Most people who take valproic acid don't have too much trouble with side effects. The most common complaints (usually not too severe) are:

• tiredness (sometimes with slower thinking)
• dizziness
• upset stomach
• vomiting
• tremor (shaking of the hands or other parts of the body
• hair loss
• weight gain
• changes in behavior (depression in adults, irritability in children)

If you notice any of these problems, call the doctor. Sometimes the doctor can help by changing the amount of valproic acid prescribed or prescribing a different valproate medicine. No one should stop taking valproic acid or change the amount they take without their doctor's guidance.

Stomach upset from valproic acid may be less of a problem if it is taken on a full stomach. Stomach upset is more likely when another seizure medicine with similar side effects (for example, Tegretol) is also being used.

Tremor (shaking of the hands or other body parts) tends to be worse when the level of valproate in the blood is highest, a few hours after the pills are taken. Anxiety or caffeine also may make it worse.

Weight gain affects 30% to 50% of people who take valproic acid. It is more common in adult women but can affect anyone. The average gain for adults is 15 pounds. Exercise and a reduced-calorie diet can be very helpful. It's uncertain whether weight gain is greater when higher doses of valproic acid are taken.

Hair loss occurs in 5% to 10% of people who take valproic acid. The hair almost always grows back after the valproic acid is stopped, but it often has a different texture. (For example, it may grow in curly instead of straight.)

People who have just started taking valproic acid (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.

Allergic reactions
Allergic reactions such as rashes are less common with valproic acid and the other valproate medicines than with most other seizure medicines. Even so, you should report any rash to the doctor or nurse right away, especially if treatment has just begun. 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.

A very small number of people who take valproic acid develop life-threatening disorders. Children younger than 2 years of age and other people who are taking more than one seizure medicine have the greatest risk. See Serious side effects.

Long-term side effects
Some people who have taken valproic acid for many years have experienced bone loss and a few other disorders. Taking both calcium and vitamin D may help to prevent this kind of problem. Many doctors recommend a bone density test to identify which people need treatment for bone loss.