Many people who take Zarontin (ethosuximide) don't report any side effects. Those who do most often complain of digestive problems:

• nausea, upset stomach
• vomiting
• loss of appetite, weight loss
• diarrhea

These problems are usually mild and often they go away by themselves. If they continue or are really bothersome, call the doctor. Usually reducing the amount of Zarontin prescribed or taking it with meals will help. Don't stop taking Zarontin or change the way it's taken without the doctor's guidance.

Other side effects are less common:

• drowsiness
• dizziness
• hiccups
• behavioral changes (irritability, mood change, aggressiveness)

As with the other side effects, tell the doctor if these continue to be a problem. The doctor may suggest a lower dose of Zarontin.

Some patients notice a pinkish or brownish discoloration of their urine. This is unlikely to represent a serious problem.

People who have just started taking Zarontin (or who have just started taking a larger amount) should be careful during activities that might be dangerous, until they know whether they are having any side effects.

Be sure to read about the serious side effects so you will be aware of symptoms that might indicate the beginning of a serious reaction to Zarontin. These serious problems are very rare, but everyone who takes this medicine should at least be aware of them.

Allergic reactions
Some people who take Zarontin have a red rash within the first few weeks of taking it. If this happens, tell the doctor or nurse right away, to be sure that it's not the beginning of a serious problem. It's rare for the rash to be serious, but don't ignore it. It's often necessary to switch to a different seizure medicine.

Reviewed February 2004 by Barry Gidal, PharmD, epilepsy.com Editorial Board.