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General Practice 2023

Black urine: 7 main causes and what to do

Black urine: 7 main causes and what to do
Black urine: 7 main causes and what to do

Although it may cause concern, the appearance of black urine is most often caused by minor changes, such as eating certain foods or using new medications prescribed by a doctor.

However, this urine color can also be caused by more serious he alth problems such as Haff's disease, liver problems or skin cancer, for example. So, if black urine appears for more than 2 days or if it is accompanied by other symptoms, it is advisable to go to the general practitioner to identify the cause and start the appropriate treatment.


The main causes of black urine are:

1. Eating some foods

Some foods can make the urine darker due to the presence of natural or artificial dyes, such as rhubarb, fava beans and aloe, for example, not being a cause for concern.

Furthermore, foods rich in sorbitol such as apples, pears, peaches and plums, as well as sugar-free foods such as gum, ice cream or candy can also change the color of urine to black when consumed in excess. However, when sorbitol is in very high amounts it also causes stomach pain, cramps and diarrhea.

Using copper pans for cooking can also cause black urine in some people, especially those who cannot metabolize the mineral, eliminating it in high amounts in the urine, which can turn the urine black.

What to do: If the person notices that the urine has turned black after a meal rich in this type of food, despite not being a cause for concern, it is recommended to avoid consuming these foods, opting for others that may have nutritional or similar characteristics.

2. Use of medication

Frequent use of some medicines can also result in black urine and this usually happens as a consequence of frequent contact with some chemicals present in medicines. Some of the drugs or chemicals that can cause black urine are:

  • Phenacetin: is present in many analgesics and when used frequently leads to the destruction of hemoglobin in the blood, which is eliminated in the urine, causing a very dark color;
  • Levodopa: is a drug used in Parkinson's treatment that contains L-dopa, which can make the urine very dark;
  • Phenol: this substance normally enters the body through repeated contact with disinfectant or cleaning products, so it is recommended to wear gloves when using this type of product;
  • Laxatives: some contain cascara or senna, two substances that when used in excess can make the urine very dark;
  • Chloroquine and Primaquine: these are drugs used in the treatment of malaria that can cause black urine as a side effect;
  • Furazolidone, Metronidazole or Nitrofurantoin: these are antibiotics that can change the color of urine, ranging from dark red to black;
  • Methyldopa: It is a medication for high blood pressure that releases metabolites in the urine that, when in contact with the bleach used to clean the toilet, can cause black urine.

In some cases, povidone-iodine, which is a liquid widely used to cleanse some wounds, when used on very large areas of skin can be absorbed by the body and eliminated in the urine, causing the black color.

What to do: When black urine is caused by medication, it is recommended to consult the doctor who indicated them to evaluate the possibility of changing the medication, adjusting the dose or suspension of use.


3. Haff's Disease

Haff's disease has black urine as one of its main symptoms and is a rare disease caused by a thermostable biological toxin that can be found in some freshwater fish and crustaceans.

The presence of this toxin in the body can cause the destruction of muscle cells, causing intense pain, muscle stiffness and numbness, as well as changing the color of urine due to kidney impairment. Learn about other symptoms indicative of Haff's disease.

What to do: Symptoms of Haff disease appear a few hours after contact with the toxin. therefore, if symptoms related to the disease appear after consuming fish or freshwater crustaceans, it is recommended to go to the nearest hospital to start treatment, which consists of hydration and use of analgesics and diuretics to help eliminate the toxin. of the organism.

4. Liver problems

Some changes in the liver, such as cirrhosis and hepatitis, for example, may also have black urine as a symptom, because in these cases, due to altered liver function, it is possible that bilirubin is not properly metabolized to be eliminated in the urine, which makes it darker. Check out other symptoms of liver problems.

What to do: It is important to consult the general practitioner or hepatologist so that an evaluation is carried out and which liver alteration is related to black urine can be identified. Thus, it is possible to indicate the most appropriate treatment, which may involve the use of medication and change in diet according to the cause.

5. Kidney problems

The impairment of kidney function, whether due to infection or as a result of illness, can also result in dark urine, because the kidneys' filtration and absorption process is altered, which can make the urine more concentrated and dark.

What to do: In this case, it is recommended to consult the urologist or general practitioner so that an evaluation of the symptoms and the kidneys is carried out and, thus, it is possible to identify the cause and start the most appropriate treatment, which varies according to the cause, and the use of antibiotics may be indicated in the case of infection, use of diuretic and antihypertensive drugs, and change in eating habits, for example.

See the following video for some nutrition tips for when you have kidney problems:

6. Alkaptonuria

Alkaptonuria, also called ochronosis, is a rare genetic disease that can also cause black urine, because there is accumulation in the body of a substance, homogentisic acid, due to the lack of an enzyme, which can be eliminated urine, making it dark, in addition to leading to the appearance of dark spots in the white part of the eye and around the ear, and cartilage stiffness.

What to do: Alkaptonuria has no cure, however treatment aims to relieve symptoms related to the disease and promote the person's quality of life. recommended by the doctor the use of anti-inflammatories and analgesics, physiotherapy sessions and changes in diet, being indicated to increase the consumption of foods rich in vitamin C. See more details of the treatment of alkaptonuria.

7. Skin cancer

Skin cancer can also have black urine as one of the signs and symptoms, because excess melanin, which is the substance responsible for skin pigmentation, can be eliminated in the urine, which becomes dark due to to the oxidation of melanin present when it comes into contact with air.

What to do: In the case of skin cancer, it is important to follow the treatment guidelines given by the oncologist or dermatologist, which may involve performing surgery to remove the cancerous lesion present on the skin, followed by chemo sessions and radiotherapy. Learn more about skin cancer treatment.

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