I have been taking 4-6 10/325 Hydrocodone tabletsper day for several years. On my last visit to the pain specialist, I was asked to take a urine test to insure I was actually taking the drug, which I readilu agreed to. However, I'm now told that the drug did not show up in the test and was refuse my last refill. What could cause this fals negative? Could other meds I take have any effect on this?