Warfarin and anti-inflammatory painkillers (NSAIDs): bleeding risk explained

Warfarin is an anticoagulant. The NHS describes it as a medicine that helps prevent blood clots, used for conditions such as deep vein thrombosis, pulmonary embolism, atrial fibrillation and mechanical heart valves. It works by slowing the clotting process, so the body forms clots less readily.

NSAIDs are a large group of painkillers that also reduce inflammation. Ibuprofen, naproxen and diclofenac are the best known, and aspirin belongs to the same family. As well as easing pain, NSAIDs can irritate the lining of the stomach and interfere with platelets, the small blood cells that help form a plug when a blood vessel is damaged.

An interaction is simply a situation where two medicines affect each other or add up in an unwanted way. Here the problem is mainly additive: warfarin slows clotting and NSAIDs make the stomach lining more fragile and platelets less sticky. The BNF describes this as both medicines increasing the risk of bleeding, and classes it as a severe interaction for each of the common NSAIDs.

The main side effect of warfarin is an increased risk of bleeding, as the NHS says on its warfarin page. Most people on a stable dose never have a serious bleed, because blood tests are used to keep the effect in a target range. The concern with NSAIDs is that they add a second route to bleeding that the blood tests do not track.

The NHS ibuprofen page lists stomach ulcers or bleeding inside the stomach among the possible serious side effects of ibuprofen, with symptoms that include tummy pain, vomiting blood or black, sticky, tar-like poo. It also says the risk of serious side effects is higher with a high dose or long-term use.

There is a second, quieter issue. Some medicines change how much warfarin is active in the blood. Whenever a new medicine is added, the clinic may want an earlier INR test to check that clotting is still in range. That is one more reason for the NHS advice to speak to a doctor before starting anything new.

The category is wider than the familiar brand names. NSAIDs appear as tablets, capsules, liquids, gels, sprays and combination cold and flu remedies. Because the active ingredient may not be obvious on the front of the box, checking the ingredient list or asking a pharmacist is worth the minute it takes.

• Ibuprofen, including many over-the-counter pain and cold products.

• Naproxen and diclofenac, which are often prescribed for joint and back pain.

• Aspirin taken for pain relief. The NHS clopidogrel page, for example, advises against 300mg aspirin for pain unless a doctor has said it is acceptable alongside blood-thinning medicines.

• Low-dose aspirin prescribed on purpose for the heart or stroke prevention is a separate decision made by a doctor who knows the full picture, and should not be stopped or started without advice.

• Topical NSAID gels and sprays. These are absorbed far less than tablets, but it is still sensible to mention them when you check.

The NHS warfarin page lists the symptoms of serious bleeding as blood in your pee or poo, unexplained bruising or nosebleeds, coughing up blood or vomiting blood, and a sudden bad headache with confusion, slurred speech, difficulty moving your arms or legs, or feeling or being sick, which can be signs of bleeding in the brain. It advises calling NHS 111 if you are taking warfarin and have symptoms of bleeding or have had a head injury.

Someone who is collapsing, vomiting a lot of blood or showing signs of a stroke is an emergency, and 999 is the right call, as it would be for anyone. Stomach bleeding does not always look dramatic. The NHS ibuprofen page describes stomach bleeding as causing symptoms that can include tummy pain, shortness of breath, pale skin, vomiting blood or poo that is black, sticky and tar-like, so these can be the first clues, so mention them to a clinician promptly rather than waiting for them to pass.

Pain is common in people who take warfarin, because many of them are older or have long-term conditions. The practical question is what to use instead. The NHS ibuprofen page notes that ibuprofen can cause more side effects than paracetamol and says that if you can take paracetamol it is a good idea to try it first. A pharmacist can confirm whether paracetamol suits you and at what dose alongside your other medicines.

Non-drug measures often help with musculoskeletal pain: heat or cold packs, gentle movement, physiotherapy-guided exercise and pacing activity. For persistent pain, a GP can review the cause and discuss options that take account of the warfarin, including whether a different anticoagulant or a different type of pain treatment might be appropriate for you. Do not stop warfarin yourself.

When a doctor does decide that an NSAID is needed, it is usually for a short period with a review, sometimes with a stomach-protecting medicine. That is a decision for the prescriber, not something to start independently.

In the NHS, warfarin treatment is usually supervised by an anticoagulation clinic or the GP surgery, with regular INR blood tests. The NHS says tests are frequent at the start and, once the dose is stable, usually only needed about every 12 weeks, though some people need them more often. You are also given an anticoagulant alert card, which you should show to doctors, dentists and pharmacists.

Pharmacists are well placed to answer the everyday question of whether a particular off-the-shelf product is suitable. Private clinicians and pharmacies follow the same medicines references, so the safety advice does not change by route, but it helps to share your warfarin treatment record and tell them about your INR results so everyone works from the same information.