Aspirin, also known as acetylsalicylic acid, is one of the most widely used medications in the world. For decades, it has been routinely recommended for the prevention of heart attack and stroke. However, in recent years, recommendations around aspirin use have changed significantly. Health organizations are now much more cautious about recommending aspirin due to mounting evidence of the risks and side effects.
What is aspirin and how does it work?
Aspirin belongs to a class of medications called non-steroidal anti-inflammatory drugs (NSAIDs). It works by inhibiting an enzyme called cyclooxygenase which produces prostaglandins – chemicals that promote inflammation, pain, and fever.
By preventing prostaglandins from forming, aspirin reduces inflammation, pain, and fever. It also interferes with platelets – cell fragments in the blood that allow clots to form. This “blood thinning” effect helps prevent heart attacks and strokes which are often caused by blood clots.
When was aspirin routinely recommended for preventing heart attack and stroke?
Back in the late 1980s, large clinical trials demonstrated that aspirin could reduce the risk of a first heart attack in men. In these initial studies, the benefits of aspirin were found to outweigh the risks of side effects like gastrointestinal bleeding.
Based on this evidence, many major health organizations started recommending aspirin to prevent cardiovascular disease. For example, in 1997 the US Food and Drug Administration approved labeling that promoted aspirin for prevention of heart attack in men.
Over the following decades, the recommendations expanded to include aspirin for stroke prevention and for both men and women. Millions of healthy adults began taking daily aspirin even though they had never had a heart attack or stroke.
When did recommendations start to change?
In the 2010s, several new studies caused experts to re-evaluate the widespread use of aspirin for prevention. While aspirin remained beneficial for secondary prevention (preventing recurrent events in people with known heart disease), its value for primary prevention (first events) was called into question.
Some key studies that triggered the reassessment of aspirin use were:
- A government-funded study published in 2009 found that aspirin did not lower heart attack or stroke risk in people with no history of cardiovascular disease.
- A large 10-year Japanese trial reported in 2014 that daily aspirin did not prevent serious cardiovascular events but did increase risk of bleeding.
- A 2018 meta-analysis found minimal benefit of aspirin for healthy older adults but significantly higher bleeding risk.
These and other studies suggested the risks of bleeding on aspirin likely outweighed the smaller than expected benefits in low risk individuals. As a result, recommendations evolved to be more conservative about aspirin use for prevention.
What are the current guidelines on aspirin use?
Here is a summary of the latest recommendations from major health authorities:
| Organization | Recommendation |
|---|---|
| US Preventive Services Task Force | Against routine aspirin use for primary prevention of cardiovascular disease in adults 60 years or older. Insufficient evidence for younger adults. |
| American Heart Association | Low-dose aspirin should be considered for primary prevention only in select high risk adults aged 40-70 who are not at increased bleeding risk. |
| American College of Cardiology | Aspirin should generally be avoided in people over 70 for primary prevention. Consider for select adults 40-70 at higher cardiovascular risk. |
| European Society of Cardiology | Aspirin is no longer recommended for individuals without cardiovascular disease due to bleeding risks. |
As shown, most organizations now agree that for healthy adults with no history of heart disease or stroke, the risks of bleeding generally outweigh the potential benefits. Aspirin is only selectively recommended for primary prevention in certain higher risk middle-aged adults.
What are the risks and side effects of aspirin?
While aspirin can help prevent blood clots, it also increases the risk of bleeding. Some of the main risks and side effects of aspirin include:
- Gastrointestinal bleeding – The most common side effect, ranging from minor irritation to bleeding ulcers and hemorrhage.
- Stroke due to hemorrhage – Aspirin prevents clot-caused stroke but may increase risk of bleeding in the brain.
- Brain and other bleeding – Increased risk of brain, intestinal, and other bleeding episodes.
- Allergic reaction – Some people are allergic to aspirin and experience rash, facial swelling, and breathing problems.
- Kidney disease – Long-term aspirin use increases risk of chronic kidney disease.
- Hearing loss and tinnitus – Possible complications of regular aspirin use.
Bleeding risks increase with age and are heightened by other drugs or conditions that can thin the blood or damage the stomach lining. For older adults who are already at higher risk of falls and fractures, the added bleeding hazards with aspirin become even more concerning.
Who should still take aspirin for primary prevention?
Current guidelines agree that aspirin should not be used for primary prevention in people over 70. The bleeding risks are too high compared to the potential cardiovascular benefits.
For adults aged 40-70 with no history of heart disease or stroke, aspirin may be considered on an individual basis. Candidates for primary prevention aspirin tend to have:
- Multiple cardiovascular risk factors like smoking, obesity, high blood pressure
- High calculated risk scores for cardiovascular events
- Family history of early heart disease
- No increased bleeding risks like stomach ulcers or bleeding disorders
For adults younger than 40, there is very little evidence to support routine aspirin use. Individuals at high inherited risk may be exceptions.
It’s important to weigh all risks and benefits with a healthcare provider when deciding on aspirin for primary prevention. Many experts argue the threshold for net benefit from aspirin is quite high.
Key considerations for aspirin use include:
- Cardiovascular risk factors and calculated cardiovascular event risk score
- Bleeding risks including age, gastrointestinal conditions, concomitant medications
- Lifetime bleeding risk with daily aspirin which accumulates over years
- Individual preferences like risk tolerance and ability to adhere to daily medication
What about aspirin for secondary prevention?
In individuals with established heart disease or stroke, the benefit-risk analysis of aspirin changes substantially. Unlike primary prevention, there is very clear evidence that ongoing aspirin prevents recurrent cardiovascular events like heart attack, stroke, and cardiovascular death.
Current guidelines uniformly recommend lifelong aspirin therapy for secondary prevention, assuming no contraindications to aspirin exist. These include:
- History of heart attack or angina
- History of ischemic stroke or mini-stroke (TIA)
- History of stents placed in heart arteries
- History of coronary artery bypass surgery
The bleeding risks with aspirin are still present. But since the baseline cardiovascular risks are so much higher in these patients, the benefits of clot prevention clearly justify the medication for secondary prevention.
Conclusion
In summary, aspirin is no longer routinely recommended for primary prevention of cardiovascular disease due to bleeding risks. It is only suggested on a selective basis in certain middle-aged adults at higher cardiovascular risk.
However, for patients with known heart disease and stroke, the benefits of aspirin for secondary prevention still clearly outweigh the risks. Lifelong aspirin therapy remains firmly indicated in these higher risk individuals.
All decisions around aspirin for primary or secondary prevention must balance cardiovascular risk factors, bleeding risk factors, and individual preferences. Public health guidance has appropriately evolved to be more conservative about aspirin use for primary prevention given the totality of evidence.
But aspirin remains a cornerstone medication following heart attack, stroke, stent placement, and bypass surgery. For these higher risk patients, aspirin continues to save lives by preventing recurrent fatal and disabling cardiovascular events.