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

View this project's final research report.

Journal Citations

Related Journal Citations

Peer-Review Summary

Peer review of PCORI-funded research helps make sure the report presents complete, balanced, and useful information about the research. It also assesses how the project addressed PCORI’s Methodology Standards. During peer review, experts read a draft report of the research and provide comments about the report. These experts may include a scientist focused on the research topic, a specialist in research methods, a patient or caregiver, and a healthcare professional. These reviewers cannot have conflicts of interest with the study. 

The peer reviewers point out where the draft report may need revision. For example, they may suggest ways to improve descriptions of the conduct of the study or to clarify the connection between results and conclusions. Sometimes, awardees revise their draft reports twice or more to address all of the reviewers’ comments.   

Peer reviewers commented and the researchers made changes or provided responses. Those comments and responses included the following: 

  • Reviewers expressed concern about the lack of diversity among participants in this large and complex pragmatic study and asked the researchers to consider how to improve on this in the future. The researchers acknowledged that the lack of participant diversity affected the generalizability of the study but noted that this lack of diversity was often present in clinical research because of factors such as patient interest and historical mistrust. 
  • Reviewers asked for additional missing details to be added to the report regarding the statistical analysis plan, including handling of missing data, the size of the interaction effect in subgroup analyses and information about sensitivity and per-protocol analyses. The researchers expanded their methods section to incorporate this information so that it matched the information provided in the results section. 
  • Reviewers asked for clarification about the planned subgroup analyses conducted in this study because very little was included about the planned analyses in the methods section. The researchers provided more information about the planned subgroups in the methods section to mirror the results section describing subgroup effects. The researchers also noted that they were able to expand the diversity of participants by allowing for participation without using the online patient portal. The researchers expressed concern that without such expansion in recruitment, the patient sample would have been healthier with lower changes of death or hospitalization due to cardiovascular disease. 
  • In relation to recruitment, the reviewers noted that in the study evaluation description it was clear that the face-to-face method for participant recruitment was more successful than the use of email or portal communications. The reviewers wondered whether this method would be feasible for other clinical trials given the considerable staff and cost burden. The researchers acknowledged this concern and explained that it has been discussed in multiple forums but there are no definitive strategies to overcome such recruitment problems. 


Conflict of Interest Disclosures

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.


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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
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Last updated: March 14, 2024