Salicin occurs naturally in willow, not aspirin. It's a prodrug of salicylic acid, which has some anti-inflammatory effects. Aspirin is acetylsalicylic acid. I

Salicin occurs naturally in willow, not aspirin. It's a prodrug of salicylic acid, which has some anti-inflammatory effects. Aspirin is acetylsalicylic acid. It's also a prodrug of salicylic acid, but it has additional anti-inflammatory and anti-thrombotic effects, because unlike salicylic acid itself, it can irreversibly inactivate COX enzymes (enzymes that synthesize compounds needed for inflammation and blood clotting) by acetylating them. It's also less irritating to the digestive system.