Warfarin prolongs the clotting time of blood. People on warfarin therapy undergo regular blood testing in order to establish the clotting time of their blood and the warfarin dosage is adjusted accordingly. Alcohol does interact with warfarin and can result in extending the clotting time. Therefore it is recommended that people abstain from alcohol while taking warfarin. Warfarin also interacts with aspirin and many other anti-inflammatory drugs. It also interacts with some of the oral drugs used in the management of diabetes. Cimetidine also interacts with warfarin. As a general rule it is best not to take any over the counter medication while on warfarin unless the matter has already been discussed with the GP. The principal side effects of warfarin relate to its mode of action therefore some people may experience bruising, purpura or frank bleeding. Regular blood testing guards against these possibilities. Blood testing can usually be performed on a monthly basis once the optimum dosage has been established for each individual patient.