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Side Effects of Phenytoin
Some of the most common side effects of phenytoin seen in clinical studies include slurred speech, muscle coordination problems, unusual eye movements, and confusion. While most phenytoin side effects are minor and don't require medical attention, some are potentially serious and should be reported to a healthcare provider right away. Notify your healthcare provider if you develop worsening seizures, unusual behavior or thinking, or high blood sugar, among other serious side effects.
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As with any medicine, side effects are possible with phenytoin (Dilantin®); however, not everyone who takes the medication will experience side effects. In fact, most people tolerate it quite well. If side effects do occur, in most cases they are minor and either require no treatment or can easily be treated by you or your healthcare provider.
(This article covers many, but not all, of the possible side effects with phenytoin. Your healthcare provider can discuss a more complete list of phenytoin side effects with you.)
Phenytoin has been studied thoroughly in clinical trials. In these studies, the side effects that occur in a group of people taking the drug are documented and are then compared to side effects that occur in another group of people not taking the medicine. This way, it is possible to see what side effects occur, how often they appear, and how they compare to the group not taking the medicine.
In these studies, some of the most common side effects of phenytoin included:
- Unusual eye movements
- Muscle coordination problems
- Slurred speech
- Confusion.
Other possible side effects can include:
- Dizziness
- Insomnia (see Dilantin and Insomnia)
- Nervousness
- Twitching
- Headaches
- Nausea, vomiting, or constipation
- Larger or fuller lips
- Problems with the gums (including swelling, tenderness, and unusual growth)
- Excessive body or facial hair.
Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD