This was just one of many things I found on the net about false positives, hope it helps.
Opiate False Positives Back to Top
Poppy seeds, Emprin, Tylenol with codeine, Capital with codeine, Margesic, rifampicin, Vicodin, Percodan, Percocet, Wygesic.
Benzodiazepine False Positives Back to Top
Most prescription sleeping pills and anti-anxiety medication.