Aspirin in Cardiovascular Prevention

An Evidence-Based Review of Efficacy, Safety, Dose–Response, and Patient-Specific Stratification in Primary and 二次予防二次予防とは、すでに心臓発作、脳卒中、またはステント治療を経験した患者に対して、次の発作を防ぐために治療を行うことです。.

Publisher	Curing Heart Disease, LLC — curingheartdisease.com
Author	Peter Megdal, PhD
Document type	Educational evidence review (clinician- and informed-reader-facing)
Version	2.2 — final (publication-ready)
Release date	June 23, 2026
Suggested review date	June 2028, or upon revision of USPSTF / ACC-AHA アスピリンAspirin makes blood platelets less sticky, so clots are less likely to form. guidance
Evidence basis	Primary peer-reviewed trials, individual-participant meta-analyses, and guideline statements published in peer-reviewed journals (JAMA, Lancet, NEJM, Circulation). Guideline anchors: USPSTF 2022; ACC/AHA 一次予防一次予防とは、これまでに心臓発作や脳卒中を起こしたことのない人に対して治療を行い、最初の発作を防ぐことです。. 2019; AHA/ACC Chronic Coronary Disease 2023; ACC/AHA Acute Coronary Syndromes急性冠症候群（ACS）は、プラークの突然の破綻やびらんによって引き起こされる、不安定狭心症から完全な心筋梗塞に至るまで、心臓への血流が急激に低下する状態全般を指す包括的な用語です。. 2025.
Disclosures	No commercial sponsorship. No 業界資金Financial sponsorship of scientific research by commercial entities with a stake in the outcome; studies funded by industry have been shown to be more likely to report results favorable to the sponsor's product, introducing systematic bias into health evidence.. Author reports no relevant financial conflicts of interest.

 

Key safety framing — read first •    The benefit–risk balanceBenefit–risk balance refers to the quantitative comparison of the absolute reduction in harmful events a treatment prevents against the absolute increase in harmful events it causes; for aspirin, this balance is highly favorable in secondary prevention (where event rates are high) but close to neutral or unfavorable in primary prevention (where event rates are low). of aspirin differs fundamentally between secondary prevention (people who already have established 心血管疾患心血管疾患とは、心臓発作、脳卒中、下肢の動脈閉塞など、心臓や血管に関する問題の総称です。.) and primary prevention (people who do not). Conclusions in one setting do not transfer to the other. •    For primary prevention, current U.S. Preventive Services Task Force guidance recommends an individualized decision only for adults aged 40–59 with a 10年間の心血管疾患リスク10年間の心血管疾患リスクとは、年齢、性別、血圧、コレステロール、糖尿病の有無、喫煙状況を考慮した検証済みの予測式を用いて推算される、今後10年以内に心筋梗塞や脳卒中などの重大な心血管イベントを発症する確率（パーセンテージで表される）であり、現在のガイドラインでは、一次予防におけるアスピリンの検討対象は成人… of 10% or higher who are not at increased bleeding risk, and recommends against initiating aspirin in adults aged 60 or older. •    “Do not initiate for primary prevention” is not the same as “stop aspirin” or “never use aspirin.” People taking aspirin for established disease should not discontinue it based on primary-prevention data. •    This document is educational and does not constitute individual medical advice. Any decision to start, change, or stop aspirin should be made with a qualified clinician, who can weigh personal ischemic and bleeding risk.

目次

1. Introduction and the primary–secondary prevention paradigm…………………………………………. 3
2. Pharmacology and mechanism of action……………………………………………………………………….. 3
3. Dose–response and dosing frequency………………………………………………………………………….. 4
4. Body weight and mass-based dosing……………………………………………………………………………. 5
5. Patient-specific considerations……………………………………………………………………………………… 6
6. Advanced risk stratification: coronary 動脈動脈は、心臓から全身へ血液を送り出す血管です。. calcium………………………………………………………. 7
7. 家族の歴史Family history means whether your close relatives developed heart disease, and how young they were when it happened. of premature coronary disease………………………………………………………………… 7
8. Complementary and alternative preventive strategies…………………………………………………….. 8
9. Quantitative benefit and harm………………………………………………………………………………………. 8
10. Summary of recommendations by population………………………………………………………………. 9
11. Synthesis: key questions………………………………………………………………………………………….. 10
12. Plain-language summary………………………………………………………………………………………….. 11
13. Limitations and evidence quality……………………………………………………………………………….. 11
14. Disclaimer………………………………………………………………………………………………………………. 12

References…………………………………………………………………………………………………………………… 13

1. Introduction and the primary–secondary prevention paradigm

The role of acetylsalicylic acid (aspirin) in cardiovascular medicine has narrowed substantially over the past two decades. Aspirin was once recommended broadly as a daily prophylactic for adults seeking to prevent cardiovascular disease; it is now understood to have a narrow therapeutic margin that depends heavily on an individual’s baseline ischemic and bleeding risk. Because aspirin prevents occlusive arterial events through the same antiplatelet mechanism that impairs normal hemostasis, its net value rises and falls with the 絶対リスク絶対リスクとは、何かが自分に起こる実際の確率であり、パーセンテージで表されます。今後10年間の心臓発作の絶対リスクが12パーセントである場合、それはあなたと似た人100人のうち約12人が発作を起こすことを意味します。. of the events it is meant to prevent.^[1,2]

