I couldn't find a definitive answer anywhere, but on my layover in Canada I asked the dude at the pharmacy in the airport what the best over the counter stuff was for headaches and he gave me some tylenol with codeine. Do they test for drugs at the physical exam? The lady from the school helping me out said they "check your peepee", whatever that means. I feel retarded for not realizing till now codeine tests positive for opiates.