Excuseable reasons for failing drug test?

Typically a drug test can tell you which drug came up positive, it is unlikely that most will coorelate with an over-the-counter cold medicine but if it did they may give them the benefit of the doubt. WHen I worked for an Addiction Treatment Service we instructed all clients that were required to Pbt (blow in tube for alcohol level) to abstain from ALL medications and if they needed to take ANYTHING they had to get approval and produce the bottle and take it in front of personell. Drugs are different than alcohol in that they are not found in many day to day products so it is even less likely that a "dirty" test were to come from cold medicine.