What will make fail a drug test for pot?

I got a drug test back a couple years ago that came up positive for amphetamines. I was confused, asking if there was a mistake made durig the test or perhaps a accidental switch of my sample with someone elses. They assured me everything went as scheduled so I did some research and found out why I came up positive for amphetamines when I had never done it, been anywhere near others doing it, as a matter of fact, aside from what I had been told in school, I knew nothing about the drug.

I found a product that I used frequently to clear my sinuses after Surfing called AFRIN to be the likely culprit. It is administered in the form of liquid mist and sprayed into and up the nostrils. AFRIN contains amphetamine based chemicals that when tested less that 12 hour after using are enough to trip off the sensitive modern day drug screens.