SCANDAL IN MEDICINE: The Aspirin Hemorrhagic Stroke Problem: 21% Reduction in Risk of Death From Any Cancer, 62% Reduction in Preeclampsia

Some studies used the wrong dose, measured the wrong outcome. The 38% relative risk shrinks to a tiny 0.3% absolute risk. I have ordered aluminum-free aspirin (St. Joseph, not Bayer).

Every year, tens of millions of Americans swallow a small yellow or orange tablet: low-dose aspirin. Some take it at a doctor’s recommendation; others, hoping to prevent cardiovascular events. Increasingly, however, patients are advised to stop aspirin based on recent guidelines stating that, for adults 60 and older without established cardiovascular disease, the bleeding risks - in particular, hemorrhagic stroke - outweigh the benefits.¹

Here’s a recent comment on X by a doctor who seem certain that anti-ageologist researcher David Sinclair is doing harm to himself with 81 mg of aspirin per day. The situation, it would seem, is dire for poor David!

Yet this narrative—that even “baby aspirin” significantly increases hemorrhagic stroke risk—is built on studies with methodological limitations that deserve far greater scrutiny than typically received. The risk may be genuine, but it is tiny, and it is located in a particular age group. The certainty with which guidelines are generalized is grossly overstated. Here’s the breakdown, exclusive to Popular Rationalism.

The Dose and Formulation Problem

The widely cited estimate of aspirin-related hemorrhagic stroke risk originates from a 1998 meta-analysis by He et al., pooling 16 trials with a mean aspirin dose of approximately 273 mg per day — over three times the common U.S. preventive dose of 81 mg.² Applying these findings to 81 mg assumes a flat dose-response relationship for bleeding that is neither well-characterized nor necessarily accurate.^3,4

The modern landmark trials — ASPREE, ARRIVE, and ASCEND — each used 100 mg enteric-coated aspirin, further complicating generalization. Enteric coatings alter absorption kinetics and cause variability in platelet inhibition compared to immediate-release formulations.^5,6 Direct evidence for 81 mg immediate-release aspirin specifically remains limited, and extrapolation from these trials to routine clinical practice carries real uncertainty in both directions.

ASPREE: Miscalibration and Misinterpretation

ASPREE is the cornerstone evidence cited in current guidelines. It randomized 19,114 healthy older adults aged 70 and over to 100 mg enteric-coated aspirin or placebo, observing a statistically significant 38% relative increase in intracranial bleeding over 4.7 years.^7,8 Several design features fundamentally distort this risk-benefit picture.

Structural asymmetry. ASPREE anticipated a cardiovascular event rate of 22.4 events per 1,000 person-years and observed roughly half that — reflecting an unusually healthy enrolled population.⁷ This asymmetrically suppressed aspirin’s potential cardiovascular benefit signal while leaving the bleeding risk signal unchanged, artificially inflating the apparent harm-to-benefit ratio.

Population relevance. ASPREE enrolled individuals explicitly free of hypertension, diabetes, and other major risk factors that characterize most actual aspirin users. Generalizing these findings to higher-risk primary prevention populations is not justified by the study design.

Endpoint bundling. Intracranial bleeding in ASPREE was a composite of spontaneous hemorrhagic stroke, traumatic subdural hematoma, extradural hematoma, and subarachnoid hemorrhage.⁸ When disaggregated, the statistically significant finding for hemorrhagic stroke alone disappears. The observed signal primarily reflects trauma-related bleeds — particularly subdural hematomas from falls — rather than spontaneous intracerebral hemorrhages directly caused by aspirin’s antiplatelet mechanism.

Generalizability. ASPREE’s cohort was 91.3% White and 87% Australian.⁷ Stroke epidemiology differs significantly across racial and geographic populations,⁹ⁿ¹⁰ and applying ASPREE results broadly disregards these differences.

