Dehydration is one possible cause of dark brown urine, states Healthgrades. Dehydration increases urine concentration by reducing the amount of water in the urine. When the body loses water due to dehydration, the kidneys retain more water as a way of responding to the water loss in order to ensure that enough water is available for the normal functioning of the body. As a result, the kidneys release highly concentrated dark brown urine into the urinary bladder for disposal.
Other than dehydration, causes of dark brown urine include conditions and diseases that affect the urinary tract such as bladder cancer, bladder stones, and urinary tract injury and infections, according to Healthgrades. Kidney failure; cystitis, which is a condition in which the urinary bladder swells; and prostatitis, a condition in which the prostate gland swells are other conditions that affect the urinary tract, possibly causing dark brown urine.
Some medical conditions including prostate cancer, copper poisoning and liver diseases, including cirrhosis and hepatitis, may result in dark brown urine by causing substance accumulation in the blood. Additionally, brown urine may be due to a life-threatening condition that necessitate immediate medical care such as rhabdomyolysis, acute hemolytic anemia and acute hepatitis. Certain medications such as antibiotics and laxatives, and foods such as fava beans, rhubarb and berries may also result in dark brown urine.