Doctor, I have been diagnosed with COVID-19 infection and will be recovering at home. Should I take an anticoagulant or aspirin to prevent blood clots?

People with mild COVID-19 infections who do not need a hospital stay had a low chance of developing DVT or PE. However, people already on an anticoagulant or aspirin prior to being diagnosed with COVID-19 infection should not stop these drugs without consulting with their doctor.

Study highlights

The risk of developing bad outcomes such as DVT, PE, stroke, heart attack, need for hospital admission or death did not differ for people who received apixaban (at high or low doses) or aspirin compared with those who received placebo.

About 7 more people out of 100 taking apixaban at treatment dose had bleeding events.

Understanding the problem

About 1 in 40 people diagnosed with COVID-19 who is ill enough to need to be admitted to the hospital will develop a DVT or PE. If someone needs to be cared for in the intensive care unit (ICU), the risk of developing a DVT or PE increases to about 1 in 10 people. Having a DVT or PE is a serious complication of COVID-19 infection, because a PE can reduce the ability to get oxygen from the lungs into the blood, which can contribute to death.

Several studies tell us that using higher doses of injectable anticoagulants in people with COVID-19 infections who are admitted to the hospital can help prevent their lung function from getting worse and speed up recovery from the disease. On the other hand, higher doses of anticoagulants did not help people already on a breathing machine (mechanical ventilator) or in the ICU and increased their risk of bleeding.

The study investigators wanted to know if giving oral anticoagulants or aspirin to people with COVID-19 infections who do not need to stay in hospital might protect them from bad events like DVT, PE, stroke, heart attack or requirement for admission to hospital or death.

Who? The study included 657 people aged 40 to 80 years, who had COVID-19 infection mild enough to not require a hospital stay at diagnosis. **It is important to know that vaccines were not widely available during the time frame for this study.

What? The study compared 4 groups: apixaban at treatment dose, apixaban at prevention dose, aspirin, and placebo.

Apixaban at treatment dose

Apixaban at preventative dose



Apixaban 5mg twice a day

Apixaban 2.5mg twice a day

Aspirin 81mg once a day

Placebo: A pill/needle/lotion containing an inactive substance that has no effect on the outcome. Sometimes, it is referred to as a “sugar pill.”

Apixaban, aspirin, or placebo in people who have mild COVID-19 infections not needing to stay in hospital at diagnosis

Outcomes at 45 days

Rate of events with apixaban at treatment dose

Rate of events with apixaban at preventative doseRate of events with aspirin

Rate of events with placebo


Symptomatic DVT, PE, heart attack, stroke, hospital admission for heart or lung issues, or death

1 out of 100 people

1 out of 100 people1 out of 100 people

1 out of 100 people

No effect

Major bleeding

0 out of 100 people

0 out of 100 people0 out of 100 people

0 out of 100 people

No effect

Any bleeding9 out of 100 people7 out of 100 people4 out of 100 people2 out of 100 peopleAbout 7 more people taking apixaban at treatment dose had bleeding compared to people taking placebo

This Evidence Summary is based on the following article:

Connors JM, Brooks MM, Sciurba FC, et al. Effect of Antithrombotic Therapy on Clinical Outcomes in Outpatients With Clinically Stable Symptomatic COVID-19: The ACTIV-4B Randomized Clinical Trial. JAMA. 2021 Oct 11. pii: 2785218. doi: 10.1001/jama.2021.17272. PubMed

Published: Thursday, December 2, 2021