Aspirin might well be considered the top utility player in the medicine cabinet. This cheap over-the-counter drug can be used not only for fever, pain and arthritis, but to prevent heart attack, stroke or angina. It also may reduce the risk of colorectal cancer. Yet aspirin also has side effects worth considering, and its very accessibility may hamper its use.
Aspirin’s anti-clotting and anti-inflammatory abilities protect the heart and blood vessels. The U.S. Preventive Services Task Force “found good evidence that aspirin decreases the incidence of coronary heart disease in adults who are at increased risk for heart disease,” and “strongly recommends that clinicians discuss aspirin chemoprevention with adults who are at increased risk for coronary artery disease.”
Aspirin’s value and potential hazards come from the same source: its ability to prevent the cells in the blood called platelets from clotting. Yet this deceptively simple pill demands caution as well. Aspirin can cause potentially dangerous bleeding in the stomach or brain, but is underprescribed to patients who need it. The USPSTF estimates that of 1,000 people taking aspirin for five years, about two to four middle-aged people, or four to 12 older people, will develop gastrointestinal bleeding and one will have a hemorrhagic (bleeding) stroke.
- Aspirin treatment for primary prevention of heart attacks is safe and worthwhile if the benefits outweigh the risks. When an individual’s risk of a coronary event drops to 0.5 percent a year, the side effects outweigh the benefits to the heart. Physicians can use several simple scales to measure absolute coronary event risk and then help patients decide if aspirin is appropriate therapy.
- A meta-analysis of 16 clinical trials covering 55,462 patients treated for an average of 3 years indicates that aspirin reduces risks of heart attack and ischemic stroke more than it increases the risk of bleeding strokes. Aspirin use prevented 137 heart attacks and 39 strokes for every 10,000 persons taking the drug, with an increase of 12 bleeding strokes.
- Both alcohol and aspirin contribute to gastrointestinal bleeding, but the combination — an aspirin tablet every other day plus three alcoholic drinks a day — increases the chance of bleeding sevenfold. Ibuprofen users who are heavy drinkers also are at increased risk of gastrointestinal bleeding.
- One preliminary study indicates that taking aspirin reduces the risk of some types of breast cancers but not others.
- People who have asthma, uncontrolled high blood pressure, severe liver or kidney disease, bleeding disorders or an allergy to aspirin should not take the drug.
- A recent study of 987,000 people has found no association between aspirin and pancreatic cancer, as had been feared earlier. A preliminary study has shown a decrease in Hodgkin’s lymphoma among users of aspirin. Such studies are suggestive and would need to be confirmed before serving as the basis of recommendations for action.
- Researchers are investigating any protective role for aspirin in preventing other cancers, Parkinson's disease, cognitive decline or dementia.
- The Food & Drug Administration cautions: “Only a doctor can tell you whether the risks of long-term aspirin use may be greater than the benefits.”
- The big questions facing researchers now are: whether higher doses of aspirin offer higher benefits, whether some people somehow don’t respond to aspirin and whether an apparent reduction in cognitive decline seen in self-selected people who take aspirin can be reproduced in randomized controlled trials.
Aspirin is potentially helpful to two types of patients: those who have had a heart attack and those who are at risk. Trying to stop a second heart attack or stroke is called secondary prevention, but between 20 percent and 30 percent of heart attack survivors don’t take aspirin, despite national guidelines.
Furthermore, less than half of those who have never had an attack but who are at risk take aspirin, says Charles H. Hennekens, M.D., of the University of Miami and Florida Atlantic University. Hennekens recommends aspirin for anyone with a 10 percent chance of a heart attack in the next 10 years. The U.S. Preventive Services Task Force calls for it if the risk is 6 percent. An online risk assessment calculator is available at http://hin.nhlbi.nih.gov/atpiii/calculator.asp?usertype=pub.
Paradoxically, aspirin is underused in part because it is cheap and so available. “Aspirin lies outside the usual medical culture,” Hennekens says. “If it were half as effective, 10 times as expensive and required a prescription, doctors would probably prescribe it more often.”
Unlike other anticoagulants, aspirin doesn’t require monitoring, which undercuts the drug’s stature.
“Aspirin is perceived as a ‘trivial’ drug, one that doesn’t carry a lot of weight as a preventive measure,” says University of Iowa psychologist Alan Christensen, Ph.D., a patient compliance expert. “Because aspirin is an over-the-counter drug, patients can start or stop taking it at will.”
A second problem occurs when well-meaning patients take other drugs like acetaminophen or ibuprofen instead of aspirin. These painkillers may work well for headache or muscle discomfort but lack the ability to prevent platelet clotting.
Analysis of the Nurses Health study found that taking aspirin at least twice a week is associated with a 25 percent reduction in risk for colorectal polyps, the precursors to colorectal cancer. Nurses who used more than 14 aspirin tablets a week reduced their risk by half. Other studies have shown similar benefits in men.
Because a greater benefit was shown among those who took higher daily doses, study author Andrew T. Chan, M.D., of Massachusetts General Hospital cautions, the next step is to make aspirin safer, or to pinpoint who will get enough protective benefits to outweigh the risks.
The evidence is not strong enough to recommend aspirin as a preventive measure for colorectal cancer, Chan says. Colonoscopy and sigmoidoscopy are still the most effective ways to prevent that cancer.
But people should not take aspirin regularly without consulting a doctor.
“This is a long-term decision and should be made ... between doctor and patient,” Hennekens says. “Patients should be aware of the benefits and the possible risks.”
Each month, the Health Behavior News Service of the Center for the Advancement of Health brings you Facts of Life: Issue Briefing for Health Reporters, a free publication that provides background on topics within health and behavior as well as names of prominent researchers and physicians willing to be interviewed.