Is taking aspirin (acetylsalicylic acid) 325 milligrams considered a form of blood thinning?

From the Guidelines

Yes, taking aspirin (acetylsalicylic acid) 325 milligrams is considered a form of blood thinning. Aspirin works as an antiplatelet medication, which means it prevents platelets in your blood from sticking together to form clots. When you take a 325 mg dose of aspirin, it irreversibly inhibits an enzyme called cyclooxygenase (COX), which is responsible for producing thromboxane A2, a substance that promotes platelet aggregation. This antiplatelet effect begins within 30 minutes of taking the medication and lasts for the entire lifespan of the affected platelets (approximately 7-10 days) 1.

Key Points to Consider

• Aspirin is commonly used for blood thinning purposes, but it differs from anticoagulants like warfarin or heparin, which work through different mechanisms.
• The antiplatelet effect of aspirin can increase the risk of bleeding, and it may interact with other medications or medical conditions 1.
• The optimum dose of aspirin for preventing cardiovascular disease events is not known, but a dosage of approximately 75 mg/d seems as effective as higher dosages 1.
• Aspirin should be continued indefinitely at a dose of 81 mg to 325 mg daily after PCI, and a loading dose of a P2Y12 receptor inhibitor should be given before the procedure in patients undergoing PCI with stenting 1.

Important Considerations

• You should never start taking aspirin for blood thinning purposes without consulting your healthcare provider, as it can increase your risk of bleeding and may interact with other medications or medical conditions.
• Aspirin can be replaced by oral anticoagulants at the recommended international normalized ratio (INR) if there is an indication for oral anticoagulation (e.g. atrial fibrillation, LV thrombus, mechanical valves) 1.
• The combination of aspirin and oral anticoagulation at INR 2–3 prevented three major adverse events and caused one major bleed per 100 patients treated compared with aspirin alone 1.

From the Research

Aspirin as a Blood Thinner

• Aspirin, also known as acetylsalicylic acid, is commonly used as a blood thinner due to its ability to inhibit platelet aggregation 2, 3.
• The mechanism of action involves the inhibition of platelet cyclooxygenase, which prevents the formation of thromboxane A2, a potent platelet activator 2, 3.
• Studies have shown that aspirin doses as low as 75-100 mg/day can effectively inhibit platelet aggregation and reduce the risk of thrombotic events 4, 5.

Effective Dose of Aspirin

• The optimal dose of aspirin for blood thinning is still uncertain, with different studies suggesting various doses ranging from 75 to 325 mg/day 4, 5.
• A study published in 2006 suggested that 160 mg/day is the most appropriate dose for primary and secondary prevention of stroke and myocardial infarction 5.
• Another study found that 100 mg/day is sufficient for prevention of thrombus formation in the coronary circulation, but higher doses may be required for prevention of vascular events in the cerebral and peripheral circulation 2.

Comparison of Aspirin Doses

• A comparison of every-third-day versus daily low-dose aspirin therapy found that 325 mg every third day and 81 mg daily achieved similar serum thromboxane inhibition 6.
• The study suggested that every-third-day low-dose aspirin regimens could have equal efficacy with reduced toxicity compared to daily low-dose aspirin regimens 6.
• However, the risk of bleeding associated with aspirin use must be carefully considered, particularly in patients with a history of bleeding disorders or those taking concomitant anticoagulant therapy 4, 3.