Acetylsalicylic acid has analgesic, antipyretic and anti-inflammatory properties, primarily due to the inhibition of the biosynthesis of prostaglandins and thromboxanes from arachidonic acid by irreversible acetylation of the enzyme cyclooxygenase (COX).

Paracetamol has analgesic and antipyretic properties, but unlike acetylsalicylic acid, it does not inhibit platelet aggregation.

Addition of caffeine increases the antinociceptive effects of acetylsalicylic acid and paracetamol.