Patient/caregiver instructed Allopurinol reduces the production of uric acid in your body. Uric acid buildup can lead to gout or kidney stones. Take once daily as ordered with a full glass of water. Medication may weaknen your immune system, avoid sick persons. Common side effects are vomiting, diarrhea; drowsiness, headache; changes in your sense of taste; or muscle pain. Notify SN/MD if experiencing bothersome or unusual side effects.