Urea in the human body is produced in the liver, using its system of enzymes and carrier molecules to convert highly toxic ammonia and carbon dioxide into urea. This can then be safely removed from the body by the kidneys.
Urea is the major end product of nitrogen metabolism in humans and mammals. Urea, while not as toxic as ammonia, cannot be tolerated by the body in large amounts. Problems with the urea cycle can quickly become fatal. Liver cirrhosis, which can be caused by alcoholism, can create an interference in the enzymes which produce carbamyl phosphate in the first step on the cycle.