Clopidogrel to Prevent Cardiovascular Disease for People Who Have Had Heart Attacks or Strokes

50 for cardiac benefit

Benefits in NNT

1 in 50 were helped (cardiovascular problem prevented)
1 in 77 were helped (non-fatal heart attack prevented)
1 in 200 were helped (non-fatal stroke prevented)
1 in 333 were helped (death prevented)
98% saw no benefit
1.3% were helped by preventing a non-fatal heart attack
0.5% were helped by preventing a non-fatal stroke
0.3% were helped by preventing death

Harms in NNT

1 in 400 were harmed (major bleeding event: required hospital admission and transfusion)
1 in 71 were harmed (rash, compared to aspirin usage)
1 in 91 were harmed (diarrhea, compared to aspirin usage)
0.25% were harmed by a major bleeding event (required hospital admission and transfusion)
1.4% were harmed by rashes (compared to aspirin usage)
1.1% were harmed by diarrhea (compared to aspirin usage)
View As:

Efficacy Endpoints

Heart attack, stroke, death

Harm Endpoints

Bleeding, death


Clopidogrel blocks the action of platelets, reducing the chance of blood clots. Aspirin uses this same mechanism to reduce heart attacks, strokes, and deaths for patients with heart disease and strokes. Because aspirin is inexpensive, effective, and safe, clopidogrel is typically considered only for patients who can't tolerate aspirin because of side effects or allergies. This review examined whether clopidogrel is a suitable replacement for aspirin in people who have known cardiovascular disease.

Clopidogrel and its class of drug were as effective as aspirin in preventing heart attacks, strokes, and deaths in a number of comparative studies (ATTC, 2002). There are minor adverse effects to consider, as clopidogrel and ticlopidine caused more rashes [6.0% vs 4.6%], more diarrhea [4.5% vs 3.4%], and occasional episodes of neutropenia compared to aspirin in one of the largest and best studies.1


Clopidogrel was very similar to aspirin in studies comparing the two and in some narrow categories (stroke) may even be slightly better. However this is speculative and the difference between the two drugs, if real, is extremely small and not likely to be clinically important. In addition, the majority of data suggesting this finding are industry sponsored, and aspirin has proven effective and safe for decades in non-industry trials, making this a more staid and robustly supported first line choice.

*** Important technical note: Based on the very similar performance in comparative trials (see first source study above), it is widely held that aspirin and clopidogrel are essentially equals. However by the time clopidogrel was introduced aspirin was already a proven agent. Therefore it would have been considered unethical not to use aspirin for high risk patients in most settings. This means that there is very little study data comparing clopidogrel alone to a placebo alone for preventing of cardiovascular events. Instead, the addition of either clopidogrel or a placebo to aspirin is more common in studies (see related NNT summaries). Thus our estimates of clopidogrel’s efficacy are projections based on the numbers in our aspirin review, rather than based on existing evidence from studies of clopidogrel.


David Newman, MD


July 8, 2011