Ibuprofen
Ibuprofen is a non-steroidal anti-inflammatory drug. It blocks the cyclooxygenase enzymes and so reduces the production of prostaglandins, which brings down pain, fever and inflammation together. It is used for painful and inflammatory conditions and to lower fever.
Those same prostaglandins protect the stomach lining and help the kidneys manage their own blood flow, which explains most of what follows: it is taken with food, stomach bleeding is its main risk, and existing kidney disease calls for caution. Creatinine, eGFR, hemoglobin and ALT are the values watched during longer use, and slow, unnoticed blood loss from the gut is what drains iron stores. Alcohol, prednisolone and acetylsalicylic acid all add to the bleeding risk, and it is not combined with warfarin or with a second anti-inflammatory such as diclofenac, naproxen or ketorolac. It also interferes with blood-pressure control, so lisinopril, enalapril, losartan and furosemide may not behave as usual alongside it.
Black or tarry stools, vomit that looks like coffee grounds, or stomach pain that keeps returning mean see a doctor rather than switching painkillers at home. Passing much less urine than usual, swelling of the ankles, or growing breathlessness and pallor are the other signs worth acting on.
Reference information, not medical advice. Discuss any change with your doctor.