The single most important distinction in interpreting the aspirin evidence is between two populations. 二次予防 applies to people with documented cardiovascular disease—prior 心筋梗塞詳しい項目については心臓発作をご覧ください。., 虚血性脳卒中虚血性脳卒中は、脳の一部への血流が遮断され、脳組織が壊死し始めることで起こります。. or transient ischemic attack, stable or 不安定狭心症不安定狭心症は、安静時に現れたり、以前よりも少ない労力で引き起こされたり、あるいは急激に悪化したりする胸部不快感です。., peripheral arterial disease, or prior 血行再建術血行再建術とは、閉塞または狭窄した冠動脈の血流を回復させるために行われる医療または外科的処置（冠動脈バイパス術や経皮的冠動脈インターベンションなど）であり、根底にあるアテローム性動脈硬化のプロセスではなく、物理的な閉塞に対処するものである。. (percutaneous coronary intervention or coronary artery bypass grafting). These individuals carry a high absolute risk of recurrent thrombotic events, so even a moderate 相対リスク相対リスクは2つのグループを比較するもので、このグループの心臓発作の発生率は、あのグループよりも30パーセント低かった。. reduction produces a large absolute benefit that clearly outweighs bleeding hazard. ^[2]

一次予防 applies to people without clinically evident cardiovascular disease. Their absolute annual event rate is low, so the absolute number of ischemic events prevented is small and is largely offset by a parallel absolute increase in major bleeding, principally gastrointestinal hemorrhageGastrointestinal hemorrhage is bleeding within the digestive tract, most commonly in the stomach or upper intestine; it is the most frequent serious bleeding complication of long-term aspirin use and often tips the benefit–risk balance against aspirin in primary prevention. and intracranial hemorrhage. This asymmetry—similar relative effects but very different absolute effects—is the central reason contemporary guidance has moved away from routine primary-prevention use. ^[2,1]

In the landmark individual-participant メタ分析メタアナリシスは、多数の個別研究の結果を統計的に統合して1つの全体的な推定値を算出します。. of the Antithrombotic Trialists’ (ATT) Collaboration, the proportional reduction in serious vascular events was broadly similar in the two settings, but the absolute effects diverged sharply: about a 0.06% per-year absolute reduction in primary prevention versus an absolute reduction roughly an order of magnitude larger in secondary prevention. ^[2]

Three modern primary-prevention trials reported in 2018 reinforced this picture in a contemporary treatment era. ARRIVE randomized 12,546 patients judged to be at moderate cardiovascular risk (and without 糖尿病糖尿病は、体が十分なインスリンを作らないか、あるいは作られたインスリンに反応しなくなることで、血糖値が常に高すぎる状態になる疾患です。. or high bleeding risk) to 100 mg of aspirin or プラセボプラセボとは、本物の薬が実際にどのような効果をもたらすかを研究者が知るために投与される、偽の治療法（砂糖の錠剤や生理食塩水の注射など）である。.; it found no significant reduction in the primary composite cardiovascular endpoint, with more gastrointestinal bleeding (mostly mild to moderate) and no difference in fatal events. Notably, the observed event rate was far lower than projected (roughly 9% versus an anticipated 17%), so the cohort effectively behaved like a lower-risk population—partly because many participants were already taking スタチンスタチンは、肝臓がコレステロールを作るのに使う酵素の働きを遅らせます。肝臓は血液中からより多くのコレステロールを取り除くことでこれに反応し、そこに真の利益があります。. そして 降圧薬An antihypertensive is any drug used to lower high blood pressure. The article distinguishes antihypertensives — which became widely used from the 1970s onward — from statins, noting that blood-pressure drugs contributed to coronary mortality decline well before statin therapy was available.. ^[16]

ARRIVE’s companions completed the contemporary trio: ASCEND tested aspirin in diabetes and ASPREE in older adults (both detailed in Section 5). Together, these trials are the empirical basis for the shift away from routine primary-prevention aspirin. ^[8,5]

2. Pharmacology and mechanism of action

Aspirin’s antithrombotic effect derives from irreversible inhibition of platelet cyclooxygenase-1 (COX-1). Aspirin acetylates a serine residue (Ser-530) within the COX-1 catalytic channel, sterically blocking アラキドン酸アラキドン酸は、リノール酸から体内で合成される長鎖オメガ6脂肪酸であり、炎症促進性と抗炎症性の両方のシグナル伝達分子であるエイコサノイドの前駆体として機能するため、炎症におけるその役割は、「種子油が炎症を引き起こす」という単純な説が示唆するよりも複雑である。. from reaching the active site and permanently halting synthesis of the downstream prostanoid thromboxane A₂ (TxA₂)Thromboxane A₂ is a short-lived chemical released by activated platelets that amplifies platelet aggregation and causes blood vessels to constrict; aspirin's primary antithrombotic benefit comes from permanently blocking its production in platelets., a potent promoter of platelet activation, aggregation, and vasoconstriction. ^[3,4]

Because 血小板Platelets are small, anucleate cell fragments in the blood whose primary role is to clump together at sites of vascular injury to form a clot and stop bleeding; because they cannot synthesize new protein, aspirin's irreversible inhibition of their clotting enzyme lasts for the platelet's entire 7–10 day lifespan. are anucleate and cannot synthesize new タンパク質タンパク質は、体内の筋肉や組織の構築と修復に使用される栄養素です。., COX-1 blockade persists for the platelet’s entire lifespan of roughly 7–10 days. This durable antiplatelet effect contrasts with aspirin’s brief pharmacokinetic exposure: peak plasma concentration occurs within about 30–40 minutes and the plasma half-life is only about 15–20 minutes owing to rapid esterase hydrolysis to salicylate. Even transient portal and systemic exposure is sufficient to inactivate the circulating platelet pool. ^[3,4]

