Answer:
if its in your system theirs no false positive.
Actually several drugs can cause false positives in different categories on a standard drug test...such as any ephedrine containing product can show up as a positive for meth, so if you have been using weight loss/energy pills containing ephedrine or perhaps an asthma drug containing ephedrine you may show positive for meth on your drug test. Basically, just be up front and tell the tester all of the OTC and prescription drugs you are taking and they will do further testing if necessary to rule out any street drug/illicit use.