Cerebral Amyloid Angiopathy: The Missing Effect Modifier

Cerebral amyloid angiopathy (CAA), characterized by amyloid-beta deposition in cerebral vessel walls, is the leading driver of spontaneous lobar hemorrhagic stroke in older adults.¹¹ Its prevalence rises sharply after age 65 and is particularly elevated in individuals with Alzheimer’s pathology.¹²ⁿ¹³

No aspirin trial — including ASPREE — screened participants for CAA or stratified hemorrhagic outcomes by CAA status. This is not a minor gap. CAA functions as an effect modifier, not a confounder: it doesn’t distort the comparison between treatment arms, but it determines how large aspirin’s bleeding effect is in any given individual. In a patient with structurally compromised amyloid-infiltrated vessels, antiplatelet therapy may meaningfully lower the hemorrhage threshold. In a patient with intact vessels and no CAA burden, the same dose may carry negligible additional risk. The population-average estimate from trials blends these two groups without characterizing the split — meaning the 38% relative increase may substantially overstate risk for CAA-negative individuals while understating it for those with significant amyloid burden.

Confounding by Indication in Observational Data

Observational studies — notably the Cardiovascular Health Study — report alarming associations between aspirin use and hemorrhagic stroke.¹⁴ These suffer from confounding by indication in its most transparent form: patients prescribed aspirin typically have higher baseline cardiovascular and cerebrovascular risk, elevating both ischemic and hemorrhagic stroke rates independently of aspirin. A particularly revealing internal contradiction: the CHS found aspirin associated with increased ischemic stroke in women, a finding directly contrary to aspirin’s antiplatelet mechanism. When an observational study produces results that contradict the known pharmacology of the drug being studied, the most parsimonious explanation is residual confounding. The authors acknowledged this. The literature that cites their hemorrhagic findings generally does not.

Detection and Classification Issues in Earlier Trials

Many trials included in foundational meta-analyses were conducted before widespread CT imaging, creating potential misclassification bias. Aspirin-treated ischemic strokes are more likely to show hemorrhagic transformation on imaging, potentially inflating observed hemorrhagic stroke rates in treatment arms relative to placebo.¹⁵ Modern trials with systematic neuroimaging reduce but do not eliminate this problem — the boundary between hemorrhagic transformation of ischemic stroke and primary intracerebral hemorrhage remains genuinely ambiguous in a non-trivial fraction of cases. This concern is most material for the pre-CT era literature and legacy meta-analyses built from it; it is a minor caveat for ASPREE specifically.

Absolute Versus Relative Risk

The commonly cited “38% relative increase” in intracranial bleeding from ASPREE corresponds to an absolute risk difference of 0.3 percentage points — from 0.8% in the placebo group to 1.1% in the aspirin group — over 4.7 years.⁸ This translates to approximately 3 additional bleeds per 1,000 treated individuals over that period. The number needed to harm is approximately 1,667 patient-years. Presenting the relative figure without this absolute context systematically distorts clinical decision-making and patient communication in ways that have been well-documented in the statistical communication literature.

Methodological Limits Are Lost in Guidelines

The 2022 USPSTF recommendation against initiating aspirin in adults over 60 is heavily shaped by ASPREE, ARRIVE, and ASCEND — three trials each carrying meaningful population or methodological limitations.¹ⁿ¹⁶ ARRIVE enrolled participants at lower cardiovascular risk than intended; ASCEND studied diabetic patients, whose distinct platelet biology may not generalize to the broader population. The guideline conclusions are directionally defensible as population heuristics. The confidence with which they are stated, and the populations to which they have been applied, exceed what the underlying evidence can sustain.

Unexamined Variables: Polypharmacy, Anticoagulants, SSRIs, and NSAIDs

Hypertension is the dominant modifiable driver of hemorrhagic stroke.¹⁷ Trials adjust for baseline blood pressure but rarely track antihypertensive changes over follow-up. In elderly populations followed for four to five years, medication regimens shift frequently. Whether differential antihypertensive adjustments occurred across treatment arms in any major trial is an unexamined variable in each of them.

More consequential is the polypharmacy problem — one of the most underappreciated sources of confounding in the entire aspirin literature.

The anticoagulant interaction is the clearest case. The RE-LY trial subanalysis of intracranial hemorrhage identified four independent predictors across 18,113 anticoagulated patients: warfarin assignment, prior stroke or TIA, age, and concomitant aspirin use (RR 1.6, p=0.01). The authors described aspirin as the most important modifiable independent predictor of ICH in that cohort — ahead of age and prior stroke.¹⁸ The ARISTOTLE trial found that 37.9% of patients who experienced intracranial hemorrhage were on aspirin at baseline, that concomitant aspirin independently predicted ICH, and — critically — that only half of those aspirin users had a formal current indication for it.¹⁹ They were taking it because someone had started it years earlier and the prescription had never been revisited.

