Taking an aspirin daily or every other day has become a common health ritual. This is because studies have clearly shown that aspirin keeps the platelets — the small clot-forming particles in the blood — from clumping together ("aggregating"), so as to reduce the likelihood of heart attacks and strokes. But are you sure your daily aspirin is really protecting you?
Possibly not, according to a review and large-scale analysis in the British Medical Journal of 20 studies. According to the authors, between 15 and nearly 30 percent of people taking aspirin were "aspirin resistant;" that is, aspirin was doing nothing to protect them from cardiovascular disease.
Resistance was more common in women than in men, and among those with kidney disease. And, compared to those who do benefit from aspirin's action, the aspirin-resistant ones were almost four times more likely to suffer a heart attack or stroke, and six times more likely to die from such events.
What to do about these findings? First, since 70 percent to 85 percent of people do benefit from aspirin, the authors of the review emphasize that you should continue to take regular aspirin even if you might not be responding to the drug.
You may also be wondering whether you should take a larger aspirin dose, just in case you might be resistant. The answer to this question is "probably not."
The common doses of aspirin used in this country to prevent cardiovascular complications are a baby aspirin (81 mg) daily or a regular aspirin (325 mg) every other day. The reviewers found that resistant patients got no better protection when taking larger doses of aspirin than they did when taking their regular dose — and besides, larger doses are more likely to cause bleeding problems. The study authors emphasize that doctors should discuss these risks with their patients.
One final question: Should you add another anti-platelet drug, such as clopidogrel (Plavix) to your aspirin dose? Again, probably not — the reviewers found that, among aspirin-resistant individuals, those who took clopidogrel along with their aspirin suffered the same number of cardiovascular events as those aspirin resisters who took only aspirin.
Research is needed to develop widely available tests to identify aspirin resistance and to determine what steps resistant people can take to protect themselves against the cardiovascular complications caused by platelet aggregation. Meanwhile, it is important for anyone taking regular aspirin to discuss with their doctors the benefits and the risks of their dose of aspirin.