It actually depends on the type of drug test done on whether the ways to fool one will work or not. Most employers go the route of the cheaper tests so not to worry. Fdd was correct if it's been over 30 days you should be okay unless you did a huge amount.

Check out FAQ I belive it is under legal. There should be some stuff on drug tests there. It goes into detail. How to help pass it if you are concerned you might not. That kind of thing.