Black urine is rare and almost always signals something that needs medical attention. The color can come from medications, a genetic condition, severe liver problems, or other medical causes. True black urine (not just dark yellow from dehydration) is unusual enough that it warrants a prompt call to your doctor or a visit to urgent care.
Why Urine Turns Black
Normal urine ranges from pale yellow to amber, depending on how hydrated you are. When urine appears black or very dark brown, something is adding pigment that doesn’t belong there. That pigment can come from a chemical your body can’t break down properly, a medication being processed through your kidneys, or a byproduct of tissue damage in your liver or elsewhere.
It’s worth noting the difference between concentrated dark yellow urine (which happens when you’re dehydrated) and genuinely black or cola-colored urine. Dehydration makes urine darker on the yellow-amber spectrum. Black urine looks distinctly different, sometimes closer to cola, tea, or ink.
Medications That Darken Urine
Several common medications can turn urine very dark brown or black. The antibiotics metronidazole and nitrofurantoin are well-known culprits. Metronidazole is frequently prescribed for bacterial infections and certain parasites; nitrofurantoin is a go-to for urinary tract infections. Both can produce dramatically dark urine that looks alarming but is a harmless side effect of how the drug is processed.
Other medications in the same category include certain malaria drugs, some laxatives containing senna, and methyldopa (a blood pressure medication). If you recently started a new prescription and notice your urine turning very dark, check the medication’s side effects or call your pharmacist. In most of these cases, the color change resolves once you stop taking the drug.
Alkaptonuria: The “Black Urine Disease”
Alkaptonuria is a rare genetic condition sometimes called black urine disease. People with it lack a working version of the enzyme that breaks down a substance called homogentisic acid, which is a normal byproduct of protein digestion. Without that enzyme, homogentisic acid builds up in the body and gets excreted through the kidneys. The telltale sign: urine that looks normal when it first comes out but turns black after sitting and being exposed to air. The oxidation process is what triggers the color change.
This condition affects roughly 1 in 250,000 to 1 in 1,000,000 people in most populations, though it’s significantly more common in Slovakia and the Dominican Republic, where rates reach about 1 in 19,000. Parents sometimes notice the first clue in infancy when diapers develop dark stains after sitting in the hamper.
Beyond the urine color, the real concern with alkaptonuria is long-term damage. The same acid that darkens urine also deposits in cartilage, tendons, and heart valves over decades, causing a progressive darkening and stiffening of connective tissue called ochronosis. Joint pain and arthritis typically develop by a person’s 30s or 40s. A clinical trial published in The Lancet Diabetes & Endocrinology found that a once-daily oral medication reduced the problematic acid in urine by over 99% and slowed disease progression, giving people with alkaptonuria the first real treatment option. The change was so dramatic that researchers couldn’t fully blind the study because patients could see their urine color normalize.
Liver Problems and Dark Urine
Your liver filters waste products from your blood, and when it’s failing or severely inflamed, those waste products can spill into your urine in abnormal amounts. Dark brown or black urine can be one sign of serious liver disease. But it almost never appears alone. Liver-related dark urine typically comes alongside other symptoms: yellowing of the skin or eyes (jaundice), pale or clay-colored stool, persistent nausea, swelling in the belly or ankles, severe fatigue, and easy bruising.
The combination matters. Dark urine plus pale stool is a particularly telling pair, because it suggests bile (which normally colors your stool brown) is being redirected into your bloodstream and filtered through your kidneys instead. If you’re experiencing dark urine along with any of these other symptoms, especially abdominal pain severe enough that you can’t get comfortable, that’s a situation for emergency care.
Other Medical Causes
Severe muscle breakdown, known as rhabdomyolysis, can release a protein called myoglobin into the bloodstream in such large quantities that urine turns dark brown or black. This typically happens after extreme physical exertion, crush injuries, or certain drug reactions. It’s painful and usually obvious: intense muscle soreness, weakness, and very dark urine appearing together.
Certain cancers, particularly melanoma that has spread, can occasionally produce dark pigment that appears in the urine. This is uncommon even among melanoma patients and would occur in the context of advanced disease with other known symptoms.
Severe infections of the urinary tract or kidneys can also darken urine substantially, though this is more often a dark red-brown from blood rather than true black.
How Black Urine Is Diagnosed
A standard urinalysis is usually the first step, which can detect blood, abnormal proteins, bile pigments, and other substances that shouldn’t be there. If alkaptonuria is suspected, more specialized testing measures levels of homogentisic acid in both urine and blood. Modern lab methods using mass spectrometry can identify and quantify the acid with high precision. Genetic testing can confirm alkaptonuria by identifying mutations in the specific gene responsible.
Your doctor will also consider the context: what medications you’re taking, whether you have other symptoms, and how quickly the color change appeared. A medication side effect that started three days after beginning an antibiotic tells a very different story than black urine accompanied by joint pain that’s been building for years.
What You Should Do
If your urine turns black or very dark and you’re currently taking a medication known to cause it, the explanation may be straightforward. Still, mention it to your prescriber at your next opportunity to confirm.
If there’s no obvious medication explanation, collect a urine sample if you can (a clean container works) and contact your doctor promptly. Note whether the urine was dark immediately or darkened after sitting, since that distinction helps narrow the cause. If you’re also experiencing abdominal pain, yellowing skin, confusion, or severe muscle pain, seek care the same day.