Results Summary

What was the research about?

Heart disease is the leading cause of death in the United States. Doctors recommend that people with heart disease take aspirin to prevent problems, like heart attack or stroke. Questions remain about which dose of aspirin people should take to prevent problems from heart disease while limiting the risk of bleeding related to aspirin.

In this study, the research team compared the safety and effectiveness of low-dose versus high-dose aspirin among patients with heart disease. The team looked at the risks of heart-related health outcomes and the side effects of bleeding.

What were the results?

Patients who took low-dose or high-dose aspirin had a similar risk of:

  • A hospital stay for a heart attack, stroke, or blood transfusion due to a bleeding problem
  • Dying for any reason
  • Having a stent placed in their heart or open heart surgery
  • A hospital stay for a transient ischemic attack, which is a ministroke that lasts a short period of time

Who was in the study?

The study included 15,076 people with heart disease. All received care at one of 40 health centers across the country. Among patients, 80 percent were White, 9 percent were Black, 1 percent were Asian, 1 percent were American Indian or Alaska Native, 1 percent reported more than one race, and 7 percent didn’t report a race; 3 percent were Hispanic. The average age was 68, and 69 percent were men.

What did the research team do?

The research team identified patients for the study by looking at electronic health records in PCORnet®. Patients gave their consent to be in the study. Then, the team assigned patients by chance to take a low dose or a high dose of aspirin. The low dose was 81 milligrams; the high dose was 325 milligrams.

Patients had study visits online or over the phone at the start of the study, one to three weeks later, and every three or six months for up to four years. During study visits, patients answered questions about taking their aspirin dose as recommended and any hospital stays. The research team also reviewed patients’ electronic health records and insurance claims data.

Patients with heart disease helped design the study.

What were the limits of the study?

Most patients in the study were White men. Results may differ for women or people from other racial backgrounds. Among patients assigned to take high-dose aspirin, 42 percent switched to low-dose aspirin during the study. Reasons for switching may have included patient or doctor preference, bruising, or bleeding. The high number of people who switched may have made it hard to detect differences between the doses.

Future research comparing aspirin doses could include more women and people from other racial backgrounds.

How can people use the results?

Patients and their doctors can use these results when considering the dose of aspirin to take to prevent problems from heart disease.

How this project fits under PCORI’s Research Priorities
The PCORnet® Study reported in this results summary was conducted using PCORnet®, the National Patient-Centered Clinical Research Network. PCORnet® is intended to improve the nation’s capacity to conduct health research, particularly comparative effectiveness research (CER), efficiently by creating a large, highly representative network for conducting clinical outcomes research. PCORnet® has been developed with funding from the Patient-Centered Outcomes Research Institute® (PCORI®).

Final Research Report

This project's final research report is expected to be available by March 2024.

More to Explore...

Results of this Study Presented at ACC.21, Published in NEJM

People with cardiovascular disease who took aspirin to lower their chances of having a heart attack or stroke experienced similar health benefits, including reduced death and hospitalization, whether they took a high or low dose of the medication, according to findings from this study released in May 2021.


Summary of Results
English | Español (pdf)
(Credit: DCRI)

The results were presented at ACC.21, the American College of Cardiology’s 70th Annual Scientific Session, and simultaneously published in the New England Journal of Medicine.

This study is the largest aspirin dosing trial conducted in routine care and clinical settings, and the first randomized controlled trial conducted using PCORnet®, the National Patient-Centered Clinical Research Network. Learn more here and through the Summary of Results (right).


Which Aspirin Dose Is Best to Protect Patients with Heart Disease? Our First PCORnet Study
In this blog post, former PCORI Executive Director Joe Selby, MD, MPH, discusses the Board of Governors' approval of funding for this study and some of the key aspects of its design and goals.

Study Website

ADAPTABLE: The Aspirin Study
Duke Clinical Research Institute


ADAPTABLE Study Different by Design
Study co-investigator Adrian F. Hernandez, MD, MHS, FAHA, discusses how this study is uniquely designed in comparison with more traditional trials, and how it aims to achieve its goals in an efficient, effective and patient-centered manner.

Journal Citations

Related Journal Citations

Peer-Review Summary

The Peer-Review Summary for this project will be posted here soon.

Project Information

William Schuyler Jones, MD*
Duke University
Aspirin Dosing: A Patient-Centric Trial Assessing Benefits and Long-term Effectiveness (ADAPTABLE)

Key Dates

May 2015
December 2022

Study Registration Information

*Matthew Roe, MD, MHS was the original Principal Investigator on the project.


Has Results
Health Conditions Health Conditions These are the broad terms we use to categorize our funded research studies; specific diseases or conditions are included within the appropriate larger category. Note: not all of our funded projects focus on a single disease or condition; some touch on multiple diseases or conditions, research methods, or broader health system interventions. Such projects won’t be listed by a primary disease/condition and so won’t appear if you use this filter tool to find them. View Glossary
Populations Populations PCORI is interested in research that seeks to better understand how different clinical and health system options work for different people. These populations are frequently studied in our portfolio or identified as being of interest by our stakeholders. View Glossary
Intervention Strategy Intervention Strategies PCORI funds comparative clinical effectiveness research (CER) studies that compare two or more options or approaches to health care, or that compare different ways of delivering or receiving care. View Glossary
State State The state where the project originates, or where the primary institution or organization is located. View Glossary
Last updated: August 14, 2023