Blue urine is uncommon but almost always has a straightforward explanation. The most likely cause is a medication or supplement you’re taking. Less often, a bacterial infection, a food dye, or (rarely) a genetic condition can be responsible. In most cases, the color change is harmless and resolves on its own once the cause is removed.
Medications That Turn Urine Blue
The single most common reason for blue or blue-green urine is a medication. Several widely prescribed drugs can do this:
- Amitriptyline, a tricyclic antidepressant, can produce greenish-blue urine.
- Methylene blue, a dye used medically for over a century, reliably turns urine blue or green. It’s found in some diagnostic tests and supplements marketed for cognitive health. If you’ve swallowed it in any form, expect blue-green urine (and possibly stool) until it clears your system.
- Indomethacin, a nonsteroidal anti-inflammatory drug used for gout and arthritis, can cause green or blue-tinged urine.
- Cimetidine, an acid reflux and ulcer treatment, is another known cause of greenish-blue urine.
- Triamterene, a diuretic (water pill), can produce the same color shift.
- Propofol, an anesthetic used in hospitals, causes green urine in roughly 57% of documented color-change cases. If you’ve recently had surgery or a procedure requiring sedation, this could be the explanation. The discoloration typically clears within 24 hours after the drug is stopped.
If you started any new medication, supplement, or vitamin in the days before you noticed the change, check the label or look it up. Drug-related color changes are cosmetic, not dangerous, and they stop once you finish the medication.
Food Dyes and Supplements
Artificial food dyes, particularly blue and green varieties, can pass through your system and tint your urine. This is more likely if you consumed a large amount of brightly colored candy, frosting, sports drinks, or novelty foods. The effect is temporary and completely harmless.
Methylene blue also shows up outside of medicine. It’s sold as a supplement promoted for brain health and mitochondrial function. MD Anderson Cancer Center notes that swallowing methylene blue will turn your urine and stool green until it’s fully out of your system, and this is normal. If you’ve been taking a supplement with a deep blue color, that’s very likely your answer.
Bacterial Infections
A type of bacteria called Pseudomonas aeruginosa produces a blue pigment as a natural byproduct of its metabolism. If this bacterium colonizes the urinary tract, it can give urine a blue-green tint. Pseudomonas infections are most common in hospital settings and in people with weakened immune systems, those recovering from burns, or people with chronic conditions like cystic fibrosis.
A Pseudomonas urinary tract infection won’t just change your urine color. You’d typically also have symptoms like pain or burning during urination, frequent urges to urinate, fever, or cloudy and foul-smelling urine. If you have blue-green urine along with any of these symptoms, especially after a hospital stay or catheter use, it’s worth getting a urine culture to check for infection. These infections require targeted antibiotics.
Blue Diaper Syndrome
There is one rare genetic condition that causes genuinely blue urine. Blue diaper syndrome is a metabolic disorder where the intestines can’t properly absorb an amino acid called tryptophan. When unabsorbed tryptophan reaches bacteria in the gut, they break it down into compounds called indicans, which turn blue when they hit the urine.
This condition is diagnosed in infancy, not adulthood. Parents notice blue stains on their baby’s diapers. Other signs include digestive problems, fever, irritability, failure to thrive, and sometimes vision problems. The condition can also cause dangerously high calcium levels in the blood, which over time may damage the kidneys. It’s inherited in an autosomal recessive or X-linked recessive pattern, meaning both parents carry the gene. If you’re an adult noticing blue urine for the first time, this is almost certainly not the cause.
How to Figure Out Your Cause
Start with the simplest explanation. Think back over the past 24 to 48 hours: did you take any new medication, supplement, or multivitamin? Did you eat or drink anything with intense artificial coloring? If you can identify either one, the mystery is likely solved. Stop the supplement or wait for the dye to clear, and your urine should return to normal within a day or two.
If you can’t trace it to a medication or food, pay attention to other symptoms. Blue or green urine with pain, burning, fever, or foul smell points toward infection. Blue urine that persists for more than a few days without any obvious dietary or medication cause is worth a urine test to rule out bacterial colonization or other issues.
Blood in the urine, dark brown or orange urine, or urine color changes paired with yellowing skin and pale stools are separate warning signs that suggest liver or kidney problems and need prompt evaluation. Blue urine on its own, without those additional symptoms, is almost never a sign of something dangerous.