aspirin use and risk of bleeding complications

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There is a small increase in the incidence of haemorrhagic stroke in patients taking regular aspirin. This effect is larger in patients taking aspirin as a primary prevention of stroke rather than secondary prevention. In neither case is the increased incidence of stroke statistically significant.

There is a significant increase in the rate of extracranial haemorrhage in patients taking aspirin.

Gastrointestinal haemorrhage is a dose-dependent problem:

  • 3% of patients taking 300 mg/day bleed
  • 5% of patients taking 1200 mg/day bleed
  • doses below 100 mg/day are still associated with an increased rate of bleeding - a meta-analysis of 31 trials (n=192,036) identified an approximate three-fold-lower rate of bleeding complications for patients taking aspirin doses of <100mg daily compared with those taking 100–200mg or >200mg doses (1)

Risk of bleeding with particular reference to low dose aspirin (2):

  • relative risk of major gastrointestinal bleeding with low-dose aspirin in a meta-analysis of placebo-controlled trials of vascular protection was 2.07 (95% CI: 1.61-2.66)
    • absolute rate increase with aspirin above placebo was 0.12% per year (95% CI: 0.07-0.19%) with a number-needed-to-harm of 833 patients (95% CI: 526-1429)
    • meta-analysis of aspirin 50-1500 mg daily reported an odds ratio for any gastrointestinal bleeding of 1.68 (95% CI: 1.51-1.88) with an number-needed-to-harm at 1 year of 247
    • relative risk of hospitalization for upper gastrointestinal bleeding with low-dose aspirin in a large Danish cohort study was 2.6 (95% CI: 2.2-2.9) with an absolute annual incidence of 0.6%
    • factors that may increase the risk of gastrointestinal bleeding include prior history of ulcers or gastrointestinal bleeding, corticosteroid use, anticoagulant therapy and addition of a non-aspirin non-steroidal anti-inflammatory drug
    • the author concluded that when determining whether low-dose aspirin is appropriate for an individual patient, the cardiovascular benefit must be weighed against the potential for clinical events such as gastrointestinal bleeding


  1. Serebruany VL, Steinbuhl SR, Berger PB, et al. Analysis of risk of bleeding complications after different doses of asprin in 192,036 patients enrolled in 31 randomised controlled trials. Am J Cardiol 2005;95:1218–22
  2. Laine L. Review article: gastrointestinal bleeding with low-dose aspirin - what's the risk? Aliment Pharmacol Ther. 2006 Sep 15;24(6):897-908

Last reviewed 07/2021