Aspirin is a common medication available over-the-counter that possesses antiplatelet properties, meaning it works to inhibit the aggregation of blood cells called platelets. A stroke is a medical emergency that occurs when blood flow to a part of the brain is interrupted, typically by a blockage or a rupture. Given the drug’s effect on blood clotting, its use has long been investigated as a way to prevent the formation of the clots that cause the most common type of stroke. Understanding the current medical evidence is crucial for determining aspirin’s role in reducing stroke risk.
Preventing the First Stroke (Primary Prevention)
Primary prevention refers to the practice of taking aspirin to avoid a stroke or heart attack in individuals who have never experienced such an event. For this population, the decision to use aspirin is complex and involves a careful balancing act between a potential reduction in clot-related events and an increased chance of internal bleeding. Recent large-scale clinical trials and subsequent medical guidelines have substantially shifted the consensus for healthy adults.
Current recommendations generally advise against starting low-dose aspirin for primary prevention in most healthy adults, especially those aged 60 or older. This change is primarily because the risk of major internal hemorrhage often outweighs the minor preventive benefit against a first cardiovascular event. Studies have shown that while aspirin may offer a small reduction in non-fatal heart attacks, it does not significantly reduce the overall incidence of stroke in this group.
Analysis of data from trials in older adults without prior cardiovascular disease found no significant difference in stroke rates between those taking aspirin and those taking a placebo. However, the same analysis revealed that the risk of intracranial bleeding, or bleeding inside the skull, was elevated by approximately 38% in the group taking daily low-dose aspirin. This evidence demonstrates a low or even negative net benefit for broad, routine use of aspirin in primary prevention.
While routine use has been discouraged, a small, select group of younger adults aged 40 to 59 who have a high estimated 10-year risk of cardiovascular disease may still be considered. For these individuals, a healthcare provider may weigh the individual’s specific risk factors against a lower baseline risk of bleeding complications. This decision must be highly individualized and based on a comprehensive assessment of all health data.
Preventing Subsequent Strokes (Secondary Prevention)
Aspirin’s role changes significantly when it is used for secondary prevention, which means preventing a second stroke in someone who has already experienced an ischemic stroke or a transient ischemic attack (TIA). In this context, aspirin is considered a foundational part of the treatment plan because the risk of a recurrent, potentially debilitating or fatal stroke is extremely high. The benefits of antiplatelet therapy in this high-risk population clearly and overwhelmingly outweigh the known bleeding risks.
Aspirin works by permanently blocking a key enzyme in platelets, preventing them from clumping together to form a dangerous clot. This action is crucial in patients with underlying atherosclerotic disease, where plaque has already built up in arteries, creating sites where clots are likely to form. Clinical evidence confirms that aspirin monotherapy can reduce the relative risk of a combined endpoint of stroke, myocardial infarction, and vascular death by about 13% following an initial event.
For maximum early protection following a minor ischemic stroke or TIA, guidelines often recommend a short course of dual antiplatelet therapy. This combines aspirin with another antiplatelet drug for a period of up to 21 days. This combination offers greater initial protection against recurrence, capitalizing on the high-risk window immediately following the first event.
In the long term, low-dose aspirin, typically in the range of 75 to 100 milligrams per day, is generally recommended for ongoing secondary prevention. This dosage range provides effective antiplatelet action while minimizing the dose-dependent risk of serious gastrointestinal side effects. The established efficacy of aspirin in preventing a repeat stroke makes it a highly effective and widely utilized medication.
Major Risks and Required Consultation
Despite its effectiveness in specific situations, aspirin is a medication with real and significant risks that must be understood before use. The primary concern is the increased risk of bleeding, which is a direct consequence of its blood-thinning mechanism. This risk is present regardless of whether the aspirin is used for primary or secondary prevention.
The most common serious adverse effect is gastrointestinal bleeding, which can manifest as stomach ulcers or intestinal hemorrhage. Aspirin irritates the stomach lining and inhibits the platelet function necessary for stopping bleeding from these lesions. The risk of major gastrointestinal bleeding is elevated, sometimes nearly doubling, compared to not taking the drug, and this risk increases with age.
A second, more severe risk is the potential for hemorrhagic stroke, which is bleeding directly into the brain tissue. While aspirin is used to prevent the more common ischemic stroke (clot), its antiplatelet effect can exacerbate a bleed if a vessel ruptures. This is particularly concerning for individuals with uncontrolled high blood pressure, a major risk factor for hemorrhagic stroke.
Because of these serious complications, the decision to begin or discontinue daily aspirin therapy requires a comprehensive risk assessment by a healthcare professional. A doctor must evaluate the individual’s full medical history, current blood pressure, and overall risk profile for both clot-related events and bleeding. Starting daily low-dose aspirin without this professional guidance and personalized risk calculation is strongly discouraged due to the potential for serious harm.