Aspirin is synthesized from salicylic acid and acetic anhydride. Paracetamol (acetaminophen) is made by combining p-aminophenol with acetic anhydride. Both drugs work by inhibiting enzymes called COX (cyclooxygenase), which help produce prostaglandins—the chemicals responsible for pain and inflammation.In the body, aspirin is broken down in the stomach and liver, while paracetamol is mainly metabolized in the liver. If taken in high doses, paracetamol can damage the liver. Common side effects of aspirin include stomach upset, ulcers, and increased risk of bleeding. For paracetamol, side effects are rare at the correct dose but may include allergic reactions or liver damage if abused.