Vascular 内皮細胞すべての血管の内面を覆う薄い細胞層であり、血管緊張の調節、血液凝固の防止、および動脈壁への物質の通過の制御を行います。また、その機能障害はアテローム性動脈硬化における初期の極めて重要な段階です。., by contrast, are nucleated and can resynthesize cyclooxygenase. They produce prostacyclin (PGI₂)Prostacyclin is a chemical produced by the cells lining blood vessels that opposes platelet aggregation and keeps vessels dilated; unlike platelets, vessel-lining cells can regenerate their enzymes, so low-dose aspirin spares prostacyclin production while still blocking platelet-derived TxA₂., a vasodilator and platelet inhibitor that physiologically opposes TxA₂. Low daily doses (about 75–100 mg) achieve near-complete platelet COX-1 inhibition while relatively sparing endothelial prostacyclin, in part because platelets are exposed to aspirin in the portal circulation before first-pass hepatic metabolism. Higher daily doses progressively suppress endothelial prostacyclin as well, eroding this selectivity without adding antithrombotic benefit. ^[3,4]

This dual influence defines aspirin’s benefit–risk profile. Suppressing platelet aggregation reduces shear-induced arterial 血栓症血栓症とは、血管内で血液が固まって血栓ができることです。. at sites of プラーク破裂Plaque rupture is when the protective cap over a plaque tears open, spilling its contents into the bloodstream., but the same impairment of hemostasis raises the risk of mucosal, gastrointestinal, and intracranial bleeding. ^[2,3]

3. Dose–response and dosing frequency

Pharmacodynamic studies show that platelet TxA₂ synthesis is nearly fully suppressed by daily doses in the 75–100 mg range, and that antiplatelet efficacy reaches a plateau above this range. Higher maintenance doses (for example 162–325 mg) have not shown added antithrombotic benefit in long-term prevention, and they are associated with greater dose-dependent gastrointestinal mucosal injury in pharmacologic and historical studies—though, as noted below, the randomized ADAPTABLE comparison did not itself detect a statistically significant difference in major bleeding. Single immediate-release loading doses of 162–325 mg are used in acute coronary syndromes and acute ischemic 脳卒中脳卒中は、脳の一部への血流が詰まりまたは出血によって止まるときに起こります。. to achieve rapid platelet inhibition; this is a distinct, acute indication. ^[3,4,23]

The clearest contemporary evidence on maintenance dose comes from the ADAPTABLE pragmatic trial, which randomized 15,076 patients with established atherosclerotic cardiovascular disease to 81 mg or 325 mg of aspirin daily. Over a median 26.2 months, the primary effectiveness outcome (a composite of all-cause death, hospitalization for myocardial infarction, or hospitalization for stroke) did not differ significantly (estimated event rates 7.28% for 81 mg versus 7.51% for 325 mg; ハザード比ハザード比は、2つのグループでイベントが起こる速さを比較するものです。比率が0.75の場合、治療群でのイベント発生率が4分の一減少し、対照群の4分の3であったことを意味します。. 1.02, 95% CI 0.91–1.14), nor did hospitalization for major bleeding (HR 1.18, 95% CI 0.79–1.77). ^[9]

These results should be read as “no significant difference was detected,” not as proof of exact equivalence. ADAPTABLE was open-label and had substantial crossover: roughly 41% of patients assigned to 325 mg switched to 81 mg, while only about 7% switched in the other direction. Such asymmetric crossover biases the comparison toward the null and limits how strongly a true dose difference can be excluded. With that caveat, the trial supports 81 mg daily as the preferred maintenance dose for most patients on the basis of comparable measured outcomes and better tolerability and 固守服薬遵守とは、処方されたとおりに日々、実際に薬を服用することを意味します。.. Contemporary guidance is concordant: the 2023 AHA/ACC Chronic Coronary Disease guideline recommends low-dose aspirin (75–100 mg, commonly 81 mg) as a Class 1 (Level of Evidence A) single-antiplatelet strategy for patients with chronic coronary disease not on oral anticoagulation. ^[9,21]

Consistent with this, the CURRENT-OASIS 7 program in acute coronary syndromes found that continued higher-dose (300–325 mg) aspirin was not superior to lower-dose (75–100 mg) aspirin for major ischemic outcomes and was associated with more minor and gastrointestinal bleeding—reasoning echoed in the 2025 ACC/AHA acute coronary syndromes guideline, which endorses 75–100 mg for maintenance therapy. ^[10,22]

3.1 Dosing frequency and platelet turnover

Dosing interval is constrained by platelet turnover. The marrow releases a fraction of new, uninhibited platelets into the circulation each day, so once-daily dosing is required to maintain steady-state inhibition. Alternate-day dosingスタチンの連日投与ではなく隔日投与とする処方戦略であり、特に半減期の長いスタチンにおいて、LDL低下効果の大部分を維持しつつ、忍容性のない患者の筋症状を軽減する目的で臨床的に用いられる。. leaves “off-day” gaps during which newly formed platelets restore thromboxane capacity. In the Women’s Health Study, 100 mg of aspirin every other day did not significantly reduce the primary composite of major cardiovascular events in initially healthy women over roughly 10 years, although it reduced ischemic stroke. ^[15]

Pharmacodynamic work helps explain that result: 100 mg taken every other day produces less and more variable platelet inhibition than 81 mg taken daily, suggesting the alternate-day regimen may have under-dosed participants on off days. This reduced platelet suppression may partially explain the Women’s Health Study findings, although alternative explanations—lower-than-expected event rates, limited 統計的検出力Statistical power is a study's ability to detect a real effect if one exists. It depends mostly on how many events occur., and trial-design differences—may also contribute. By similar logic, extending the interval further (every third day) is not supported by clinical-endpoint evidence and is not recommended. ^[18,19,23]

