Serious side effects of acetaminophen requiring medical evaluation include skin rash, itching or hives; yellow eyes or skin; fever; pain in the lower back and sides; and unusual weakness or tiredness, states Mayo Clinic. Other serious side effects include black or bloody stools, cloudy or bloody urine, and unusual bleeding.
Symptoms of an acetaminophen overdose requiring emergency assistance include increased sweating, diarrhea, loss of appetite, nausea or vomiting, and stomach pain, according to Mayo Clinic. Using acetaminophen with certain drugs, such as warfarin, lixisenatide and carbamazepine, can increase the risk of side effects. Patients with liver or kidney disease should consult with their doctors before using acetaminophen due to potential complications.