Why would methodone show up in a urine test if you havent taken it?

methadone is a synethic its has its own test to show it, but if you took a urine test and it came back positive and you didn't take methadone then i would have them run a gmcs test bc that will determine what came up as methadone, if you take benadyrl that would come up as a positive for methadone...hope this helps