Can aspirin cause strokes rather than prevent them?

A new study claims that people with known aspirin resistance may be at risk of more severe strokes than people who have a more conventional reaction to the medication. “Aspirin resistance is an important predictor of severe stroke and large stroke size in patients taking aspirin before having a stroke,” lead researcher Dr. Mi Sun Oh of the Hallym University College of Medicine in Seoul, South Korea wrote. Aspirin is a salicylate drug known for its analgesic properties against pain, headache, swelling, and inflammation. Additionally, it has an antiplatelet effect that helps break up blood clots. As such, many doctors prescribe low aspirin doses to patients who are at an increased risk of stroke.

However, Dr. Oh and colleagues found that not only did aspirin fail to keep blood from clotting in 28% of stroke patients who were aspirin resistant, but these patients also had worse strokes than those who weren’t. The South Korean researchers monitored 310 patients who had suffered an ischemic stroke after taking aspirin for a minimum of seven days. Resistance to aspirin was checked within 24 hours of hospitalization. The approximately 86 aspirin resistant patients had strokes ranging between 3 and 11 on a stroke severity score, as opposed to 1 to 6 scores among the rest. Furthermore, strokes in the former group affected an area of the brain two times as large as the latter. The results will be officially presented at the annual meeting of the American Academy of Neurology in Washington, D.C in April.

The findings reveal further aspects of the relationship between aspirin and stroke. “This study fits with this premise (that people who have smaller, less severe strokes as a result of taking aspirin – as previous research has suggested – aren’t resistant to the drug),” chairman of neurology at the University of Miami Miller School of Medicine Dr. Ralph Sacco said, though he admits that the reason for this is not known. “One way aspirin works is to prevent platelets [particles that form clots in the blood] from clumping, and this could mean that clots that are released and block brain arteries are smaller and lead to smaller areas of brain injury,” he theorized.

According to previous studies, up to 45% of people may experience aspirin resistance to some degree, but it is seldom tested for. “Although we do not routinely test for aspirin resistance, in the future era of targeted medicine we may improve the ability to assess whether someone is aspirin-resistant and choose medicines more accurately,” Sacco said. Oh added that “in patients at high risk for stroke with aspirin resistance, different anti-clotting drugs — such as clopidogrel (Plavix) — can be considered as alternatives to prevent another stroke or decrease stroke severity.”