This medication is not without any side effects, but some side effects such as an upset stomach, drowsiness, dizziness, nausea, diarrhea, and fatigue can be expected as your body adjusts. If you experience the following persistently, consult your doctor: Tingling of arms/legs, Easy bleeding and bruising, Signs of infections such as fever and sore throat, Painful and bloody urine, Severe abdominal pain, Weight loss, Eye pain, vision disruption, Signs of kidney issues, Rash, Persistent vomiting and nausea Allergic reactions to Zyloprim are rare but if you experience symptoms like rashes, itching, swelling, or trouble breathing, inform your specialist immediately.