Magickal Form: Skin, flesh
On a dark moon, peel the skin off the fruit in one whole piece and hang the skin above a doorway for serious protection. By the full moon, the skin should be completely dried. Remove it and grind to a fine powder. Sprinkle the dust outside your home (at doors and windows) to keep enemies away for good.
Eat the flesh of the grapefruit to promote chastity and heal sexual hang-ups. When eaten during a waning moon (the full moon to the new moon period), it can left the spirits and reenergize the weary.
From Encyclopedia of Magickal Ingredients