Antibiotics and dark urine

Check the medicine leaflet and contact a pharmacist or prescriber if the colour change is new, persists after drinking fluids, or occurs with other symptoms. Do not change the dose merely because the urine looks darker unless a clinician tells you to, but seek urgent help for the warning signs below.

Concentrated urine is deep yellow or amber and often follows reduced drinking, fever, vomiting, or diarrhoea. Some antibiotics or their breakdown products can alter urine colour without harming the urinary system. Brown, tea-coloured, red, or cloudy urine has other possible causes, including blood, liver inflammation, muscle injury, or a urinary problem.

The timing matters. Note when the change began, the exact colour, your fluid intake, and whether there is pain, fever, yellowing of the eyes, pale stools, reduced urine, or unusual tiredness. These details help distinguish a medicine effect from an illness that needs testing.

Drink fluids regularly unless you have been told to restrict them because of a heart, kidney, or liver condition. Compare the colour after hydration and read the antibiotic leaflet for listed colour changes. Keep the packet or a photo of its label available when seeking advice.

Call the prescribing clinic or a pharmacist the same day if the urine remains dark, you feel unwell, or you are unsure whether the antibiotic is responsible. They may review other medicines and decide whether urine, blood, liver, or kidney checks are appropriate. Never take someone else's antibiotic or double a missed dose.

Get urgent medical assessment for dark urine with yellow skin or eyes, pale stools, severe abdominal or back pain, visible blood or clots, marked weakness, repeated vomiting, very little urine, confusion, or swelling. These features can signal liver, kidney, urinary, or muscle complications rather than a simple colour change.

Call emergency services for trouble breathing, swelling of the lips, tongue, face, or throat, collapse, or a rapidly spreading blistering or peeling rash. These are emergency features of a serious medicine reaction.

Ask whether your particular antibiotic is known to change urine colour, whether your infection could explain it, and whether you need urine or blood tests. Confirm what to do with the next dose, how to manage missed doses, and which symptoms should prompt an immediate reassessment.