Denied employment after drug test?

After receiving a job offer and ping the back round, physical test I on bad judgment failed my drug test. I suffer from migraine headaches probably 4-6 times a year "not frequent" and never asked for a prescription from my doctor. My Wife suffers from migraines much more frequent and has a proscription for Fioricet. I had a headache for a couple of days which turned out to be a migraine and she offered me one of her Fioricet s to help get rid of the migraine which I accepted as I have Done in the past "not on a regular basis" not thinking it would show up on my drug test as a narcotic drug. but for one Fioricet with no prescription I am going to loose a great opportunity for my Family. Bad judgment on my part but I am not by far a Drug user.