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Phenytoin

Brand names: Dilantin, Phenytek

Phenytoin is an older seizure medicine. Small dose changes can cause big changes in blood level, so levels are checked.

Brand namesDilantin, Phenytek
Type of medicineAnticonvulsant (seizure medicine)
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

Good dental care is important because it can cause gum overgrowth.

What it's used for

  • Seizures

How to take it

  • Take it at the same times each day. Shake the liquid well.
  • Don't switch brands or forms without asking.
  • Don't stop suddenly; this can trigger seizures. Your provider will lower the dose slowly.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Dizziness
  • Unsteadiness
  • Sleepiness
  • Gum overgrowth
  • Extra body hair
Call 911Rash with blisters, peeling, or fever
Call your provider todaySlurred speech, trouble walking, or uncontrolled eye movements (level too high)
Call your provider todayYellow skin or eyes, or swollen glands with fever
Call 911Thoughts of suicide or harming yourself. Call or text 988 any time.

Warnings

  • Serious skin reactions are more likely with the HLA-B*1502 gene.
  • Long-term use can thin bones; vitamin D may be recommended.

Other medicines, foods, and alcohol

  • It interacts with many medicines, including warfarin, birth control, and other seizure medicines.
  • Tube feedings and antacids can lower absorption.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

It can cause birth defects. Talk with your provider before pregnancy; don't stop on your own.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.