SIDE EFFECTS: Headache, nausea, and diarrhea may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: mental/mood changes (such as agitation, slowed thinking, confusion, hallucinations), dizziness, drowsiness.

Tell your doctor immediately if any of these rare but serious side effects occur: change in the amount of urine, yellowing eyes/skin, easy bruising/bleeding.

A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the Famvir (famciclovir) Side Effects Center for a complete guide to possible side effects »

PRECAUTIONS: Before taking famciclovir, tell your doctor or pharmacist if you are allergic to it; or to penciclovir; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: kidney problems.

This drug may rarely make you dizzy or drowsy. Do not drive, use machinery, or do any activity that requires alertness until you are sure you can perform such activities safely. Limit alcoholic beverages.

This medication may contain lactose. If you have certain conditions such as galactose intolerance, severe lactase deficiency (not lactose or milk intolerance), or glucose-galactose malabsorption that require you to restrict your intake of lactose, consult your doctor or pharmacist before taking this medication.

Kidney function declines as you grow older. This medication is removed by the kidneys. Older adults may be more sensitive to the side effects of this drug, especially dizziness, drowsiness, confusion, and change in the amount of urine.

Famciclovir does not protect against the spread of genital herpes. To lower the chance of giving herpes to your partner, do not have sexual contact during an outbreak or if you have symptoms. You can spread genital herpes even if you do not have symptoms. Therefore, always use an effective barrier method (latex or polyurethane condoms/dental dams) during all sexual activity. Consult your doctor or pharmacist for more details.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

It is not known if this medication passes into breast milk. It may have undesirable effects on a nursing infant. Consult your doctor before breast-feeding.