I have had a really bad experience with random drug testing at work. The only illegal drug I have ever done was marijuana years ago, and only two or three times at that. I don't even drink since I am allergic to alcohol. However, I tested postive for cocaine---which I had never done. When I asked for a retest, they denied it, stating that by the time they retested me it would be out of my system anyhow. Eventually they gave me the benefit of the doubt, but I lost out on promotions after that and was treated with disdain. These tests often create false positives and yet, there is little we can do about it. We are guilty until proven innocent. It is definately not true that if you are innocent you have nothing to worry about. Protect yourself and detox.
The best ways, according to the internet, to beat a drug test are the cranberry and water mixes, and definitely the vitamin B supplements. But from what I read, do not take the B vitamins the night before or the day of the test, since this sends a red flag that you were trying to detox. The water won't matter in terms of how it looks .... since you can always just claim you are trying to lose weight
Also, apparently taking a tylenol or aspirin or something with a reasonable dose within a few hours creates inconclusive results.
I read on Ehow, I think it was, that if it is a saliva test they are the easiest to beat. Use listerine and altoids right before, again it interferes with the results.