I've heard of the cases where the poppy seeds caused positive opium results. Also some cold and allergy meds with interfere with amphetamines. The most disturbing thing is when people are fired for coming up positive for something they have a prescription for. I know for a fact this has happened. Some people will tell you this can be challenged in court. Don't believe it. It just depends on where you live. They seem to be able to get away with whatever they want. It's a crapshoot. Oh sure, I fell for it at first too, I thought the chain of custody procedure would protect people. The fact is, drug testing has become an industry in itself. Small companies are not even required to use certified labs! The whole thing has gotten out of control! My neighbors son was tested after he got a new job and they said his urine showed nicotine! Since he put down he was a non-smoker they questioned him about it. He said he had just gotten married and smoked a cigar, which was the truth. I didn't know places tested for that! It's getting to where every facet of our life is monitored, for our own good, just like that book, brave new world, or was it 1994, you get the idea.