Dozens of commonly prescribed drugs and over-the-counter supplements can turn urine vivid shades of orange, red, green, blue, brown, or even purple. In most cases the color change is harmless and disappears once the medication is stopped. The phenomenon happens because the body excretes certain drug metabolites through the kidneys, and those metabolites carry their own pigments into the urine. Knowing which medications cause which colors can save you an unnecessary trip to the emergency room and help you recognize the rare situations that actually do warrant concern.
Orange and Red Urine
The most frequently encountered medication-related color shift is orange or reddish urine, and the drug most often responsible is phenazopyridine, sold over the counter under brand names like Azo and Pyridium. Phenazopyridine is a bladder analgesic used to relieve the burning sensation that comes with urinary tract infections. It works locally on the lining of the urinary tract, and its azo-dye chemistry stains everything it touches. Your urine can turn deep orange within hours of taking the first dose, and the dye can also stain underwear, contact lenses, and even tears if enough of it accumulates. The effect is entirely benign and clears up once you stop the medication.
Rifampin, an antibiotic used primarily for tuberculosis and certain other serious infections, is another well-known offender. It can turn urine, sweat, saliva, and tears a startling reddish-orange. Healthcare providers usually warn patients about this in advance because the staining can ruin clothing and alarm people who were not expecting it. Warfarin, the blood thinner, has also been reported to give urine an orange tint, though less dramatically.
Doxorubicin, a chemotherapy agent, causes urine to appear red or pink for a day or two after infusion. Because this drug is given under close medical supervision, patients are almost always told to expect it. The key distinction with any reddish or orange urine is whether you recently started one of these medications. If you have not, red or pink urine could signal blood in the urine, which is a different matter entirely and worth investigating promptly.
Bright Yellow and Neon Urine
If you have ever taken a multivitamin and noticed your urine turning an almost fluorescent yellow shortly afterward, you have seen riboflavin at work. Riboflavin, also known as vitamin B2, is a water-soluble vitamin, and any amount your body does not immediately need is rapidly flushed out through the kidneys. The excess riboflavin is itself intensely yellow, and it can make urine look almost neon compared to its usual straw color. A study on passive urine-color monitoring noted that riboflavin is one of the supplements known to distort urine color enough to confound hydration assessments, because the vivid hue masks the pale shade that would normally indicate good hydration.1Smart Health. Automated supplement correction in passive urine color measurement device for real-time hydration testing
This is worth knowing if you use urine color as a rough hydration gauge, which many athletes and health-conscious people do. On days you take a B-complex supplement, your urine may look dark yellow even though you are perfectly well hydrated. The color is just riboflavin, not a sign of dehydration. Similarly, some B-complex formulations contain enough B2 to keep urine bright yellow for several hours, so the timing of your dose relative to when you check the color matters.
Green and Blue Urine
Green urine is uncommon enough that it tends to alarm both patients and clinicians, but it has a surprisingly long list of medication-related causes. Propofol, the intravenous anesthetic widely used during surgeries and sedation procedures, is one of the best-documented culprits. When the body’s liver pathways are overwhelmed during or after anesthesia, propofol is eliminated through alternative routes that produce green-pigmented metabolites in the urine. This side effect occurs in fewer than one in a hundred cases and is considered benign, non-toxic to the kidneys, and fully reversible once the drug clears the system.2PubMed Central. Green Urine Due to Propofol: A Case Report with Review of Literature
Methylene blue is another classic cause, and it is practically designed to turn things blue. Used both as a diagnostic dye during surgery and as a treatment for certain poisonings, methylene blue is excreted in the urine and can give it a striking blue or blue-green appearance. When the blue dye mixes with the natural yellow of urine, the result is often green rather than pure blue.
