Drug tests work on the principle that whatever we take into our body is broken down and absorbed by our system. So you can be pretty sure that what goes out of our system contains a history of what has been in it. As our body breaks down everything that we eat, drink, and inhale - including prohibited substances, of course - metabolites are formed as part of this complex process. During drug testing or screening, a kit will be able to determine what kinds of substances are present in or absent from our system. Therefore it is imperative that you learn about how to pass a drug test.