Painkillers double the risk of internal bleeding for patients on blood-thinning medication

If you are taking blood-thinning medication, it’s worth paying close attention to labels when dealing with headaches, back pain, or arthritis. New research from Aarhus University indicates that non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, diclofenac, or naproxen, double the risk of internal bleeding for patients on blood thinners.

Published in the *European Heart Journal*, the study is the largest of its kind to date. Researchers from the Department of Clinical Medicine at Aarhus University analysed data from Danish nationwide registries on 51,794 individuals treated with blood-thinning medication for blood clots between 2012 and 2022.

"We found that patients taking blood-thinning medication for blood clots in the legs or lungs had double the risk of bleeding when also using NSAIDs, compared to those who did not use NSAIDs. This increased bleeding risk was not limited to the gastrointestinal system but also affected other organs,” says Søren Riis Petersen, a medical research student who, along with Associate Professor Morten Schmidt from the Department of Clinical Medicine, led the study.

It is important that patients consult their doctor before taking NSAID painkillers while on blood-thinning medication, emphasises Associate Professor Morten Schmidt, who conducted the study alongside Søren Riis Petersen. Photo: Simon Fischel, Health AU.

Overall, the researchers found that the risk of internal bleeding was 2.09 times higher for those taking both NSAIDs and blood-thinning medication compared to those on blood thinners alone. The study also highlighted differences in where the bleeding occurred. The risk of bleeding in the brain was 3.22 times higher, gastrointestinal bleeding was 2.24 times higher, and lung bleeding increased by 1.36 times.

“We also observed nearly a threefold increase in the risk of anaemia caused by bleeding. Our research emphasises the importance of caution when prescribing pain relief or anti-inflammatory drugs for patients on blood-thinning medication. We strongly recommend that patients consult their doctor before taking NSAIDs alongside blood-thinning medication,” adds Søren Riis Petersen.

The researchers also urge healthcare providers to consider safer alternatives, such as paracetamol or physiotherapy, before prescribing NSAIDs.

Behind the research results:

Study Type: This is a nationwide registry-based study of more than 50,000 adult patients who began blood-thinning treatment for a blood clot in the legs or lungs during the period 2012–2022. The study design is a so-called prospective cohort study.

Collaborators: A collaboration between the Department of Clinical Epidemiology at Aarhus University Hospital, the Department of Cardiology at Aarhus University Hospital, and the Regional Hospital in Gødstrup.

External Funding: Novo Nordisk Foundation.

Contact

Associate Professor Morten Schmidt
Aarhus University, Department of Clinical Medicine,
Department of Clinical Epidemiology
Phone: (+45) 41 28 99 55
Mail: morten.schmidt@clin.au.dk

This text is based on machine translation

Facts about the study

The research is based on data from Danish nationwide registries on 51,794 individuals who received blood-thinning medication to treat blood clots in the legs or lungs between 2012 and 2022.
In Denmark, diclofenac and naproxen are prescription-only, and approximately 75% of ibuprofen is prescribed rather than purchased over the counter. This enabled researchers to compare the proportion of individuals taking blood-thinning medication who later experienced internal bleeding while using NSAIDs, compared to those who did not.
Overall, the researchers found that the risk of bleeding was 2.09 times higher for those taking both NSAIDs and blood-thinning medication compared to those taking only blood thinners. The risk associated with ibuprofen was 1.79 times higher, diclofenac increased the risk by 3.3 times, and naproxen by 4.1 times.
The risk of gastrointestinal bleeding with NSAID use was 2.24 times higher. The risk of bleeding in the brain was 3.22 times higher, in the lungs it increased by 1.36 times, and in the urinary tract the risk was 1.57 times higher.
The researchers examined several types of blood-thinning medication — including rivaroxaban, apixaban, dabigatran, edoxaban, and warfarin — and found a similar risk profile.