Antiepileptic drugs, sometimes called antiseizure or anticonvulsant drugs, are a class of medications used in the treatment of epilepsy and other brain-based disorders. They are thought to prevent migraines by increasing levels of the neurotransmitter GABA, which helps to suppress the spreading cortical depression (abnormal electrical activity in the visual cortex of the brain) that triggers a migraine attack. In clinical studies, several AEDs have demonstrated an ability to reduce both the frequency and intensity of migraine attacks.

While there are a number of AEDs prescribed as migraine preventatives, only divalproex sodium valproate (Depakote) and topiramate (Topamax) have been approved for this use by the U.S. Food and Drug Administration. Other AEDs that are not FDA approved but are sometimes prescribed “off-label” for the prevention of migraine include gabepentin (Neurontin), carbamazepine (Tegretol), phenytoin (Dilantin), and lamotrigine (Lamictal).

If you and your doctor decide that one of the AED drugs are a good choice for you, you will be started on a low dose that is gradually titrated, or increased, in order to minimize side effects and find the optimal dosage level. This may occur over a period of weeks or even months. When starting on an AED, it's important to maintain your headache diary carefully so you can gauge how effective the treatment is and document what side effects, if any, you are experiencing.

Fatigue, paresthesia (tingling of the hands and/or feet), and dizziness are common side effects of Topamax. So are gastrointestinal issues such as nausea and diarrhea, and related weight loss. Other less common side effects include depression, anxiety, insomnia, vision problems, and difficulty concentrating.

A rare but serious side effect of Topamax is a condition known as metabolic acidosis, where bicarbonate levels in the blood become elevated. Symptoms include hyperventilation, irregular heartbeat, fatigue, loss of appetite, and mental confusion.

Side effects of Depakote may include hair loss, nausea and vomiting, weight gain, weakness, dizziness, tremor, and sleepiness. Depakote is a central nervous system (CNS) depressant, so it should not be taken with other CNS depressants, including alcohol. Increased levels of ammonia in the blood can occur in some people taking Depakote, which can cause lethargy, vomiting, and a change in mental status. The drug may also cause thrombocytopenia, or a low blood platelet count. Periodic blood tests may be required to monitor for these conditions in patients taking Depakote.

Some side effects of AED drugs can mask the presence of other health conditions. Always tell your doctor about any side effects you experience in conjunction with your migraine medication, whether you're just starting out on the drug or have been taking it for some time.

If you have existing kidney or liver problems, AED drugs may not be an appropriate treatment choice for your migraines. People with urea cycle disorders should not take Depakote because of the risk of hyperammonemic encephalopathy, excessive levels of ammonia in the bloodstream that lead to swelling of the brain. Depending on the drug you are prescribed, you may have to undergo regular blood tests to ensure that your liver function and/or blood values remain healthy.

AEDs should not be used during pregnancy if at all possible. For example, Depakote ingestion during pregnancy has been associated with neural tube and other birth defects.

If you already take prescription drugs, supplements, or over-the-counter medications for migraines or to treat other health conditions, make sure your doctor is aware. AEDs may interact with these sub-stances, causing serious side effects or affecting the potency of one or more drugs. For example, barbiturates, or combination analgesics containing barbiturates, can interact with valproate and potentially cause serious neurological complications.