Cosmos Study

Low-Dose Aspirin Usage for Primary Prevention of Cardiovascular Disease Has Fallen by More Than Half Since 2018

April 16, 2026

Team A:Kersten Bartelt, RNTed StampGregory Edwards, PhD

Team B:Jeff Trinkl, MDDave Little, MDEric BarkleyJoe Deckert, PhD

Key Findings

The proportion of primary care encounters with low-dose aspirin on the medication list fell by more than half, from a peak of 7.4% in mid-2018 to 3.2% by the end of 2025, among patients without a history that warrants low-dose aspirin for secondary prevention. The decline was observed across all demographic subgroups. Adults aged 80+ still had the highest prevalence at 5.7%.
Aspirin users aged 75 and older had a significantly higher risk of major bleeding: 33% higher for ages 75–79 and 37% higher for ages 80 and above compared to patients with an aspirin allergy. For adults under 75, the difference in bleeding risk between aspirin users and those with an aspirin allergy was not statistically significant.

Low-dose aspirin (typically 81 mg taken daily) was long recommended to help prevent a first heart attack or stroke in adults at elevated cardiovascular risk. Based on earlier trial evidence, the 2016 U.S. Preventive Services Task Force (USPSTF) endorsed daily aspirin for adults aged 50–69 with at least a 10% ten-year risk of cardiovascular disease (CVD) who were not at increased risk for bleeding.¹ However, three large trials published in 2018 (ARRIVE², ASCEND³, and ASPREE⁴) found that the cardiovascular benefits of aspirin for primary prevention were smaller than previously observed and were largely offset by an increased risk of serious bleeding. These findings prompted major guideline revisions: the 2019 ACC/AHA guideline recommended against routine primary-prevention aspirin and limited consideration to select adults aged 40–70 at higher CVD risk,⁵ and the 2022 USPSTF update recommended against initiating aspirin in adults 60 and older altogether.⁶ Despite these shifts, it is unclear how quickly prescribing practices have changed, and while aspirin’s bleeding risk is well-established in clinical trials, less is known about which real-world patient characteristics most strongly predict serious bleeding in primary prevention populations.

For the prescribing trends analysis, we examined 279 million primary care encounters that occurred between 2015 and 2025 among adults aged 40 and older. Patients with conditions that would indicate aspirin use for secondary prevention (such as coronary artery disease, prior stroke, or peripheral artery disease) as well as those for whom aspirin was contraindicated due to allergy or pregnancy were excluded.

The share of visits where low-dose aspirin appeared on the medication list fell from a peak of 7.4% in mid-2018 to 3.2% by the end of 2025, a reduction of more than half. The decline has been steady since 2018, and the downward trend was consistent across all demographic subgroups. Notably, adults aged 80 and older, the group current guidelines most strongly recommend against starting on aspirin, still had the highest prevalence at 5.7% in late 2025, down from a peak of 10.9%.

Figure 1

Quarterly Rate of Low-Dose Aspirin per Primary Care Encounter

Figure 1. Low-dose aspirin prevalence rates among adults aged 40+ without a secondary prevention indication. See interactive web version for additional demographic group breakouts.

For the bleeding risk analysis, we studied 625,742 patients aged 40 and older who received their first prescription for daily low-dose aspirin between 2017 and 2025, excluding those with a prior bleeding diagnosis, secondary prevention indications, or pregnancy. To isolate the effect of aspirin itself on bleeding, we needed a comparison group that was similar in health profile but not taking aspirin. We matched aspirin-prescribed patients with those who had an allergy to aspirin documented, a group unlikely to be using aspirin. Matching was based on demographics, start year, comorbidities, and ulcer medication use.

Aspirin’s association with major bleeding was concentrated in adults 75 and older, consistent with findings from earlier clinical trials.^2,3,4 Patients aged 75–79 who used aspirin had a 33% higher risk of major bleeding compared to same-aged patients with a documented aspirin allergy, and those aged 80 and above had a 37% higher risk. For adults under 75, there was no significant difference in bleeding risk between aspirin users and those with an allergy to aspirin.

Figure 2

Likelihood of a Major Bleeding Event by Low-Dose Aspirin Use

Figure 2. The likelihood of a patient experiencing a major bleeding event on low-dose aspirin compared to those with an aspirin allergy.

These data come from Cosmos, a dataset created in collaboration with a community of Epic health systems representing more than 300 million patient records from 2,000 hospitals and more than 47,000 clinics from all 50 U.S. states, Canada, Lebanon, and Saudi Arabia. This study was completed by two teams that worked independently, each composed of a clinician and research scientist. The two teams came to similar conclusions. Graphics by Brian Olson.