Beyond propofol and methylene blue, several other medications have been linked to green or blue-green urine. Amitriptyline (a tricyclic antidepressant), cimetidine (a heartburn medication), indomethacin (an anti-inflammatory), promethazine (an antihistamine and anti-nausea drug), and triamterene (a potassium-sparing diuretic) have all been reported to cause green discoloration.3PubMed Central. Green urine: A cause for concern? The Lancet has also listed amitriptyline, cimetidine, indomethacin, and methylene blue among substances that produce green or blue urine.4The Lancet. Green urine
Not all green urine is medication-related, though. Pseudomonas bacterial infections of the urinary tract produce a pigment called pyocyanin that can turn urine greenish, and a rare inherited condition called Hartnup disease can do the same.4The Lancet. Green urine A clinical case report on blue-green urine emphasized that the key to sorting out benign drug-related causes from pathological ones is a careful medication history: if the patient recently started or is currently on any of the known offenders, the color change is almost certainly the drug.5PubMed Central. Diagnostic Approach to Abnormal Urine Colors: Lessons From a Case of Blue-Green Urine
Dark Brown and Black Urine
Metronidazole, a widely prescribed antibiotic used for infections ranging from dental abscesses to Clostridioides difficile colitis, is the medication most associated with dark brown or cola-colored urine. The discoloration comes from a metabolite of the drug that darkens when it oxidizes. In one documented case, a patient being treated for C. difficile developed cola-colored urine after starting metronidazole.6PubMed Central. Urine Discoloration Associated With Metronidazole: A Rare Occurrence An earlier report described a patient with amebic dysentery who passed dark-brown urine throughout a five-day course of metronidazole at 750 mg three times daily; the discoloration stopped promptly once the drug was discontinued.7JAMA. Dark Urine Related to Metronidazole Therapy
Nitrofurantoin, another antibiotic commonly used for urinary tract infections, can darken urine to a rust or brownish color. Chloroquine and primaquine, antimalarial drugs, have also been linked to brown or dark urine. And levodopa, used for Parkinson’s disease, can produce urine that darkens to brown or black after standing in the toilet for a while, even if it looked relatively normal at first. The darkening on standing is a characteristic clue that the color is drug-related rather than a sign of bleeding or liver disease.
Brown or very dark urine that appears without any obvious medication explanation deserves medical attention. It can indicate old blood in the urinary tract, certain liver or muscle problems, or severe dehydration. The presence or absence of a plausible medication history is the quickest way to triage whether the color is alarming or routine.
Purple Urine Bag Syndrome
Purple urine bag syndrome is a striking phenomenon that mostly affects people with long-term urinary catheters. Rather than the urine itself turning purple inside the body, the color change happens in the catheter tubing and collection bag. Certain bacteria that colonize the urinary tract produce enzymes that convert tryptophan metabolites into the pigments indigo (blue) and indirubin (red). When those two pigments mix on the plastic surfaces of the drainage system, the result is a dramatic purple color.
The condition is associated with bacterial urinary tract infections, alkaline urine with a pH of 7.0 or higher, constipation, high bacterial counts, and prolonged catheterization. It is more common in women and in bedridden patients.8PubMed Central. An update on purple urine bag syndrome Despite how alarming it looks, the purple color itself is not dangerous. The underlying urinary infection usually needs treatment, and resolving the infection and changing the catheter system clears the discoloration. Caregivers and nursing home staff encounter it periodically, but it can be deeply unsettling for family members seeing it for the first time.
When a Color Change Actually Matters
The general rule is simple: if you recently started a new medication or supplement and your urine changes color, the two are almost certainly connected, and the color change is harmless. Check the medication’s package insert or patient information sheet. Drug-induced urine discoloration is listed as a known side effect for all the medications discussed here, and it resolves once the drug is stopped or the dose is reduced.
Color changes that deserve a call to your doctor include:
- Red or pink urine with no medication explanation, which could indicate blood (hematuria) from kidney stones, infections, or more serious conditions.
- Dark brown urine accompanied by pale stools and yellowing of the skin or eyes, which could point to a liver or bile duct problem.