This matters enormously for interpreting the primary prevention literature. Atrial fibrillation affects roughly 10% of adults over 70 — the exact demographic that dominates aspirin hemorrhage trials. Many of those individuals are simultaneously on anticoagulants and aspirin, often without a clear current indication for the latter. When an observational study records a hemorrhagic stroke in an “aspirin user,” it cannot tell you whether that person was also on warfarin or a DOAC. The older observational literature — including the Cardiovascular Health Study with its fourfold risk estimate — did not adequately characterize co-anticoagulant use.

SSRIs are the overlooked cofactor. They are among the most widely prescribed drug classes in the elderly and carry meaningful antiplatelet activity through serotonin depletion in thrombocytes. The combination of SSRIs with aspirin is associated with elevated intracranial hemorrhage risk beyond either agent alone through two separate and simultaneous mechanisms of platelet inhibition.²⁰ NSAIDs compound this further: available over the counter, chronically underreported in medication histories, they independently elevate bleeding risk while also partially antagonizing aspirin’s antiplatelet effect through competitive COX-1 binding.

ASPREE excluded anticoagulant users at enrollment — controlling for the most obvious source of combination-drug inflation. But it followed participants for 4.7 years, during which a meaningful number would have developed atrial fibrillation or thromboembolic disease requiring anticoagulation. Whether those new anticoagulant initiations were distributed equally across aspirin and placebo arms, and whether newly anticoagulated aspirin-arm participants accounted for a disproportionate share of the intracranial bleeding events driving the composite finding, has not been published. The ASPREE dataset contains the data to answer this question.

The policy implication is precise. “Stop primary prevention aspirin in the elderly” and “stop aspirin when starting anticoagulation, and systematically review aspirin co-prescriptions in patients over 70” are different clinical recommendations targeting different mechanisms with different expected magnitudes of benefit. The evidence arguably supports the second more directly than the first. The current guideline language collapses them.

The honest summary: 81 mg aspirin probably carries some real but tiny (0.3% absolute) hemorrhagic risk in structurally vulnerable elderly patients, particularly those with significant CAA burden. But a meaningful fraction of what the literature records as aspirin-attributable intracranial hemorrhage is almost certainly aspirin acting as an amplifier in polypharmacy combinations — with anticoagulants, SSRIs, and NSAIDs — that the trials were never designed to characterize. The culprit, in many cases, is not one drug. It is the pile of drugs, and nobody is auditing the pile.

The Real Scandal: Cancer Prevention and Prevention of Death from Cancer

There is a number that does not appear in the 2022 USPSTF recommendation against aspirin. It is not buried in an appendix. It is simply absent. That number is how many cancer deaths aspirin prevents. And it’s not small.

The guidelines that told tens of millions of Americans to stop taking their daily aspirin were built around a single benefit: the reduction in heart attacks and ischemic strokes. Against that benefit, the task force weighed the bleeding risks discussed at length in this article. The math was close, and in older adults the bleeding risks edged out. Guidelines issued. Prescriptions stopped. Pills went in the trash.

What was not weighed is this: aspirin reduces the risk of dying from cancer.

Not colorectal cancer specifically, though that is the strongest signal. All cancer. A pooled analysis of eight randomized controlled trials — 25,570 participants — found that daily aspirin use was associated with a 21% lower risk of death from any cancer, with the benefit only emerging after five years of use and the absolute reduction in 20-year cancer mortality reaching approximately 7% in some analyses.²¹ For every 1,000 people aged 60 who take aspirin for ten years, approximately 16 will avoid a cancer death they would otherwise have suffered — against roughly two deaths from serious bleeding over the same period.²² That is an 8-to-1 ratio on mortality alone, before counting prevented heart attacks and strokes. And the attribution of the 2 deaths to aspirin is very much in question.

Intellectual honesty requires acknowledging the counter-finding. ASPREE found higher all-cause cancer mortality in its aspirin arm over 4.7 years (HR 1.31, 95% CI 1.10–1.56).²³ This cannot be dismissed. The most plausible explanation is that 4.7 years is far too short for the protective effect to emerge — the Rothwell meta-analysis shows the benefit only becoming measurable after five years and strengthening thereafter.²¹ What ASPREE may be capturing is a short-term detection artifact: aspirin-induced GI bleeding prompting endoscopic workups that find cancers already present, but unstaged. That means many were potentially self-resolving, distorting the mortality signal. The discordance between short-term and long-term cancer data is genuine scientific uncertainty, and it should be visible to clinicians and patients making decisions, not resolved by omission in either direction.

