Side Effects

• Phenytoin can cause side effects such as confusion, memory problems, poor concentration, jerky eye movements, decreased muscle coordination, hand shaking and slurred speech. These effects may be a sign the dosage should be reduced.
  
  

Oher Possible Effects

• Other possible side effects include constipation, dizziness, headaches, insomnia, nausea and vomiting, nervousness and twitching.
  
  

Diabetic Considerations

• Phenytoin can cause elevated glucose levels, so diabetic patients must closely monitor their blood sugar when taking this drug.
  
  

Allergic Reaction

• Some people experience an allergic reaction to phenytoin. Symptoms include difficulty breathing, facial or mouth swelling and a rash or hives. Anyone who develops a rash while taking phenytoin should seek immediate medical attention.
  
  

Long-Term Use

• Long-term use over months or years can cause other side effects. These include weakening of bones, acne, skin darkening, unusual growth or swelling of lips or gums and excessive facial or body hair.