You’ve just noticed blood in your urine, and honestly? It’s terrifying. Before you spiral into worst-case scenarios though, here’s something that might not have crossed your mind: it could be your medications. I know that sounds odd—surely your doctor would have mentioned that—but drug-induced haematuria (the medical term for blood in urine) is more common than most people realise, and it often catches patients completely off guard.
Let me walk you through what’s actually going on here, because understanding this might save you considerable anxiety.
The Usual Suspects: Which Medications Commonly Cause This?
Right, so blood thinners are probably the most obvious culprits. If you’re taking warfarin, rivaroxaban, or apixaban—medications prescribed to prevent blood clots—you’re already on something that literally stops your blood from clotting as easily. According to the NHS guidance on anticoagulants, bleeding is a known side effect, and that can show up in your urine.
But here’s where it gets interesting. Aspirin, which loads of people take daily for heart health, can also cause bleeding in the urinary tract. Even at those low 75mg doses. Research published in the British Journal of General Practice found that approximately 3% of patients on long-term aspirin therapy experience some form of urinary tract bleeding.
Then you’ve got cyclophosphamide, a chemotherapy drug that can cause something called haemorrhagic cystitis—basically inflammation and bleeding in the bladder. It’s serious enough that oncologists usually monitor for it specifically. If you’re on this medication and notice pink or red urine, you need to contact your medical team straight away.
Rifampicin, an antibiotic used primarily for tuberculosis, can turn your urine orange-red. Now, this isn’t actually blood—it’s just discolouration from the drug itself—but it looks alarming enough that people frequently ring their GP in a panic. I mention this because not everything that looks like blood necessarily is blood, which brings me to my next point.
When It’s Not Actually Blood (But Looks Exactly Like It)
This might seem like a tangent, but it’s genuinely useful information. Several medications can make your urine look red or pink without any actual bleeding occurring.
Phenazopyridine, which you might know as a urinary pain reliever, turns urine a startling orange-red colour. Completely normal, but nobody warns you adequately beforehand. Certain laxatives containing senna can do similar things. Even beetroot—though obviously not a medication—can cause red urine in some people, a phenomenon that affects about 10-14% of the population.
So before you panic, it’s worth considering: have you started any new medications recently? Changed doses? Your pharmacist can actually be brilliant for these questions, and they’re often easier to reach than your GP.
The Mechanism: Why Do These Drugs Cause Bleeding?
Let’s talk about how this actually happens, because understanding the ‘why’ makes it less mysterious.
Blood thinners work by interfering with your body’s clotting cascade—that’s the series of reactions that normally stops bleeding. When you reduce clotting ability, even tiny blood vessels in your kidneys or bladder can leak small amounts of blood that show up in urine. It’s not necessarily dangerous, but it needs monitoring.
Some medications cause direct irritation or damage to the bladder lining. Cyclophosphamide breaks down into compounds that concentrate in the bladder and can damage the bladder wall. That’s why patients on this drug often receive additional medications specifically to protect the bladder.
Non-steroidal anti-inflammatory drugs—your ibuprofens and naproxens—can cause kidney inflammation or even small ulcers in the urinary tract if used long-term. A 2019 study from researchers at the University of Oxford found that regular NSAID use increased the risk of acute kidney injury, and bleeding can be part of that picture.
Penicillins and other antibiotics occasionally trigger something called interstitial nephritis, an inflammatory reaction in the kidneys that can lead to blood in the urine. It’s relatively rare, but it happens.
What You Should Actually Do About It
Here’s the thing: you shouldn’t just shrug this off, even if you’ve now read this article and think ‘oh, it’s probably my medication.’ Blood in urine always warrants a conversation with a healthcare professional.
That said, don’t necessarily panic either. If you’re on blood thinners and you see a small amount of blood in your urine once, that’s different from seeing large amounts of blood or passing clots. If you’re experiencing pain, fever, or can’t urinate properly, that’s urgent. The NHS page on blood in urine provides clear guidance on when to seek immediate medical attention versus booking a routine appointment.
Your doctor will likely want to test your urine properly—not just eyeball it, but actually analyse it in a lab. They might check your kidney function with blood tests. If you’re on warfarin, they’ll probably check your INR level to see if your blood is thinner than intended.
Sometimes the solution is straightforward: adjusting your medication dose, switching to an alternative drug, or adding a protective medication alongside the problematic one. For people on chemotherapy, there are specific protocols to prevent bladder damage.
It’s worth keeping a record of when you notice blood in your urine, how much, and what colour. I know that sounds unpleasant, but it’s actually useful information for your healthcare team. Is it bright red (suggesting fresh bleeding) or darker, tea-coloured (suggesting the blood has been in your system longer)? Does it happen every time you urinate or just occasionally?
And look, I can’t stress this enough: never stop taking prescribed medication without talking to your doctor first, even if you’re convinced it’s causing problems. Abruptly stopping blood thinners, for instance, could put you at serious risk of stroke or blood clots. The solution isn’t to stop the medication on your own—it’s to work with your medical team to find the right approach.
Sometimes the medication causing the bleeding is literally keeping you alive, and the benefit massively outweighs this side effect. Other times, there’s a perfectly good alternative that won’t cause the same problem. That’s a conversation that needs proper medical input, not internet guesswork—even well-informed internet guesswork like this article.
