preventing its uptake through the serotonin transporter (SERT). It is also an agonist at several serotonin receptors (5-HT2, 5-HT1D, 5-HT2C) and a positive modulator of the sigma-1 receptor; these extra actions may explain why it controls seizures better than other serotonin uptake inhibitors.

- Fenfluramine blocks serotonin uptake by SERT
- Extracellular serotonin rises
- Serotonin and sigma-1 receptors are stimulated
- Fewer seizures in Dravet and Lennox-Gastaut

## Indications

- Seizures of Dravet syndrome [Epilepsy and seizures →](https://durgical.com/en/conditions/epilepsy-and-seizures/)
- Seizures of Lennox-Gastaut syndrome [Epilepsy and seizures →](https://durgical.com/en/conditions/epilepsy-and-seizures/)

## Adverse effects

### Common

- Loss of appetite and weight loss
- Diarrhoea, constipation and vomiting
- Sleepiness, unsteadiness and falls
- Drooling
- Trouble sleeping

### Serious (rare, important)

- Heart valve disease and pulmonary arterial hypertension (the reason it was withdrawn as a diet drug)
- Serotonin syndrome: agitation, fever, sweating, fast heartbeat, stiff or twitching muscles
- Vision changes with halos (glaucoma)
- Suicidal thoughts or behaviour

## Contraindications

- Known heart valve disease or pulmonary arterial hypertension

## Key interactions

**Serotonergic products (dextromethorphan, St John's wort, tryptophan)**
Higher risk of serotonin syndrome

**Stiripentol with clobazam**
Higher fenfluramine exposure; the treating team adjusts the regimen

**Alcohol and other sedatives**
More drowsiness

## What is monitored

- Echocardiogram before starting, every 6 months during treatment and once 3 to 6 months after the last dose
- Weight and growth in children
- Blood pressure
- Mood and suicidal thoughts

## Administration and safety

- Oral solution; can be given through a nasogastric or gastric tube as instructed
- Raised gradually, not more often than once a week
- In some countries it is dispensed only through a restricted safety programme
- Not stopped suddenly: withdrawal can bring new or worse seizures

## Pregnancy and breastfeeding

There is little information in pregnancy; it is a decision for the treating team.

## Nursing care

- Make sure the echocardiograms are booked and done
- Teach the signs of heart or lung trouble: breathlessness, chest pain, swollen ankles, fainting
- Weigh the child at each visit and report weight loss
- Review cough syrups and supplements for serotonergic products

## Pharmacokinetics

**Absorption**
Orally bioavailable

**Metabolism**
In the liver to norfenfluramine, mainly by CYP1A2, CYP2B6 and CYP2D6

## Memory aid

«FENfluramine: FEN = Feel the Echo Now»: an echocardiogram before, during and after treatment.

## Test yourself

Think of the answer, then tap the question to see it.

## Why was fenfluramine withdrawn as an appetite suppressant?

Because of heart valve disease and pulmonary arterial hypertension.

## Which test is repeated during fenfluramine treatment?

Echocardiography, before starting, during treatment and after the last dose.

## Which two epilepsy syndromes is low-dose fenfluramine used for?

Dravet syndrome and Lennox-Gastaut syndrome.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/fenfluramine/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 4

- [Stiripentol](https://durgical.com/en/pharmacology/stiripentol/)
- [Cannabidiol](https://durgical.com/en/pharmacology/cannabidiol/)
- [Clobazam](https://durgical.com/en/pharmacology/clobazam/)
- [Valproic acid](https://durgical.com/en/pharmacology/valproic-acid/)

## Related conditions 1

- [Epilepsy and seizures](https://durgical.com/en/conditions/epilepsy-and-seizures/)

[← Back to the class: Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Fenfluramine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a620045.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N03AX26) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/fenfluramine/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/fenfluramine/