Conversely, in conditions with accelerated platelet turnover—such as essential thrombocythemia and some patients with type 2 diabetes—once-daily dosing can leave incomplete inhibition before the next dose. Pharmacodynamic studies indicate that twice-daily low-dose aspirin can restore more consistent thromboxane suppression in these settings than simply increasing the once-daily dose; this remains a specialized strategy rather than general practice. ^[4]

4. Body weight and mass-based dosing

Whether a fixed low dose suits all body sizes is unsettled. In a pooled individual-participant analysis of more than 100,000 participants across primary- and secondary-prevention trials, Rothwell and colleagues reported a dose–weight interaction: low-dose aspirin (75–100 mg) reduced cardiovascular events mainly in people weighing under about 70 kg, with little benefit above that weight, whereas higher doses (≥325 mg) were effective mainly at higher body weight. The analysis also signaled potential harm at the extremes—greater case fatality of a first cardiovascular event in heavier people taking low-dose aspirin, and increased 全因死亡率全死因死亡とは、心疾患に限らず、あらゆる原因による死亡を意味し、研究が測定できる最も広範で、ごまかしが最も効かない結果です。. among people under 50 kg (hazard ratio 1.52, 95% CI 1.04–2.21). ^[11]

These findings are hypothesis-generating, not practice-defining, and have not been confirmed prospectively. In a prespecified analysis of ASPREE in older adults, body weight did not modify aspirin’s cardiovascular effect, and bleeding risk was not lower in heavier individuals. Pharmacodynamic studies in adults without diabetes have likewise found platelet inhibition by 81 mg or 325 mg to be largely independent of body mass. Subsequent analyses have not consistently replicated the body-weight interaction, and no major guideline currently recommends weight-adjusted aspirin dosing; the most reasonable current reading is that weight-tailored dosing is intriguing but not clinically actionable. ^[5,11]

5. Patient-specific considerations

5.1 Age

Bleeding risk rises steeply with age, while the absolute ischemic benefit of primary-prevention aspirin remains modest. The ASPREE trialASPREE was a large randomized trial testing daily low-dose aspirin versus placebo in adults aged 70 and older (65 and older for U.S. minorities) who were free of cardiovascular disease; it found no significant reduction in cardiovascular events and a higher rate of major bleeding and all-cause mortality in the aspirin group, forming a key basis for recommending against aspirin initiation in older… randomized 19,114 community-dwelling adults (largely aged 70 and older) to 100 mg daily or placebo. Aspirin did not prolong disability-free survival (HR 1.01, 95% CI 0.92–1.11) and did not significantly reduce cardiovascular disease (10.7 versus 11.3 events per 1,000 person-years; HR 0.95, 95% CI 0.83–1.08), but it significantly increased major hemorrhage (8.6 versus 6.2 events per 1,000 person-years; HR 1.38, 95% CI 1.18–1.62) and was associated with higher all-cause mortality (HR 1.14, 95% CI 1.01–1.29), largely cancer-related and interpreted cautiously by the investigators. ^[5,6,7]

These data underpin current guidance: in primary prevention, an individualized decision is reasonable only for adults aged 40–59 at sufficiently high cardiovascular risk and low bleeding risk, and initiation is not recommended at age 60 or older. The USPSTF additionally suggests considering discontinuation of primary-prevention aspirin around age 75. None of this applies to secondary prevention. ^[1]

5.2 Biological sex

Earlier sex-specific analyses suggested aspirin’s primary-prevention benefit was driven more by stroke reduction in women and myocardial-infarction reduction in men. Subsequent work indicates much of this apparent difference may reflect body-size and pharmacokinetic factors rather than sex-specific biology, and contemporary guidance does not recommend different aspirin strategies by sex in primary prevention. ^[2,11]

5.3 Diabetes mellitus

People with diabetes are at elevated cardiovascular risk, but they also bleed more. The ASCEND trial randomized 15,480 adults with diabetes and no known cardiovascular disease to 100 mg daily or placebo. Over a mean 7.4 years, aspirin reduced serious vascular events (8.5% versus 9.6%; rate ratio 0.88, 95% CI 0.79–0.97) but increased major bleeding (4.1% versus 3.2%; rate ratio 1.29, 95% CI 1.09–1.52). The absolute benefit (about 1.1%) was closely matched by the absolute bleeding excess (about 0.9%), corresponding to roughly 91 treated to prevent one serious vascular event and roughly 112 treated to cause one major bleed; no subgroup showed benefit clearly exceeding harm. Aspirin in diabetes therefore requires individualized, 意思決定の共有Shared decision-making is a clinical approach in which the physician and patient together weigh the available evidence — including imaging results, risk factors, and personal goals — to reach a management plan that reflects both medical best practice and the individual's values; the 2025 AHA/ACC guidelines specifically invoke it for athletes found to have elevated coronary calcium scores. rather than routine use. ^[8]

