Dilantin Side Effects — What You Need to Know

If you take Dilantin (phenytoin) or are about to start it, you probably want a straight answer: what side effects should you watch for, and when do you need to call your doctor? This page explains the common reactions, the dangerous ones to report fast, how the drug interacts with other medicines, and simple steps to stay safer while using it.

Common side effects

Many people on Dilantin feel fine, but some notice predictable effects. The most common are dizziness, drowsiness, and unsteady walking. You might see blurred vision or involuntary eye movements (nystagmus) when levels are a bit high. Long-term use can cause gum overgrowth (gingival hyperplasia) and excess hair growth. Some users report mild nausea, constipation, or a rash that isn’t severe.

These issues are often manageable. Brushing and flossing more, seeing a dentist regularly, and telling your clinician about fatigue or balance changes can help. Your provider may adjust the dose if side effects are linked to high blood levels.

Serious risks, monitoring & tips

There are a few side effects you must not ignore. A spreading skin rash, fever, sore throat, yellowing skin or eyes, unusual bruising, severe tiredness, or breathing trouble can be signs of a serious reaction or blood problems. Call your doctor or seek emergency care right away if you get any of those.

Dilantin affects the liver and blood counts in some people. Your provider will usually order blood tests early and periodically — checks for liver enzymes, blood cell counts, and drug levels. Because Dilantin interacts with many medicines, tell every clinician and your pharmacist you’re taking it.

This drug speeds up liver enzymes (it’s a strong enzyme inducer). That can lower the effectiveness of oral birth control, warfarin, some statins, and other anticonvulsants. Over-the-counter and herbal products matter too — for example, St. John’s wort can make Dilantin less effective.

Toxicity can look like prominent drowsiness, slurred speech, poor coordination, confusion, and severe nausea or vomiting. If you notice those, get medical help quickly. Don’t stop Dilantin suddenly; stopping can trigger seizures. Any change should be guided by your prescriber.

If you’re planning pregnancy or become pregnant, speak with your doctor. Phenytoin has known risks for the fetus, and pregnancy needs careful planning and monitoring. For long-term users, bone thinning is a concern — your clinician may recommend calcium and vitamin D and check bone health over time.

Practical tips: take Dilantin with food to reduce stomach upset, keep a list of all your drugs and supplements, attend regular blood tests, practice good dental hygiene, and report any rash or unusual symptoms right away. Talk openly with your prescriber about side effects; dose changes or switching drugs are common ways to reduce trouble.

Have specific symptoms or worries? Ask your pharmacist or doctor — they can check interactions, order the right labs, and help you balance seizure control with side effect management. Staying informed and keeping an open line with your care team makes a big difference.