A small daily dose of aspirin is associated with reductions of about one third in cancer. [See References 1-7] .

The reductions may vary according to the cancer, and at present the ecidence is most convincing for bowel cancer.[References 2,3 and 12]

Every drug has undesirable side effects, and with aspirin, this is bleeding. Remember however that aspirin can substantially reduce the risk of serious life-threatening diseases, while the risk of serious bleeding aspirin is rare. Careful studies have shown that in people the benefits of aspirin far outweigh the dangers of bleeding (References 11-13). So do read the section on bleeding in this web site, and do consult the references to some of the published evidence.

A large number of long-term studies have shown that the occurrence of cancer is reduced in the people who take aspirin. [References 1-7].

For example: in an overview of seven trials based on 23,535 people, aspirin taking for five years was associated with a reduction in new cancers of just over 30%.[ 4] Another pooled analysis of 34 trials showed that over a third fewer cancer deaths occurred after five years in the people who had taken daily aspirin.[5] Yet further confirmation of benefit has come from a very large study of women in the USA, in which bowel cancer was reduced by just over 20% in women who took aspirin.[8].

An especially valuable trial was conducted in patients with a genetic condition which carries a very high risk of bowel cancer. There were about half the number of cancers in patients who took aspirin for at least two years compared to patients who took no aspirin.[7].
In 2009 a wide ranging review of evidence from a variety of sources – botanical, animal, human and cellular – was reported. This showed a remarkable consistency in the relationship between aspirin and cancer.[9]

Doctors and health authorities evaluate drugs and other treatments by estimating the balance between the risks (bleeding) and the benefits (reductions in disease. Health authorities also have to take the cost of the treatment into account. A number of careful evaluations of aspirin, have shown its use in older people is highly favourable, with respect to both the risk-benefit balance, and the cost-effectiveness.[10-13]

Finally: a warning! If regular daily aspirin is taken, it should not be stopped suddenly. Suddenly stopping aspirin risks a rebound in vascular risk, and an increase in the risk of death (14). If it has to be stop the drug it should be withdrawn slowly.


  1. Low-dose aspirin and cancer mortality: a meta-analyisis of randomised trials. Amer J Med. 2012; 125:560-7
  2. Effect of aspirin on long-term risk of colorectal cancer: consistent evidence from randomised and observational studies. Lancet 2007;12:1603-13.
  3. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet 2010;376:1741-50.
  4. Effect of daily aspirin on long-term risk of death due to cancer: analysis of individual patient data from randomised trials. Lancet 2011;327:31-41.
  5. Short-term effects of daily aspirin on cancer incidence, mortality and non-vascular death: analysis of thetime course of risks and benefits in 51 randomised trials. Lancet 2012;379:1602-12.
  6. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet 2012;379:1591-601.
  7. Long-term effect of aspirin on cancer in carriers of hereditary colorectal cancer : an analysis from the CAPP2 randomised trial. Lancet 2010;377:2081-7.
  8. Alternate-day low-dose aspirin and cancer risk: long-term observational follow-up of a randomized trial. Ann Int med 2013;159,77-85.
  9. ** Aspirin, salicylates and cancer. Lancet 2009;373:1301-9
  10. ** Estimates of the benefits and harms of prophylactic use of aspirin in the general population. Ann Oncol;2014:
  11. The role of aspirin in cancer prevention. Nat Rev. Clin. Oncol. 2012;9(5):259-267.
  12. ** Effect of including cancer mortality on the cost-effectiveness of aspirin for primary prevention in men. J Gen Intern Med May 2013 (epub ahead of print)
  13. Primary prevention of colortectal cancer with low-dose aspirin in combination with endoscopy: a cost effetive analysis. Gut 2012;61:1172-9

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