Various factors may limit the effectiveness of aspirin, including:
- Use of enteric-coated aspirin
- Buildup of plaque in blood vessels, causing blood vessel constriction despite the use of aspirin
- Other medications that prevent aspirin from binding to cyclooxygenase receptors, including nonsteroidal anti-inflammatory drugs (NSAIDs), especially ibuprofen
- Other blood-clotting processes or other platelet activation pathways that exert a stronger effect than the antiplatelet effect of aspirin
- Increased platelet turnover
- Cyclooxygenase enzyme genetic mutations