For colorectal cancer specifically, a pooled analysis of five randomized prevention trials found a 24% reduction in colorectal cancer incidence and a 35% reduction in CRC mortality after an 8–10 year latency.²⁴ The protective effect is documented across more than 150,000 colorectal cancer cases in observational studies, with approximately 30% risk reduction for regular aspirin users.²⁵ An important precision: the evidence for CRC incidence reduction is clearest at doses of 300 mg and above. For low-dose aspirin at 75–100 mg, observational data suggest a smaller incidence reduction of approximately 10–13%, with the mortality benefit more consistent across doses.²⁵ⁿ²⁶ The “20–40% reduction” figure that appears widely in the literature reflects the full dose range; for 81 mg specifically, the incidence estimate belongs at the lower end, with greater confidence in the mortality endpoint.

In 2016, the USPSTF issued a Grade B recommendation endorsing low-dose aspirin for the joint prevention of cardiovascular disease and colorectal cancer in adults aged 50–59 with ≥10% 10-year cardiovascular risk.²⁷ In 2022, the same body reversed the CRC recommendation entirely, finding the evidence for low-dose aspirin on CRC outcomes “unclear” in randomized trial analyses and “highly variable by length of follow-up.”¹ Six years of formal endorsement of aspirin as a cancer-prevention tool, withdrawn quietly in the same document that tightened the cardiovascular restrictions.

Why does the cancer benefit matter structurally? Because aspirin’s mechanism for preventing cancer is almost entirely separate from its mechanism for causing bleeding. Aspirin inhibits COX-2, which drives chronic inflammation — one of the most important promoters of tumor development across multiple cancer types. This anti-inflammatory effect has nothing to do with platelet inhibition, which is the mechanism behind both aspirin’s cardiovascular benefit and its hemorrhagic risk. In principle, cancer prevention and bleeding risk should be weighed independently. In practice, those two conversations have never been formally joined in a single guideline document, and the cancer side of the ledger has been evaluated under evidentiary standards — short follow-up, cardiovascular trial populations, no cancer-specific primary endpoints — that systematically underestimate a benefit requiring a decade to fully develop.

This creates a timing problem that has received almost no policy attention. A person who starts aspirin at 55 and stops at 68 — because their physician acted on the 2022 guidelines — may have absorbed a decade of bleeding risk while collecting none of the cancer protection quietly accumulating over that period. The biology does not observe guideline revision dates. But tomorrow is another new day.

The cancer-protective effect extends beyond the colon. Regular aspirin use is associated with approximately 35–40% reduced incidence of esophageal adenocarcinoma and gastric cancer, through the same COX-2 and prostaglandin E2 mechanisms — a consistency of direction across multiple large observational meta-analyses that is difficult to attribute to chance.²⁵ For breast, lung, and prostate cancer, the evidence is more heterogeneous, drawn primarily from observational cohorts, and should be treated as hypothesis-generating rather than established.

The dementia question is not settled. Chronic neuroinflammation driven by COX-2 activity is implicated in Alzheimer’s pathology, and aspirin’s anti-inflammatory properties could in principle slow neurodegeneration. Observational data have shown associations between long-term aspirin use and reduced dementia incidence. ASPREE found no cognitive benefit over 4.7 years — but neurodegeneration prevention almost certainly operates on a decades-long timescale, making ASPREE’s follow-up duration inadequate as a test of this hypothesis. The question deserves more research attention than it currently receives.

Beyond cancer and neurology, there are benefits that the standard risk-benefit framing ignores because they apply to populations entirely absent from the conversation.