5.4 Concomitant risk factors

Active 喫煙喫煙は血管の内壁を傷つけ、血圧を上げ、血液を凝固しやすくし、プラークの成長を早めます。. and uncontrolled 高血圧Hypertension is the medical term for high blood pressure. raise both atherosclerotic risk and bleeding risk (including intracranial hemorrhage). Because 危険因子危険因子とは、高コレステロール粒子、高血圧、喫煙、糖尿病、家族歴など、病気にかかる可能性を高めるものです。. for ischemic events overlap heavily with risk factors for bleeding, raising baseline cardiovascular risk does not automatically tip the balance toward net benefit. Aggressive control of 血圧血圧とは、血液が動脈の壁を押す力ののことです。120/80のように2つの数字で表されます。上の数字は心臓が収縮するときの圧力で、下の数字は弛緩するときの圧力です。. and tobacco use is both a safer and a more effective first priority than initiating aspirin. ^[2,17]

6. Advanced risk stratification: coronary artery calcium

Because population risk equations imperfectly identify who will actually benefit, 冠動脈石灰化スコア（CACスコア）A non-contrast, ECG-gated CT scan that detects and quantifies calcified plaque in the coronary arteries; the resulting Agatston score reflects the extent of coronary calcification and serves as a direct, disease-based measure of atherosclerotic burden rather than a statistical estimate of risk. has been studied as a tool to allocate primary-prevention aspirin to those most likely to gain. In analyses of the 多民族動脈硬化研究（MESA）心血管疾患の既往がない成人の大規模前向きコホート研究であり、冠動脈カルシウム（CAC）スコアリングに関する基礎的データを提供し、CAC負荷と将来の冠動脈イベントとの間の強い段階的関連性を実証し、CACスコアがゼロであることのリスク上の意義を検証した。., restricted to aspirin-naïve adults under 70 not at high bleeding risk, the relationship between the 5-year number-needed-to-treat (NNT₅) and number-needed-to-harm (NNH₅) shifted favorably as CAC rose. Overall the NNT₅ (476) exceeded the NNH₅ (355); for CAC ≥100 the NNT₅ (140) fell below the NNH₅ (518), indicating a modeled net benefit; and for CAC = 0 the NNT₅ (1,190) far exceeded the NNH₅ (567), indicating a modeled net harm. ^[12,13]

These are modeled estimates derived from observational data, not results from randomized allocation of aspirin by CAC. The 2019 ACC/AHA primary-prevention guideline treats CAC as a risk-enhancing tool to refine risk assessment rather than as a validated test for selecting aspirin therapy; no randomized trial has yet shown that allocating aspirin by CAC improves outcomes. The estimates below should therefore inform shared decision-making, not replace it. ^[17,12]

Table 1. CAC-guided modeled estimates of aspirin benefit versus harm in primary prevention (MESAMESA, the Multi-Ethnic Study of Atherosclerosis, followed thousands of adults with no known heart disease, scanning their arteries and tracking outcomes.; aspirin-naïve adults <70 years, not at high bleeding risk). Modeling assumed a 12% relative reduction in CVD events and a 42% relative increase in major bleeding; figures are observational estimates, not randomized evidence. NNT₅/NNH₅ = 5-year 治療必要数NNT（治療必要数）とは、1人が治療から利益を得るために何人がその治療を受けなければならないかを示す数です。. / to harm.

CAC stratum	5-year NNT₅ (prevent 1 CVD event)	5-year NNH₅ (cause 1 major bleed)	Modeled net effect
Overall cohort	476	355	Modeled harm ≥ benefit
CAC = 0	1,190	567	Modeled net harm — avoid
CAC ≥ 100	140	518	Modeled net benefit (no RCT)

CAC therefore offers a more personalized basis for refining risk than scores alone: a score of zero identifies people in whom bleeding risk likely dominates, while a high score identifies subclinical プラーク負荷プラーク負荷とは、単に最も状態の悪い一箇所だけでなく、動脈全体に存在するプラークの総量のことです。. in which aspirin may be biologically justified, provided bleeding risk is low. These remain modeled inferences pending randomized confirmation. An ultrasound-based carotid 歯垢プラークとは、動脈の壁の内側にコレステロール、免疫細胞、瘢痕組織、カルシウムが蓄積したものです。. score has been studied for the same purpose, with the presence of carotid plaque at higher estimated ASCVD risk marking a more favorable balance. ^[20]

7. Family history of premature coronary disease

A family history of 若年性冠動脈疾患Premature coronary artery disease is coronary atherosclerosis that causes a clinically significant event — such as a heart attack or revascularization — before age 55 in men or age 65 in women; events in relatives at these ages are the primary signal used to define high inherited cardiac risk. (a first-degree male relative affected before 55 or female relative before 65) is recognized in the 2019 ACC/AHA primary-prevention guideline as a risk-enhancing factor that can refine risk assessment. It can meaningfully reclassify an individual’s estimated risk upward, and a strong family history may appropriately prompt further assessment—such as CAC testing—to clarify whether preventive intensification is warranted. It is not, however, an established stand-alone indication for primary-prevention aspirin, and it does not reduce aspirin’s bleeding hazard. The appropriate response to a strong family history is intensified guideline-directed prevention—lipid management, blood-pressure control, and lifestyle measures—rather than reflexive aspirin initiation. ^[17,1]

8. Complementary and alternative preventive strategies

In the modern primary-prevention era, several interventions offer a more favorable benefit–risk profile than aspirin. Statin therapy substantially reduces major cardiovascular events without increasing major hemorrhage, and serious adverse effects such as rhabdomyolysisRhabdomyolysis is the rapid breakdown of skeletal muscle tissue that releases cellular contents — including myoglobin — into the bloodstream; a key warning sign is dark tea- or cola-colored urine, and if untreated it can cause acute kidney failure. are rare. Strict blood-pressure control reduces stroke and myocardial infarction without raising bleeding risk—and directly lowers the risk of 脳出血A hemorrhagic stroke is a type of stroke caused by bleeding into or around the brain rather than by a blocked artery; because aspirin impairs clotting, it raises the risk of this complication, which is a key reason its use in low-risk individuals is now discouraged.. Smoking cessation produces large, rapid reductions in cardiovascular risk. ^[17]

