This statement summarizes the current U.S. Preventive Services Task Force (USPSTF) recommendation on aspirin for the primary prevention of cardiovascular events and the supporting scientific evidence, and updates the 1995 recommendation contained in the Guide to Clinical Preventive Services, Second Edition¹.

• Decisions about aspirin therapy should take into account overall risk for coronary heart disease. Risk assessment should include asking about the presence and severity of the following risk factors: age, sex, diabetes, elevated total cholesterol levels, low levels of high-density lipoprotein (HDL) cholesterol, elevated blood pressure, family history (in younger adults), and smoking. Tools that incorporate specific information on multiple risk factors provide more accurate estimation of cardiovascular risk than categorizations based simply on counting the numbers of risk factors (http://hp2010.nhlbihin.net/atpiii/calculator.asp).²
• Men older than 40 years, postmenopausal women, and younger people with risk factors for coronary heart disease (e.g., hypertension, diabetes, or smoking) are at increased risk for heart disease and may wish to consider aspirin therapy. Table 1 shows how estimates of the type and magnitude of benefits and harms associated with aspirin therapy vary with an individual's underlying risk for coronary heart disease. Although balance of benefits and harms is most favorable in high-risk people (5-year risk greater than 3 percent), some people at lower risk may consider the potential benefits of aspirin to be sufficient to outweigh the potential harms.
• Discussions about aspirin therapy should focus on potential coronary heart disease benefits, such as prevention of myocardial infarction, and potential harms, such as gastrointestinal and intracranial bleeding. Discussions should take into account individual preferences and risk aversions concerning myocardial infarction, stroke, and gastrointestinal bleeding.
• Although the optimal timing and frequency of discussions related to aspirin therapy are unknown, reasonable options include every 5 years in middle-aged and older people or when other cardiovascular risk factors are detected.
• Most participants in the primary prevention trials of aspirin therapy have been men between 40 and 75 years of age. Current estimates of benefits and harms may not be as reliable for women and older men.
• Although older patients may derive greater benefits because they are at higher risk for CHD and stroke, their risk for bleeding may be higher.
• Uncontrolled hypertension may attenuate the benefits of aspirin in reducing CHD.
• The optimum dose of aspirin for chemoprevention is not known. Primary and secondary prevention trials have demonstrated benefits with a variety of regimens, including 75 mg per day, 100 mg per day, and 325 mg every other day. Doses of approximately 75 mg per day appear as effective as higher doses; whether doses below 75 mg per day are effective has not been established. Enteric-coated or buffered preparations do not clearly reduce adverse gastrointestinal effects of aspirin. Uncontrolled hypertension and concomitant use of other nonsteroidal anti-inflammatory agents or anticoagulants increase risk for serious bleeding.

Epidemiology and Clinical Background

Cardiovascular disease, including ischemic coronary heart disease, stroke, and peripheral vascular disease, is the leading cause of death in the United States.³ Yearly, over 1 million Americans experience new or recurrent myocardial infarction or fatal coronary heart disease. Most events occur in older people and those with recognized risk factors for cardiovascular disease, including high cholesterol, high blood pressure, diabetes, or a history of smoking.

The early-documented and clear success of aspirin in preventing further clinical disease in some patients with known heart disease (secondary prevention) raised interest in aspirin as a potential primary preventive intervention in men and women without known heart disease.⁴ Two early randomized trials of aspirin had conflicting results, however, and lacked sufficient power to estimate major harms, such as gastrointestinal bleeding and hemorrhagic stroke.^{5, 6} Thus, the role of aspirin in primary prevention has remained controversial. The new USPSTF recommendation incorporates additional data from three recent trials and provides more reliable estimates of both benefits and harms of aspirin in patients without known heart disease.

Efficacy of Chemoprevention

Five trials have examined the effects of daily or every-other-day aspirin for the primary prevention of cardiovascular events over periods of 4 to 7 years.^5-9 Most participants were men older than 50 years. Meta-analysis of pooled data from all of the studies showed that aspirin therapy reduced the risk for CHD by 28 percent (summary odds ratio [OR], 0.72; 95 percent CI, 0.60 to 0.87). Summary estimates showed no significant effects of aspirin on total mortality (OR, 0.93; 95 percent CI, 0.84 to 1.02) and stroke (OR, 1.02; 95 percent CI, 0.85 to 1.23).

Harms of Chemoprevention

These five primary prevention trials, and a larger number of randomized controlled trials (RCTs) of secondary prevention that enrolled patients with heart disease or stroke, demonstrate that aspirin increases rates of gastrointestinal bleeding. Estimated rates of major gastrointestinal bleeding episodes are approximately 2 to 4 per 1,000 middle-aged individuals (4 to 12 for older individuals) given aspirin for 5 years.^10-12

These controlled trials in primary and secondary prevention settings also suggest that aspirin increases rates of hemorrhagic strokes by a small amount (0-2 per 1,000 individuals given aspirin for 5 years).^5-7 Such estimates are less reliable than those of gastrointestinal bleeding because few strokes were reported in the trials.

