I recently tested positve for heroin even though I have never used it in my life. 2 days earlier I was at the dentist having some major medical work done. The drug test I had to take was a mouth swab test and I tested positive for monoacetylmorphine, a key ingredient in heroin. My level was a 23. Is it possible that something used at the dentist office caused this? If not, what else could have caused this? Like I said, I have NEVER used heroin.