These alternatives also reshape the case for aspirin itself. As background statin use and risk-factor control reduce residual ischemic risk, the incremental absolute benefit of adding aspirin in primary prevention shrinks while its bleeding risk persists. For most people without established disease who are already on guideline-directed therapy, adding aspirin offers little net advantage. ^[2,17]

9. Quantitative benefit and harm

The tables below summarize effect estimates from the principal peer-reviewed sources. Relative effects are broadly similar across settings; the decisive difference is in absolute effect, which is governed by baseline risk. All figures are drawn directly from the cited trials and meta-analyses.

Table 2. Aspirin effects by prevention setting and population, from primary peer-reviewed sources. RR = rate/relative ratio; HR = hazard ratio; CI = 信頼区間信頼区間とは、ある研究の結果と統計的に整合する値の範囲のことです。..

Setting / population	Effect (95% CI)	Outcome and absolute effect	ソース
Primary prevention — serious vascular events	RR 0.88 (0.82–0.94)	0.51% vs 0.57% per year; ≈12% proportional reduction	ATT meta-analysis
Primary prevention — major coronary events	RR 0.82 (0.75–0.90)	≈18% proportional reduction	ATT meta-analysis
Primary prevention — stroke (total)	RR 0.95 (0.85–1.06)	No significant effect	ATT meta-analysis
Primary prevention — major extracranial bleeding	RR 1.54 (1.30–1.82)	0.10% vs 0.07% per year; significant increase	ATT meta-analysis
Primary prevention in diabetes — serious vascular events	RR 0.88 (0.79–0.97)	8.5% vs 9.6%; ARR ≈1.1%; NNT ≈91	ASCEND
Primary prevention in diabetes — major bleeding	RR 1.29 (1.09–1.52)	4.1% vs 3.2%; ARI ≈0.9%; NNH ≈112	ASCEND
Primary prevention in older adults — CVD	HR 0.95 (0.83–1.08)	10.7 vs 11.3 / 1,000 py; not significant	ASPREE
Primary prevention in older adults — major hemorrhage	HR 1.38 (1.18–1.62)	8.6 vs 6.2 / 1,000 py; significant increase	ASPREE
Secondary prevention — serious vascular events	≈one-fifth proportional reduction	≈6.7% vs 8.2% per year; large absolute benefit	ATT meta-analysis

Table 3. Maintenance-dose comparison (81 mg vs 325 mg daily) in secondary prevention.

成果	81 mg	325 mg	Effect (95% CI)
Composite: death, MI, or stroke hospitalization	7.28%	7.51%	HR 1.02 (0.91–1.14)
Hospitalization for major bleeding	—	—	HR 1.18 (0.79–1.77)
Switched to the other dose (crossover)	≈7%	≈41%	Asymmetric — biases toward null

Source: ADAPTABLE. The marked asymmetric crossover is the key limitation and is why the trial supports 81 mg as preferred without proving exact dose equivalence. ^[9]

10. Summary of recommendations by population

The table below states, for each population, the action (initiate, continue, or avoid) together with its setting and the supporting guidance. Every row preserves the primary-versus-secondary distinction.

Population	Action	Rationale	Guidance
Established ASCVD / post-MI / post-stroke / post-PCI or CABG (secondary prevention)	Continue (81 mg daily)	High recurrent-event risk; absolute benefit far exceeds bleeding risk	2023 AHA/ACC CCD (Class 1, LOE A); ATT; ADAPTABLE
Primary prevention, age 40–59, 10-yr CVD risk ≥10%, low bleeding risk	Individualize	Small net benefit; depends on personal risk and preference	USPSTF GradeGRADE (Grading of Recommendations, Assessment, Development and Evaluations) is a widely used framework for rating the certainty of evidence behind a clinical finding, classifying it as high, moderate, low, or very low based on factors such as study design, risk of bias, consistency, directness, and precision of results. C
Primary prevention, age ≥60	Do not initiate	No net benefit; bleeding risk dominates	USPSTF Grade D
Primary prevention with elevated bleeding risk (any age)	Do not initiate	Bleeding hazard outweighs any ischemic benefit	USPSTF; ACC/AHA
Primary prevention, CAC = 0	Avoid	Modeled net harm; very low ischemic risk (observational estimate)	MESA modeling
Primary prevention, CAC ≥100, low bleeding risk	Consider	Modeled net benefit (NNT₅ < NNH₅); no randomized confirmation	MESA modeling
Primary prevention in diabetes, no ASCVD	Individualize	Benefit and bleeding excess closely matched	ASCEND; ADA/guidelines

11. Synthesis: key questions

Who benefits most?

People with established cardiovascular disease (secondary prevention). Their high recurrent-event risk means the absolute benefit of low-dose aspirin clearly exceeds bleeding risk. Low-dose aspirin (81 mg daily) is standard long-term therapy for most secondary-prevention patients unless contraindicated or superseded by an alternative antithrombotic strategy—for example, oral anticoagulation for another indication, or a defined dual-antiplatelet course after recent stenting or acute coronary syndrome. ^[2,9,21]

Who benefits least?

Adults without cardiovascular disease who are already on guideline-directed prevention (effective statin therapy, blood-pressure control, non-smoking). Their residual ischemic risk is low, so added aspirin offers little incremental benefit while bleeding risk remains. ^[2,17]

Which populations should generally avoid initiating primary-prevention aspirin?

