Will an otc user flunk a drug test?

Not usually: It depends, some apparently innocent otc contain ephedra derivatives or codeine; also, false positives for some meds (tca, barbiturates) due to benadryl, (diphenhydramine) ibuprofen, naproxene and others are common. Drs are aware, generally. But usually with the most common methods, hardly ever any otc will affect the main ones (cocaine, bzd, thc, amphetamines, etc). Ask your dr. Stay clean; good luck.