Seizure medicines do cause unwanted side effects in some people. Most of the time, the effects are mild and short-lasting and can be treated by properly adjusting the dosage (the amount taken and the time of each dose).

What are some common side effects from seizure medicines?

You may experience some fatigue, abdominal discomfort, dizziness, or blurred vision during the first weeks of taking these medicines. But if the medication is started at a low dose and increased slowly, and if you are aware of what to expect, these effects are usually tolerable. They probably will stop after several weeks or months, as tolerance develops.

Different seizure medicines tend to produce different types of side effects. To find out what effects are most common with your medication, find it on our list of seizure medicines. Just because a certain effect is common with your medication, however, does not mean that you will experience it. Many people have few or no problems with side effects.

Can seizure medicines cause allergic reactions?

Allergic reactions to seizure medicines are infrequent but they do occur, usually within the first 6 months of starting the medication. The most common type of allergic reaction is a rash.

What unpredictable side effects can occur?

Unpredictable side effects that are not related to the dosage or level of medication in the blood are referred to as idiosyncratic. These can include:

• Rash
• Inflammation or failure of the liver or pancreas
• A serious reduction in the number of white blood cells (needed to fight infection)
• A serious reduction in the number of platelets (needed to control bleeding)

Dangerous and potentially fatal rare reactions include aplastic anemia (severe damage to bone marrow causing a failure in the production of blood cells) and liver failure. There is no reliable way to predict who is most likely to experience these problems. Routine monitoring for them would be both costly and unproductive. If all patients had monthly blood monitoring, some cases of these disorders would still go undetected and hundreds of thousands of patients would undergo unnecessary testing.

A better approach is for your doctor or nurse to explain to you the symptoms that might indicate the beginning of one of these serious side effects. Then if you notice one of these symptoms, you can arrange to be checked right away. Remember, though, that these serious side effects are very rare, so there is probably a much less serious explanation for your symptoms. Don't stop taking your medication unless your doctor tells you to. Your risk of harm from a seizure is greater than the risk of these disorders.

Some seizure medicines are known to present a greater risk of certain serious idiosyncratic or allergic reactions. To see whether you need to look out for a particular problem, find your medicine on our list of seizure medicines and read "What are the most serious side effects?" Keep in mind, though, that nearly all of these serious conditions are quite rare.

What should I do if I develop a rash while using a seizure medicine?

Contact your doctor immediately if a rash or troublesome itchiness develops after a new medication is prescribed. Drug rashes most commonly begin 5 to 18 days after a medication is started. If you are taking more than one medication, the one that was started most recently has probably caused the rash, although rashes may also be caused by a variety of unrelated factors. Most rashes are rather trivial and they usually disappear quickly if the medication is stopped, but you should always tell your doctor right away if a rash begins, because occasionally they can be very serious.

What other side effects call for immediate consultation with a doctor?

Inform a doctor immediately if you experience sores, blisters, or ulcers in your mouth; skin blisters; excessive bleeding; abdominal pain and tenderness; hair loss; fever; unusual infections; or other unusual symptoms while taking a seizure medicine.

What happens when the blood levels of a seizure medicine get too high?

When the level of a medication in a person's blood becomes too high, troublesome effects may occur. The doctor may refer to this problem as toxicity. The dosages or blood levels that cause toxicity with any particular medicine vary from person to person.

What are some side effects related to the dosage of seizure medicines, and how can they be reduced?

Common undesirable effects that may be caused by too high a level of medication (toxicity) include abdominal discomfort, blurred vision, headache, and fatigue. Fortunately, these effects are almost never dangerous or permanent. The doctor can usually reduce or eliminate them by advising changes in when or how you take the medication, lowering the total daily dose, or, when necessary, stopping the medication altogether.

Do seizure medicines impair mental processes?

Seizure medicines act by reducing the excitability of nerve cells in the brain. They can also dampen normal activity and impair cognitive function -- things such as attention and concentration, energy level, mood, drive (the will to do things), and mental and motor speed on tests.

Under what circumstances are seizure medicines most likely to cause impaired thinking?

Problems with mental processes like thinking and memory are most likely to occur when two or more medicines are used together (polytherapy) and when levels of medication in the blood are very high. Improvement is likely if the number of medications is reduced.

Read more about the effects of epilepsy and seizure medicines on mental processes in the section of epilepsy.com called Thinking and Behavior.

Is it true that some seizure medicines can cause bone loss?

Bone loss from certain seizure medicines may be more common than generally believed by doctors and patients. If you take carbamazepine (Tegretol, Carbatrol), phenobarbital, phenytoin (Dilantin, Phenytek), primidone (Mysoline), topiramate (Topamax), or valproate (Depakote), you should consider taking calcium and vitamin D supplements. Check with your neurologist or family doctor about appropriate doses. If you may be pregnant, you should avoid very high doses of vitamin D. Regular exercise is also important for good bone health.

Do the risks of taking seizure medicines outweigh the benefits?

No. In almost every case, when a doctor recommends treatment with seizure medicines, the benefits clearly outweigh the risks. Fewer than 2 people in 150,000 who take seizure medicines will die as a result; the chance of dying in a motor vehicle accident is much greater. The more serious risks include rashes that cause peeling of the skin, infection resulting from a low white-blood-cell count, serious bleeding resulting from a low platelet count, and liver damage. These are very uncommon. Most undesirable side effects of seizure medicines are short-lasting and reversible. In rare cases, however, seizure medicines can actually worsen seizures.

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed:12/15/06