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About phenytoin

Phenytoin is a medicine used to treat epilepsy.

Seizures are bursts of electrical activity in the brain that temporarily affect how it works. Phenytoin slows down these electrical signals to stop seizures.

It can also be used to treat trigeminal neuralgia, a type of nerve pain that affects your face.

Phenytoin can help to relieve nerve pain by slowing down electrical impulses in the nerves and reducing their ability to transmit pain.

Phenytoin is available on prescription. It comes as standard tablets, tablets that can be chewed (Infatabs), capsules and a liquid that you swallow.

Key facts

  • You'll usually take phenytoin once or twice a day. You can take it with or without food.
  • The most common side effects are headaches and feeling dizzy.
  • It takes around 4 weeks for phenytoin to work.
  • If you have epilepsy, it's best to stay on the same brand of phenytoin, as other brands may not work as well for you. If you take it for trigeminal neuralgia, most people do not have to stay on the same brand.
  • You may feel sleepy or dizzy when you first start taking phenytoin or the dose is increased. If this happens to you, do not drive, ride a bike or operate machinery until you feel better.
  • If you have epilepsy, you're entitled to free prescriptions for all of your medicines, not just your epilepsy ones. You'll need a medical exemption certificate from your doctor's surgery.

Page last reviewed: 9 March 2022
Next review due: 9 March 2025