Adults aged 60 or older; adults of any age at increased bleeding risk; people with CAC of zero; and, on current evidence, those at the low end of body weight in whom harm signals have been raised. ^[1,12,11]

What is the lowest effective maintenance dose?

A daily dose of about 75–81 mg provides near-maximal platelet inhibition and comparable clinical protection to higher doses, with less gastrointestinal and bleeding toxicity. ^[3,9]

Is daily dosing better than alternate-day dosing?

Yes. Daily low-dose aspirin gives more consistent platelet inhibition than alternate-day dosing, because newly formed platelets restore thromboxane capacity during off-day intervals. ^[15,18]

Do doses above ~100 mg add cardiovascular benefit?

No consistent evidence demonstrates superior cardiovascular outcomes with routine maintenance doses above roughly 100 mg, while higher doses are associated with greater gastrointestinal toxicity. Higher single doses remain appropriate only for acute loading in acute coronary syndromes or acute stroke. ^[9,10,22]

What is the overall 2025-and-beyond consensus?

For secondary prevention, low-dose aspirin remains a cornerstone: the 2023 AHA/ACC Chronic Coronary Disease guideline gives low-dose aspirin (75–100 mg) a Class 1 recommendation as single-antiplatelet therapy in patients not on anticoagulation, and the 2025 ACC/AHA acute coronary syndromes guideline likewise endorses 75–100 mg maintenance dosing. For primary prevention, routine use has been abandoned; any decision should be individualized, generally limited to adults 40–59 at ≥10% 10-year risk with low bleeding risk, and is well suited to refinement with imaging-based risk markers such as CAC. ^[1,21,22]

12. Plain-language summary

Aspirin makes platelets—the blood cells that form clots—less able to stick together, which lowers the chance of a clot blocking an artery and causing a 心臓発作心臓発作は、心筋の一部への血流が遮断され、その筋肉が壊死し始めることで起こります。. or stroke. Because platelets cannot repair themselves, one low dose keeps working for about 7–10 days. The same effect makes bleeding harder to stop, which is why aspirin can cause bleeding in the stomach, intestines, or brain.

The key idea is that aspirin’s value depends on whether you already have heart or vascular disease:

• If you have already had a heart attack, stroke, ステントステントとは、狭くなった動脈の内側で広げて開いた状態を保つ、小さな金属製のメッシュ状のチューブのことです。., or bypass (secondary prevention), the chance of another event is high, and daily low-dose aspirin clearly does more good than harm. Do not stop it on your own.
• If you have no history of heart or vascular disease (primary prevention), the benefit is much smaller and is largely cancelled out by bleeding risk. Guidelines advise against starting aspirin at age 60 or older, and only individualized consideration for adults 40–59 at higher risk.

Tools such as a coronary calcium scan can help identify who in the primary-prevention group might still benefit. For preventing a first heart attack or stroke, statins and blood-pressure control generally provide greater and safer protection than aspirin.

Table 4. Plain-language summary of who benefits and who should be cautious.

Aspirin generally helps	Aspirin is usually not advised (for prevention)
Prior heart attack	Starting aspirin at age 60 or older
Prior ischemic stroke or TIA	Increased bleeding risk (ulcers, 抗凝固薬An anticoagulant reduces the blood's ability to clot by interfering with clotting proteins. Warfarin and apixaban are examples., etc.)
Coronary stent or バイパス手術バイパス手術では、体の他の部位から健康な血管を採取し、それを使用して、ひどく閉塞した冠動脈の周囲に血液を迂回させます。.	No heart disease and a coronary カルシウムスコアカルシウムスコア（冠動脈カルシウムスコア）とは、CTスキャンから算出される数値であり、冠動脈内の石灰化したプラークの総量を数値化したものです。スコアがゼロの場合は検出可能な石灰化プラークがないことを示し、より高いスコアはプラークの蓄積が多く、心血管疾患のリスクが高いことを反映しています。. ゼロの
High plaque burden (CAC ≥100) with low bleeding risk	Already well-protected on statin, blood-pressure control, non-smoking

Preferred maintenance dose when aspirin is indicated: 81 mg once daily.

13. Limitations and evidence quality

The primary-prevention estimates rest on trials conducted across different eras and risk profiles; contemporary background therapy (statins, better blood-pressure control) tends to reduce the residual benefit of aspirin relative to older trials. The dose-comparison evidence (ADAPTABLE) is open-label with substantial crossover, so it constrains rather than proves dose equivalence. Weight-based dosing and twice-daily strategies are supported mainly by pharmacodynamic and post-hoc data and have not been validated in dedicated outcome trials. CAC-based allocation rests on observational modeling rather than randomized allocation. These limitations argue for individualized, clinician-guided decisions rather than blanket rules. ^[9,11,12]

14. Disclaimer

This document is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment, nor does it establish a clinician–patient relationship. Individual ischemic and bleeding risks, medications, and comorbidities vary widely. Any decision to start, continue, change, or stop aspirin should be made together with a qualified healthcare professional.