- Tea-colored urine after intense exercise or muscle injury, which could indicate rhabdomyolysis, a potentially dangerous breakdown of muscle tissue.
- Cloudy or milky urine with pain, fever, or a foul smell, which suggests infection rather than a drug effect.
The pattern that separates medication-related color changes from worrisome ones is consistency and timing. Drug effects appear when you start the medication, remain stable for the duration of treatment, and vanish when you stop. Pathological color changes tend to fluctuate, worsen, or come with other symptoms like pain, fever, or changes in how much you urinate.
How Colored Urine Can Interfere With Lab Tests
An underappreciated consequence of medication-induced urine color changes is that they can throw off common laboratory tests. Urine dipstick tests, the quick screening strips used in clinics and hospitals, rely on chemical color reactions to detect things like blood, protein, glucose, and white blood cells. When the urine is already deeply pigmented from a drug, those color reactions become harder to read accurately, and false results become more likely.
One well-documented example involves antibiotics and the leucocyte esterase test on dipstick strips. A study in the BMJ found that commonly used antibiotics could induce false positive results for white blood cells on dipstick testing, leading to the conclusion that urine culture is the only reliable method for diagnosing urinary infections in patients taking these drugs.9PubMed. False positive results for leucocytes in urine dipstick test with common antibiotics If your doctor orders a urine test while you are on a medication known to color the urine, mentioning the medication upfront can help the lab interpret results correctly or choose a different testing method.
Phenazopyridine is a particularly notorious interferer. Its intense orange dye can mask or distort several dipstick reactions, which is why healthcare providers often ask patients to stop taking it before providing a urine sample. If you are using an over-the-counter product like Azo for UTI pain relief and then visit a clinic for testing, let them know so they can account for it.
Foods and Other Non-Drug Causes
Not every surprising urine color comes from a pill bottle. Beets are famous for turning urine pink or reddish in some people, a phenomenon sometimes called beeturia. It affects a subset of the population more than others, and whether it happens to you depends partly on the acidity of your stomach and how you metabolize the pigments in beets. Blackberries and rhubarb can produce similar effects. Asparagus does not change color, but it gives urine a distinctive sulfurous odor that some people can detect and others cannot, depending on their genetics.
Beet juice has been flagged alongside riboflavin as a substance that distorts urine color enough to confound hydration-monitoring devices.1Smart Health. Automated supplement correction in passive urine color measurement device for real-time hydration testing Artificial food colorings, particularly blue and green dyes found in candy, sports drinks, and some processed foods, occasionally turn up as surprise causes of green or blue urine. Food dyes like FD&C Blue No. 1, used widely in blue-colored beverages and candies, pass through the body largely intact and can tint the urine noticeably in people who consume enough of them. The Lancet’s list of substances that produce green urine includes food coloring alongside medications.4The Lancet. Green urine
Why Your Doctor Might Not Warn You
Given how many medications can change urine color, you might wonder why your pharmacist or doctor does not always mention it. Part of the reason is that urine discoloration is classified as a cosmetic side effect rather than a clinical one. It does not affect how the drug works, does not damage the kidneys, and does not require a change in treatment. In a ten-minute office visit, providers tend to focus on side effects that might prompt a patient to stop taking the drug or that could cause actual harm: nausea, allergic reactions, drug interactions. Urine color gets relegated to the fine print.
That said, some medications produce color changes alarming enough that good practice dictates a heads-up. Rifampin’s reddish-orange staining of bodily fluids and metronidazole’s dark brown discoloration both appear startling enough that patients have presented to emergency departments worried about internal bleeding. A brief warning at the pharmacy counter can prevent that anxiety. If you start a new medication and notice something unusual in the toilet bowl, checking the drug’s patient information leaflet is the fastest way to confirm whether the color change is listed. If it is, you are almost certainly fine. If it is not, a quick call to your provider is reasonable.