Aspirin blocks?

Aspirin blocks COX (cyclooxygenase) enzymes—mainly COX-1 (and also COX-2 to some extent)—which reduces production of prostaglandins and thromboxane A₂.

Key effects:

• Anti-inflammatory / pain / fever: ↓ prostaglandins
• Blood thinning (antiplatelet): ↓ thromboxane A₂ → platelets can’t aggregate normally
• Irreversible effect on platelets: aspirin permanently inhibits COX in platelets (they can’t make new COX), lasting for the platelets’ lifespan.

If you meant “Aspirin blocks what symptom?” (e.g., pain, fever, clotting, etc.), tell me and I’ll map it to the exact pathway.