Antiplatelet medications are used widely to prevent blood clots and cardiovascular disease events. The most commonly used antiplatelet drug is aspirin. Two clinical studies examined the effect of aspirin on blood viscosity and suggested that aspirin may have a viscosity-lowering effect [1, 2]. However, the most authoritative study on the effect of aspirin on blood viscosity was a randomized, double-blind, placebo-controlled study of 100 healthy, nonsmoking, adult males with normal lipid levels, using an automated scanning capillary viscometer. The study showed that aspirin had no significant effect on blood viscosity [3]. 

Using the same automated scanning capillary viscometer, aspirin plus dipyridamole was shown to be more effective than aspirin alone in reducing diastolic blood viscosity in patients with high homocysteine levels and stable cardiovascular disease [4]. Dipyridamole is another more powerful antiplatelet drug. The dipyridamole study was performed as a follow-up study to the European/Australasian Stroke Prevention in Reversible Ischemia Trial (ESPRIT), a randomized controlled trial which showed that combination therapy of aspirin/dipyridamole reduced cardiovascular disease events and death after stroke as compared with aspirin alone [5]. 

Clopidogrel (Plavix) was demonstrated to reduce diastolic blood viscosity values by 18% on average from baseline levels three weeks after administration [6]. Systolic blood viscosity values were also reduced 10% from baseline after the third week (p values < 0.01). These findings were based on a double-blind, placebo-controlled study of 30 age- and gender-matched individuals with impaired blood viscosity and evidence of carotid and/or femoral atherosclerosis. 


Holsworth RE, Cho YI. “Hyperviscosity Syndrome: A Nutritionally-Modifiable Cardiovascular Risk Factor.” Advancing Medicine with Food and Nutrients, Second Edition. Ed. Ingrid Kohlstadt. Boca Raton: CRC Press, 2012. 


1. Bozzo, J., M. R. Hernandez, and A. Ordinas, Reduced red cell deformability associated with blood flow and platelet activation:Improved by dipyridamole alone or combined with aspirin. Cardiovasc Res 1995; 30:725-30. 

2. Bozzo, J., et al., Prohemorrhagic potential of dipyrone, ibuprofen, ketorolac, and aspirin: mechanisms associated with blood flow and erythrocyte deformability. Journal of Cardiovascular Pharmacology 2001; 38:183-190. 

3. Rosenson, R., et al., Aspirin. Aspirin does not alter native blood viscosity. Journal of Thrombosis and Haemostasis 2004; 2:340-1. 

4. Rosenson, R.S., Treatment with aspirin and dipyridamole is more effective than aspirin in reducing low shear blood viscosity. Microcirculation 2008; 15:615-20. 

5. Halkes, P., et al., Aspirin plus dipyridamole versus aspirin alone after cerebral ischaemia of arterial origin (ESPRIT): Randomised controlled trial. Lancet 2006; 367:1665-73. 

6. Ciuffetti, G., et al., Clopidogrel: Hemorheological effects in subjects with subclinical atherosclerosis. Clin Hemorheol Microcirc 2001; 25:31-9.

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