What should you know about dark grey urine?

Urine may appear grey or unusually dark because it is concentrated after fluid loss, or because a food dye, supplement, medicine, cleaning product or container has changed how it looks. Lighting can also distort colour. Health problems affecting the liver or bile pathways, including hepatitis A or hepatitis B, can cause dark urine and may also cause yellow skin or eyes, pale stools, nausea, itching or marked tiredness. Colour alone does not show which explanation applies. Compare a fresh sample in a clean, clear container and consider whether the change is genuinely in the urine.

Drink water regularly if you can do so safely, particularly after sweating, vomiting or diarrhoea. Review new medicines and supplements, but do not discontinue prescribed treatment without professional advice. Note the colour, smell, amount, timing and associated symptoms. If the urine returns to its usual colour after replacing fluids and there are no other symptoms, continue to observe it. If the change remains, contact a clinician for a urine assessment and any other tests they consider appropriate.

Get urgent help for confusion, fainting, severe weakness, inability to keep fluids down, very little urine, severe pain, fever with a very unwell feeling, or yellow skin or eyes. Arrange prompt medical advice when grey or dark urine persists, recurs without an obvious explanation, or occurs with pale stools, abdominal discomfort or vomiting. Do not wait for colour alone to become clearer if you feel significantly unwell.

Could a medicine, supplement, food or container explain the appearance? Should I have urine or liver tests? How much should I drink, and which changes would require same-day care?