In Summary, for those who took the aspirin:

Benefits in NNT

  • 97.7% saw no benefit
  • 2.3% were helped by being saved from death
  • 1 in 42 were helped (life saved)

Harms in NNT

  • 0.6% were harmed by a minor bleeding event*
  • 1 in 167 were harmed (non-dangerous bleeding)*

*Blood levels showed anemia but not enough to require transfusion

View As:

Source: ISIS­2: Randomized trial of intravenous streptokinase, oral aspirin, both, or neither among 17187 cases of suspected acute myocardial infarction. Lancet. 1988 Aug 13;2(8607):349-60.

Efficacy Endpoints: Death at 1 month following major heart attack (STEMI)

Harm Endpoints: Major bleeding (brain bleeding or bleeding requiring transfusion) and minor bleeding.

Narrative: The lone high quality trial addressing this question was multi-institutional across the U.S and Western Europe and was a randomized controlled trial of over 17000 subjects. Subjects were believed to be suffering acute MI by treating physicians and were randomized to aspirin, a thrombolytic (‘clot-busting’ medication), both, or neither. The groups were similar. There was increased death in the first month among those assigned to placebo 1016/8600 (11.8%) versus those assigned to aspirin 811/8587 (9.4%) with no significant increase in transfusion or intracerebral hemorrhage. There was a 0.6% increase in minor bleeding.

Aspirin provides among the best mortality benefits of any intervention for MI, with minimal downside. The anti-platelet mechanism seems sensible and the data is strong. Aspirin should be given to all cases of confirmed or suspected STEMI unless a significant contraindication exists.

Caveats: We don’t know for certain that the patients entered into this trial were having heart attacks, as the entry criterion was an EKG showing ST elevation and MI was not confirmed with any other testing (i.e. cardiac biomarkers). There has been no attempt to confirm these results (there probably never were).

Author: Joshua Quaas, MD

Published/Updated: November 28, 2009

  1. The Title Bar

    The title bar is color-coded with our overall recommendation.

    • Green: Benefits outweigh risks.
    • Yellow: Unclear risk/benefit profile.
    • Red: Benefits do not outweigh risks.
    • Black: Obvious harms, no clear benefits.
  2. Tip content...