Agent	Safety (percentage of cases)	Tolerability	Effectiveness	Average monthly cost*
Aspirin	Intracranial hemorrhage (0.49%), major bleeding (0.8%), GI bleeding (3%), possible aspirin allergy	GI upset (17.6%)	Stroke, death: NNT = 22 (vs. placebo)	$1 to $2
			Stroke, myocardial infarction, vascular death: NNT = 28 (vs. placebo)
Clopidogrel (Plavix)	Intracranial hemorrhage (0.35%), life-threatening bleeding (1%), GI bleeding (2%)	GI upset (15%), diarrhea (4.5%), rash (6%)	Stroke, myocardial infarction, vascular death: NNT = 196 (vs. aspirin)	$145 ($215)
Aspirin plus clopidogrel	Major bleeding (2%), life-threatening bleeding (3%), possible aspirin allergy	GI upset, diarrhea, rash	No difference in effectiveness vs. aspirin	See above
Aspirin/dipyridamole (Aggrenox)	Intracranial hemorrhage (0.8%), extracranial hemorrhage (1.7%), possible aspirin allergy	Headache (26%), GI upset	Death from all vascular causes, nonfatal stroke: NNT = 33 (vs. aspirin)	$400 ($550)