Feverfew was traditionally used to treat fevers. It is now commonly used to prevent migraines and treat arthritis. Some research has shown that certain feverfew preparations can prevent migraines. Side effects include mouth ulcers and digestive irritation. People who suddenly stop taking feverfew for migraines may have their headaches return. Feverfew should not be used with nonsteroidal anti-inflammatory medicines because these medicines may change how well feverfew works. It should not be used with warfarin or other anticoagulant medicines.