Many people who take Mysoline (primidone) don't report any side effects. Those who do most often complain of:

• unsteadiness
• the feeling that the surroundings are spinning (vertigo)
• irregular eye movements
• nausea
• vomiting
• blurred or double vision
• drowsiness
• depression

The problems are mild to moderate and usually disappear with time or when the dose is reduced.

Some other side effects mentioned even less often are:

• loss of appetite
• irritability
• acne or other skin lesions
• sexual impotency
• decreased sexual desire
• blood abnormalities
• frozen shoulder

If these problems do not go away within several days, or are really bothersome, call the doctor. Sometimes the doctor can help with these side effects by changing the prescription:

• reducing the overall amount of Mysoline
• changing the amount taken at certain times, such as taking a greater proportion of the Mysoline at bedtime to reduce daytime sleepiness
• prescribing smaller doses, to be taken more often

No one should stop taking Mysoline or change the amount they take or when they take it without their doctor's guidance.

People who have just started taking Mysoline (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 more serious side effects so you will be aware of symptoms that might indicate the beginning of a serious reaction to Mysoline. These serious problems are very rare but everyone who takes this medicine should at least be aware of them.

Reviewed February 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.