References

Bibbins-Domingo K; US Preventive Services Task Force. Aspirin use for the primary prevention of cardiovascular disease and colorectal cancer: US Preventive Services Task Force recommendation statement. Ann Intern Med. 2016;164(12):836-845. doi:10.7326/M16-0577
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
ASCEND Study Collaborative Group. Effects of aspirin for primary prevention in persons with diabetes mellitus. N Engl J Med. 2018;379(16):1529-1539. doi:10.1056/NEJMoa1804988
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
Arnett DK, Blumenthal RS, Gersh B, 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
Davidson KW, Barry MJ, Mangione CM, 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

Data Definitions

Study period: Trends: 1/1/2015 to 12/31/2025
Bleeding: 2017 to 2025

Study population: inclusion

Both studies:

Aged 40+

Trends study only:

With a face-to-face visit in a primary care department in the study period
With a face-to-face visit in a primary care department in the prior two calendar years

Bleeding study only:

With a prescription for low-dose aspirin or a documented aspirin allergy
Documented legal sex and ZIP code
At least one face-to-face visit in the year prior to the index date
At least one face-to-face visit after the index date

Index date (Bleeding study): Exposures: first order for low-dose aspirin
Controls: date of documented aspirin allergy or 1/1/2017, whichever comes last

Study population: exclusions

Patients with a history of an outcome diagnosis (Bleeding study)
First low-dose aspirin on record is historical/patient reported (Bleeding study)
Aspirin allergy (Trends study)
Pregnancy episode overlapping the quarter or a pregnancy diagnosis within four months before or after the visit (Trends study)
History of:

Ischemic stroke/TIA: any diagnosis with ICD-10-CM code I63*, I65*, I66*, G45*, Z86.73
Prior coronary/cerebrovascular/peripheral revascularization procedures: CPT code 92925-92944, 33510-33536, 35301, 37215-37218, 37220-37235
CAD: any diagnosis with ICD-10-CM code I20*, I21*, I22*, I23*, I24*, I25*
PAD: any diagnosis with ICD-10-CM code I70* or I73.9
Thrombophilia / antiphospholipid syndrome (APS): any diagnosis with ICD-10-CM code D68.61, D68.59
Gastrointestinal ulcers: any diagnosis with ICD-10-CM code K25-K28*
Gastritis and duodenitis: any diagnosis with ICD-10-CM code K29*

Censoring: Last face-to-face visit
Pregnancy

Low-dose aspirin (Trends study)

An outpatient prescription or historical medication with a generic name of “aspirin” and a frequency of “daily,” “every 24 hours,” “nightly,” or unspecified, and either:

Strength of 75 mg, 80 mg, 81 mg, or 100 mg AND dose of 1 (unit ignored) or unspecified
OR Dose between 75 and 100 (units ignored)

Low-dose aspirin (Bleeding study): A prescription with a simple generic name of “aspirin,” a frequency of “daily,” “nightly”, or “every 24 hours”, and a dose ≤ 100 mg, or a dose of 1 tablet or 1 each, and a strength of 81 mg or 100 mg and an outpatient order mode

Face-to-face visit: An encounter of type “Office visit,” “Follow-up,” “Telemedicine,” “Urgent Care,” or “Walk-in”

Primary care department: An encounter in a department with a specialty of “Elder Care Services,” “Family Medicine,” “General Internal Medicine,” “Gerontology,” “Internal Medicine,” “Medical Clinic,” “Preventative Medicine,” or “Primary Care”

Aspirin allergy: An allergy or reaction documented to an allergen containing the text “aspirin”, but not containing any of “aspirin-free,” “aspirin free,” “non-aspirin,” “non aspirin,” “no aspirin,” “no-aspirin,” “w/o aspirin,” “w/out aspirin,” or “without aspirin”

Pregnancy diagnosis: A diagnosis with ICD-10-CM code O*

Major bleeding event: A clinical or billing diagnosis with ICD-10-CM code K25.0, K25.2, K25.4, K25.6, K26.0, K26.2, K26.4, K26.6, K27.0, K27.2, K27.4, K27.6, K28.0, K28.2, K28.4, K28.6, K29.01, K29.21, K29.31, K29.41, K29.51, K29.61, K29.71, K29.81, K29.91, S06.4*-S06.6*, or I60*-I62*