Some people have been known to eat the leaves of feverfew to prevent migraine headaches. They eat 1-3 leaves daily, sometimes in between bread. If irritation should occur in your mouth, try eating with bread or eating with other foods, maybe in a salad.
For Feverfew Tea:
You can add 2 teaspoons of fresh leaves or 1 teaspoon of dried leaves to hot boiling water for 15 minutes. Strain out the herbs, and reheat if cooled down too much. Add sugar, honey or lemon to your liking. Drink one cup a day as needed.
A neat tip I have heard, was to add peppermint or spearmint leaves to add extra flavor as well.