For decades both aspirin and the anticoagulant warfarin (sometimes known by its brand name Coumadin) have been prescribed to people who have had a stroke caused by blocked blood vessels in the brain to help prevent a recurrence. Currently, neurologists are split over which is better. A team from 59 medical centers around the country studied stroke patients to figure out which of the two pills worked better at preventing a second stroke.

What the researchers wanted to know: Does aspirin or warfarin better prevent the blockage of arteries that can cause stroke?

What they did: The researchers enrolled 569 patients from around the country who had recently had a stroke and had been diagnosed with blocked blood vessels in their brain (called intracranial arterial stenosis). They split them in two groups, with one group receiving warfarin and the other aspirin. The dosage of the warfarin group was adjusted monthly to keep each patient's blood within a certain viscosity. Patients in the aspirin group were given 650 mg twice a day, the equivalent of about four regular tablets. Patients were examined every four months by a neurologist, and the researchers kept track of the number of ischemic (blocked vessel) strokes, brain hemorrhages, and deaths from vascular disease in each group.

What they found: In contrast to some previous studies that have shown that warfarin works better, about 22 percent of the patients in both groups had ischemic stroke, brain hemorrhage, and death from vascular disease. Those rates are much higher than in previous studies, suggesting that the population group they studied—people with blocked cranial vessels—are at especially high risk. However, the study was stopped early because those in the warfarin group, also in contrast to previous studies, had a higher overall death rate (mainly due to cancer), number of hemorrhages, and number of heart attacks. The researchers could not say for sure why the warfarin group fared worse than the aspirin group, though they say some of it could be attributed to chance or to the design of their study. In addition, a huge problem with warfarin was that it was hard for doctors to give a dosage that kept patients' blood within a target viscosity range. When it was within that range (about 63 percent of the time overall), the warfarin was much more effective.

What it means to you: The researchers conclude that aspirin should always be used instead of warfarin to prevent a second stroke in patients with blocked blood vessels in their brain. However, one neurologist, Walter Koroshetz, who commented in the same issue of the journal, was not so sure. He pointed out that some of the adverse effects of the warfarin group could have been due to study design, chance, or the difficulty in finding the right dose of warfarin. Because other studies have not agreed with this one, and this study has some problems, there is no clear clinical recommendation, he says. The one thing that can be concluded from this study, both he and the study author's agree, is that people with intracranial arterial stenosis need aggressive treatment to prevent a second stroke and the progression of vascular disease.

Caveats: This study had a fair amount of complications, including the fact that it was stopped early and, even before its end, 28 percent of the patients in the warfarin group dropped out. In addition, the aspirin dose was about four times as high as is currently recommended for the prevention of a second stroke, so it's not clear how a more typical aspirin dose would stack up against warfarin.

Find out more: The National Institute of Neurological Disorders and Stroke, which funded this study, has basic information about strokes as well as links to more information.

The institute also has information about ways to prevent stroke.

Read the article: Chimowitz, M.I. et al. "Comparison of Warfarin and Aspirin for Symptomatic Intracranial Arterial Stenosis." New England Journal of Medicine. March 31, 2005, Vol. 352, No. 13, pp. 1305–1316.

Abstract online: http://content.nejm.org