cough a lot !!!!!!!!!!!!!!!!!!!!! but make sure of a couple things:

A. That you dont sound like a retarded bird when you do it. And also dont act like you have a cold, as it is a COUGH suppressant, not pseudophedrine (aka Sudafed TM).

B. DOnt cough Too loud, and too much. Just do it briefly andkind of try to make your face look pale and sick (I am good at acting; many trips to the nurses offics ).

C. Don't wear anything suspicious either, if you're wearing stuff that makes you look like a stoner, they'll card you obviously. So I suggest wearing something appropriate.

D. If they do card you, DO NOT PANIC! The worst thing you can do is argue with the personnel of the store. Do not looked miffed, or paranoid, or shocked, they will probably just not give it to you.

E. Try to keep your face straight, as if you were buying medicine seriously, If you keep looking sick when they ID you and you just say "I left it at home", and keep acting serious, keeping it cool, acting sick, they may cut you slack.

F. If they do ID you, again don't panic, just simply ask why (dont make it into an argument). She will probably say y'know the usual. Then ASK her for an alternative medicine for cough. He or she will help you.

Hope your a good actor