Preeclampsia is a hypertensive complication of pregnancy that kills mothers and babies and is a leading cause of preterm birth worldwide. Low-dose aspirin started before 16 weeks of gestation in high-risk women reduces preterm preeclampsia by approximately 62% in the best-designed randomized trial.²⁸ The mechanism is well-characterized: aspirin preferentially acetylates maternal platelet COX-1 in the pre-systemic portal circulation while preserving prostacyclin production in the vascular endothelium, restoring the prostacyclin/thromboxane balance disrupted in preeclampsia. The number needed to treat is between 30 and 50 across meta-analyses²⁹ — an exceptionally powerful effect for a preventive intervention at any price, let alone $4 a bottle. This indication is recommended without controversy by virtually every maternal health guideline in the world. It does not appear in cardiovascular risk-benefit discussions because it involves pregnant women in their twenties and thirties. The drug is the same. The conversation is siloed.

Aspirin also meaningfully reduces VTE recurrence. The WARFASA and ASPIRE trials found that aspirin reduced recurrence of deep vein thrombosis and pulmonary embolism by 30–42% compared to placebo in patients who had completed anticoagulation.³⁰ⁿ³¹ For patients who cannot tolerate indefinite anticoagulation, this is a clinically significant option at substantially lower bleeding cost.

Evidence also exists for migraine prevention (second-line in some guidelines, through platelet and prostaglandin mechanisms) and for potential protective effects in early age-related macular degeneration, though the AMD data are genuinely mixed and should not drive prescribing in either direction.

None of this is an argument that aspirin is safe for everyone, that bleeding concerns are invented, or that guidelines are worthless. None of those conclusions follows from the evidence.

The decision about whether any individual should take low-dose aspirin depends on age, cardiovascular risk profile, cancer risk, fall exposure, concurrent medications, plans for pregnancy, and — critically — how long they have already been taking aspirin and whether stopping now means abandoning protective effects not yet fully materialized. For a 55-year-old with moderate cardiovascular risk, no bleeding history, and a family history of colorectal cancer, the calculation looks very different from the USPSTF framing. The cancer benefit alone — 16 deaths prevented per thousand over ten years, against two deaths from bleeding — may justify continuation independently of cardiovascular considerations. For a 78-year-old who falls frequently, is newly started on an anticoagulant, and has no cancer risk factors, it may runs the other way. This would be risk-stratified consideration, not the patronizing “So you want to die from hemorrhagic stroke?”

Population-level guidelines are necessary. They are a starting point for a conversation with a physician, not a substitute for it. A clinician who weighs only cardiovascular events against hemorrhage is working with an incomplete ledger. The most important thing any reader of this article can do is walk into that conversation knowing the ledger has more columns than the standard framing reveals.

Aspirin has been in continuous use for more than a century. At $4 for a bottle of 300 tablets, it remains among the most cost-effective pharmacological interventions ever studied. The evidence for its benefits — plural, across multiple disease categories, operating through multiple mechanisms — is not hidden. It is scattered across literatures that rarely talk to each other, evaluated in a policy environment that has never been asked to synthesize them into a single honest accounting. That accounting is overdue.

Individual Health Decision-Making

Low-dose aspirin’s risk-benefit ratio is highly individual. Patients at higher cardiovascular risk or lower bleeding risk — younger age, good blood pressure control, low fall risk — may still derive clear net benefit. Conversely, low-risk elderly patients, especially those at high fall risk, with unmanaged hypertension, or on concurrent anticoagulants, may face net harm. Guidelines are useful population heuristics but are not substitutes for patient-specific risk assessment. The question a clinician should be asking is not “what does the guideline say” but “what does this patient’s complete risk profile — cardiovascular, oncological, obstetric, pharmacological — actually look like, and how long have they already been on aspirin?”

Conclusion: Risk Stratified Humility, Not Certainty

Randomized evidence shows a modest increase in total intracranial bleeding with low-dose aspirin, primarily driven by trauma-associated events such as subdural hematomas in fall-prone elderly populations. Evidence for spontaneous hemorrhagic stroke specifically remains inconsistent, non-significant when isolated from composite outcomes, and limited by methodological gaps including population selection, endpoint bundling, dose extrapolation, and uncharacterized biological modifiers such as cerebral amyloid angiopathy. Direct evidence for 81 mg immediate-release aspirin remains sparse. Against these harms sits a cancer mortality benefit — 16 deaths prevented per 1,000 over ten years — that was not incorporated into the risk-benefit calculation that changed a generation of clinical practice. Guidelines should reflect calibrated humility: acknowledging data gaps, distinguishing populations, and urging personalized clinical decisions over population-level certainties applied as if they were individual verdicts.

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