What are side effects of ibuprofen vs paracetamol for an adult?

Stomach pain & more. The most common side effects of Ibuprofen are stomach pain, gastrointestinal ulcers, bleeding, kidney injury, nausea, diarrhea, throat swelling and liver injury. Acetaminophen can cause nausea, headache, kidney injury and liver failure (in overdose). In general, Acetaminophen is far safer an side effects are much less common than with ibuprofen.