参考文献

1. US Preventive Services Task Force, Davidson KW, Barry MJ, et al. Aspirin Use to Prevent Cardiovascular Disease: US Preventive Services Task Force Recommendation Statement. JAMA. 2022;327(16):1577-1584. doi:10.1001/jama.2022.4983
2. Antithrombotic Trialists’ (ATT) Collaboration, Baigent C, Blackwell L, et al. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised trials. Lancet. 2009;373(9678):1849-1860. doi:10.1016/S0140-6736(09)60503-1
3. Awtry EH, Loscalzo J. Aspirin. Circulation. 2000;101(10):1206-1218. doi:10.1161/01.cir.101.10.1206
4. Patrono C, García Rodríguez LA, Landolfi R, Baigent C. Low-dose aspirin for the prevention of atherothrombosis. N Engl J Med. 2005;353(22):2373-2383. doi:10.1056/NEJMra052717
5. McNeil JJ, Wolfe R, Woods RL, et al. Effect of Aspirin on Cardiovascular Events and Bleeding in the Healthy Elderly. N Engl J Med. 2018;379(16):1509-1518. doi:10.1056/NEJMoa1805819
6. McNeil JJ, Woods RL, Nelson MR, et al. Effect of Aspirin on Disability-free Survival in the Healthy Elderly. N Engl J Med. 2018;379(16):1499-1508. doi:10.1056/NEJMoa1800722
7. McNeil JJ, Nelson MR, Woods RL, et al. Effect of Aspirin on All-Cause Mortality in the Healthy Elderly. N Engl J Med. 2018;379(16):1519-1528. doi:10.1056/NEJMoa1803955
8. ASCEND Study Collaborative Group, Bowman L, Mafham M, et al. Effects of Aspirin for Primary Prevention in Persons with Diabetes Mellitus. N Engl J Med. 2018;379(16):1529-1539. doi:10.1056/NEJMoa1804988
9. Jones WS, Mulder H, Wruck LM, et al. Comparative Effectiveness of Aspirin Dosing in Cardiovascular Disease. N Engl J Med. 2021;384(21):1981-1990. doi:10.1056/NEJMoa2102137
10. CURRENT-OASIS 7 Investigators, Mehta SR, Bassand JP, et al. Dose comparisons of clopidogrel and aspirin in acute coronary syndromes. N Engl J Med. 2010;363(10):930-942. doi:10.1056/NEJMoa0909475
11. Rothwell PM, Cook NR, Gaziano JM, et al. Effects of aspirin on risks of vascular events and cancer according to bodyweight and dose: analysis of individual patient data from randomised trials. Lancet. 2018;392(10145):387-399. doi:10.1016/S0140-6736(18)31133-4
12. Cainzos-Achirica M, Miedema MD, McEvoy JW, et al. Coronary Artery Calcium for Personalized Allocation of Aspirin in Primary Prevention of Cardiovascular Disease in 2019: The MESA Study (Multi-Ethnic Study of Atherosclerosis). Circulation. 2020;141(19):1541-1553. doi:10.1161/CIRCULATIONAHA.119.045010
13. Miedema MD, Duprez DA, Misialek JR, et al. Use of coronary artery calcium testing to guide aspirin utilization for primary prevention: estimates from the multi-ethnic study of atherosclerosis. Circ Cardiovasc Qual Outcomes. 2014;7(3):453-460. doi:10.1161/CIRCOUTCOMES.113.000690
14. Steering Committee of the Physicians’ Health Study Research Group. Final report on the aspirin component of the ongoing Physicians’ Health Study. N Engl J Med. 1989;321(3):129-135. doi:10.1056/NEJM198907203210301
15. Ridker PM, Cook NR, Lee IM, et al. A randomized trial of low-dose aspirin in the primary prevention of cardiovascular disease in women. N Engl J Med. 2005;352(13):1293-1304. doi:10.1056/NEJMoa050613
16. Gaziano JM, Brotons C, Coppolecchia R, et al. Use of aspirin to reduce risk of initial vascular events in patients at moderate risk of cardiovascular disease (ARRIVE): a randomised, double-blind, placebo-controlled trial. Lancet. 2018;392(10152):1036-1046. doi:10.1016/S0140-6736(18)31924-X
17. Arnett DK, Blumenthal RS, Albert MA, et al. 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2019;140(11):e596-e646. doi:10.1161/CIR.0000000000000678
18. Swaim L, Hillman RS. Aspirin administered to women at 100 mg every other day produces less platelet inhibition than aspirin administered at 81 mg per day: implications for interpreting the women’s health study. J Thromb Thrombolysis. 2009;28(1):94-100. doi:10.1007/s11239-008-0262-6
19. Feldman M, Cryer B, Rushin K, Betancourt J. A comparison of every-third-day versus daily low-dose aspirin therapy on serum thromboxane concentrations in healthy men and women. Clin Appl Thromb Hemost. 2001;7(1):53-57. doi:10.1177/107602960100700111
20. Dzaye O, Razavi AC, Dardari ZA, et al. Carotid Ultrasound-Based Plaque Score for the Allocation of Aspirin for the Primary Prevention of Cardiovascular Disease Events: The Multi-Ethnic Study of Atherosclerosis and the Atherosclerosis Risk in Communities Study. J Am Heart Assoc. 2024;13(12):e034718. doi:10.1161/JAHA.123.034718
21. Virani SS, Newby LK, Arnold SV, et al. 2023 AHA/ACC/ACCP/ASPC/NLA/PCNA Guideline for the Management of Patients With Chronic Coronary Disease: A Report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines. Circulation. 2023;148(9):e9-e119. doi:10.1161/CIR.0000000000001168
22. Rao SV, O’Donoghue ML, Ruel M, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2025;151(13):e771-e862. doi:10.1161/CIR.0000000000001309
23. Patrono C. The Multifaceted Clinical Readouts of Platelet Inhibition by Low-Dose Aspirin. J Am Coll Cardiol. 2015;66(1):74-85. doi:10.1016/j.jacc.2015.05.012