Allegra Interactions Should I avoid certain foods while taking Allegra?Allegra may interact with the following foods: Very important: A change in your diet, medicine, or dosage may be necessary. Promptly consult your doctor or pharmacist. AVOID GRAPEFRUIT UNLESS MD INSTRUCTS OTHERWISE. Important: Possible changes in your diet, medicine, or dosage should be discussed with your doctor or pharmacist. AVOID APPLE, GRAPEFRUIT AND ORANGE JUICE.