In 1994, the Canadian Task Force on Preventive Health Care concluded that the evidence was not strong enough to recommend for or against use of aspirin for primary prevention of heart disease in men or women and recommended that physicians and patients balance the reduced rate of nonfatal myocardial infarction against potential adverse effects.¹³ In 2000, the American Diabetes Association recommended that clinicians consider aspirin for primary prevention of heart disease in diabetic patients who are older than 30 years or have risk factors for cardiovascular disease and no contraindications to aspirin therapy.¹⁴ In 1997, the American Heart Association concluded that aspirin may be warranted for patients at high risk of myocardial infarction but that health care providers must consider a patient's particular cardiovascular risk profile, the demonstrated benefits of aspirin on reducing risk for a first myocardial infarction, and known as well an unknown side effects of aspirin.¹⁵

In 1998, the European Society of Cardiology recommended low-dose aspirin (75 mg) for patients with well-controlled hypertension and men at "particularly" high risk for coronary heart disease, but not for all individuals at high risk.¹⁶

This document is in the public domain within the United States. Requests for linking or to incorporate content in electronic resources should be sent via the USPSTF contact form.

Source: U.S. Preventive Services Task Force. Aspirin for the primary prevention of cardiovascular events: recommendations and rationale. Ann Int Med 2002;136(2):157-60.

Members of the U.S. Preventive Services Task Force are Alfred O. Berg, M.D., M.P.H., Chair, USPSTF (Professor and Chair, Department of Family Medicine, University of Washington, Seattle, WA); Janet D. Allan, Ph.D., R.N., C.S., Vice-chair, USPSTF (Dean and Professor, School of Nursing, University of Texas Health Science Center, San Antonio, TX); Paul S. Frame, M.D. (Tri-County Family Medicine, Cohocton, NY, and Clinical Professor of Family Medicine, University of Rochester, Rochester, NY); Charles J. Homer, M.D., M.P.H. (Executive Director, National Initiative for Children's Healthcare Quality, Boston, MA); Mark S. Johnson, M.D., M.P.H. (Associate Professor of Clinical Family Medicine and Chairman Department of Family Medicine, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, NJ); Jonathan D. Klein, M.D., M.P.H. (Associate Professor of Pediatrics and of Community and Preventive Medicine, University of Rochester School of Medicine, Rochester, NY), Tracy A. Lieu, M.D., M.P.H. (Associate Professor, Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston, MA); Cynthia D. Mulrow, M.D., M.Sc. (Professor of Medicine, University of Texas Health Science Center, Audie L. Murphy Memorial Veterans Hospital, San Antonio, TX); C. Tracy Orleans, Ph.D. (Senior Scientist, The Robert Wood Johnson Foundation, Princeton, NJ); Jeffrey F. Peipert, M.D., M.P.H (Director of Research, Women and Infants' Hospital, Providence, RI); Nola J. Pender, Ph.D., R.N. (Professor and Associate Dean for Research, School of Nursing, University of Michigan, Ann Arbor, MI); Albert L. Siu, M.D., M.S.P.H (Professor of Medicine, Chief of Division of General Internal Medicine, and Medical Director of the Primary Care and Medical Services Care Center, Mount Sinai School of Medicine and The Mount Sinai Medical Center, New York, NY); Steven M. Teutsch, M.D., M.P.H. (Senior Director, Outcomes Research and Management, Merck & Company, Inc., West Point, PA); Carolyn Westhoff, M.D., M.Sc. (Associate Professor of Obstetrics, Gynecology and Public Health, Department of Obstetrics and Gynecology, Columbia University College of Physicians and Surgeons, New York, NY); and Steven H. Woolf, M.D., M.P.H. (Professor of Family Medicine, Department of Family Practice, Medical College of Virginia, Fairfax, VA).

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Baseline risk for coronary heart disease over 5 years: 1%
Total mortality: No effect
CHD events**: 1-4 avoided
Hemorrhagic strokes***: 0-2 caused
Major gastrointestinal bleeding events****: 2-4 caused

Baseline risk for coronary heart disease over 5 years: 3%
Total mortality: No effect
CHD events**: 4-12 avoided
Hemorrhagic strokes***: 0-2 caused
Major gastrointestinal bleeding events****: 2-4 caused

Baseline risk for coronary heart disease over 5 years: 5%
Total mortality: No effect
CHD events**: 6-20 avoided
Hemorrhagic strokes***: 0-2 caused
Major gastrointestinal bleeding events****: 2-4 caused

* These estimates are based on a relative risk reduction of 28% for coronary heart disease events in aspirin-treated patients. They assume risk reductions do not vary significantly by age.
** Nonfatal acute myocardial infarction and fatal coronary heart disease. Five-year risks of 1%, 3% and 5% are equivalent to 10-year risks of 2%, 6%, and 10%, respectively.
*** Data from secondary prevention trials suggest that increases in hemorrhagic stroke may be offset by reduction in other types of stroke in patients at very high risk for cardiovascular disease (CVD) (greater than or equal to 10% 5-year risk).
**** Rates may be 2 to 3 times higher in people older than 70 years.

Source: Hayden M, Pignone M, Phillips C, Mulrow C. Aspirin for the primary prevention of cardiovascular events: A summary of the evidence for the U.S. Preventive Services Task Force. Annals of Internal Medicine 2002;136:16172.