Cocaine and some of its metabolites - substances to which cocaine is broken down in the body will appear in your blood and urine for few days after you have received the drug. Tests for possible drug use will then be ``positive'' for cocaine. If you must have such a test within 5 days or so after receiving cocaine, be sure to tell the person in charge that you have recently received cocaine for medical reasons. It may be helpful to have written information from your family doctor stating why the drug was using, the date on which you received it and the amount you received.