What causes dark urine?

Urine becomes darker and more concentrated when you lose fluid through sweating, vomiting, diarrhoea, fever, or not drinking enough. Heat exhaustion can combine fluid loss with weakness, dizziness, headache, and heavy sweating. Foods, supplements, and medicines can also change urine colour. Brown or tea-coloured urine may occur when bile pigments enter urine during hepatitis A or hepatitis B, especially with yellow skin or eyes and pale stools.

Red or cola-coloured urine can reflect blood or muscle pigments. G6PD deficiency can cause red-cell breakdown after particular triggers. Colour alone cannot identify the cause, so persistent or unexplained change deserves testing.

If you feel well and dehydration is plausible, rest somewhere cool and drink fluids gradually. Avoid strenuous exercise until unusually dark urine has been assessed, particularly after heat exposure or muscle pain. Make a note of recent foods, supplements, medicines, illness, and urine changes. Do not stop a prescribed medicine without speaking to a clinician.

Seek urgent help for confusion, fainting, severe weakness, inability to keep fluids down, very little urine, severe abdominal or back pain, or dark urine with yellow skin or eyes. Prompt medical review is needed for blood, burning, fever, swelling, muscle pain, or urine that stays dark despite drinking. Heat-related symptoms with worsening weakness require urgent assessment.

Ask whether you need urine and blood tests to check hydration, infection, liver function, blood-cell breakdown, or muscle injury. Tell the clinician when the colour changed, your fluid intake, recent heat or exercise, pain or fever, and every medicine and supplement you take.