Here is a simple solution. I'm sure that they asked you if you are on any medications. If they do detect, and I'm fairly sure they won't. Tell them you've had a cough and took a cough med right before coming in. Look at the over the counters and find one with alcohol, use that brand, but make sure it has alcohol. The tests I've seen, they test against another positive, that positive is usually high, so they will get a good positive reading. So, in my opinion, you will test negative. If they ask if why you didn't tell about the cough med before, tell them you thought that they were talking about presciption meds and you were nervous. Good luck.