Warfarin and anti-inflammatory painkillers (NSAIDs): why the combination needs care

Warfarin is an anticoagulant, sometimes called a blood thinner. The NHS explains that it is used to treat and prevent blood clots, including in the veins (deep vein thrombosis) and the lungs (pulmonary embolism), and to reduce the risk of clots in conditions such as atrial fibrillation or a mechanical heart valve. The NHS anticoagulant page adds that although these medicines are often called blood thinners, they do not actually make the blood thinner; they work by interrupting the process that forms clots.

The cost of this benefit is a higher risk of bleeding. The NHS says the main side effect of warfarin is an increased risk of bleeding. NSAIDs such as ibuprofen and aspirin are a separate group of painkillers that, according to the NHS, can sometimes cause stomach ulcers or bleeding inside the stomach. Because both can cause bleeding, taking them together is a combination that the NHS flags as something that may not mix well, and which should be discussed with a pharmacist, doctor or anticoagulant clinic before it is used.

The guidance on this page is general. Your own situation, including the reason you take warfarin, your most recent INR test results and any history of ulcers or kidney problems, determines what is safe for you, and only your prescriber or pharmacist can judge it.

On warfarin, the NHS says there are medicines, remedies and supplements that may not mix well with warfarin, and lists NSAIDs such as ibuprofen or aspirin, antibiotics, antidepressants, medicines for heart problems, medicines for stomach ulcers, medicines for fungal infections and cholesterol-lowering medicines such as statins. It adds that you should not take the herbal remedy St John's wort or vitamin K supplements while taking warfarin.

The NHS ibuprofen page lists anticoagulants such as warfarin among the medicines that may not mix well with ibuprofen, together with steroid medicines, antidepressants and medicines to lower blood pressure. It also lists a stomach ulcer, or a history of stomach ulcers, as a reason ibuprofen may not be suitable, and lists heart, liver or kidney conditions and problems with blood clotting among other reasons.

The NHS aspirin page lists anticoagulants such as warfarin or rivaroxaban, some steroid medicines, some antidepressants, some medicines to lower blood pressure, methotrexate and other NSAIDs such as naproxen or ibuprofen as medicines that may not mix well with aspirin. The NHS anticoagulant page makes the more general point that other medicines, including prescription and over-the-counter ones, can affect how an anticoagulant works, and advises speaking to your GP, anticoagulant clinic or pharmacist before taking any other medicines.

It is tempting to assume that paracetamol is always the safe alternative, and it is the painkiller many prescribers suggest first. The NHS paracetamol page nonetheless lists warfarin among the medicines that may not mix well with paracetamol, alongside some cold and flu medicines that contain paracetamol, so the same advice to check applies. A pharmacist can look at your full medicines list and advise what is suitable and at what dose.

Several other things may contain an NSAID or aspirin without being obvious: cold and flu remedies, gels and sprays, and combination painkillers. The NHS notes that ibuprofen is available as tablets, capsules, gels, sprays, liquid and granules, and that you are less likely to get side effects from the gel or spray. Whether a gel is suitable while on warfarin is a question for a pharmacist; do not assume it is.

Low-dose aspirin prescribed for heart or stroke protection is a separate matter. The NHS anticoagulant page notes that anticoagulants are different to antiplatelet medicines, such as low-dose aspirin and clopidogrel. If a doctor has prescribed both, that decision has been made on purpose with the bleeding risk in mind. Do not start or stop either medicine without advice.

The NHS lists symptoms of serious bleeding with warfarin as blood in the pee or poo, unexplained bruising or nosebleeds, coughing up blood or vomiting blood, and a sudden bad headache with confusion, slurred speech, difficulty moving the arms or legs, or feeling or being sick, which can be signs of bleeding in the brain.

On ibuprofen, the NHS lists possible serious side effects as stomach ulcers or bleeding inside the stomach, causing symptoms such as tummy pain, shortness of breath, pale skin, vomiting blood or poo that is black, sticky and tar-like, as well as an allergic reaction and kidney problems with shortness of breath, blood in the pee or swelling in the ankles, feet or hands.

The NHS says to call NHS 111 if you are taking warfarin and you have symptoms of bleeding, have had a head injury, or think you might be having any other serious side effects. For vomiting blood or bright red blood, black tarry stools, or sudden severe symptoms such as those of bleeding in the brain, call 999 or go to A&E. The NHS stomach ulcer page, for example, lists vomiting bright red blood or vomit that looks like ground coffee, poo that is black, sticky and very smelly, and severe tummy pain as reasons to call 999 or go to A&E.

The NHS says you will be given an anticoagulant alert card because warfarin may put you at risk of bleeding, and that you should always carry it and show it to your doctor or dentist before any medical or dental procedures. It also says that while taking warfarin you will need regular INR blood tests, which measure how quickly your blood clots and check you are on the right dose, and that your dose may change based on the results.

• Ask a pharmacist before buying any over-the-counter painkiller, cold remedy or supplement.

• Tell every doctor, dentist, nurse and pharmacist that you take warfarin.

• Carry your anticoagulant alert card and keep a current medicines list.

• If your doctor starts you on a new medicine, such as a short course of antibiotics, ask whether your INR should be checked, because the NHS lists several medicine types that may not mix well with warfarin.

• Do not stop warfarin yourself because of an interaction worry; speak to your anticoagulant clinic or GP.

In the NHS the anticoagulant clinic, GP surgery or community pharmacy is the usual place to ask about interactions, and an urgent query out of hours can go to NHS 111. Private doctors and pharmacies can answer the same questions, but they should be told about your warfarin and your recent INR results, and any medicine they prescribe should be recorded with your own GP so the whole picture stays in one place.