Ask for a retest and have your scripts for any medications handy for review. The time to reveal any prescription or over the counter products is before a test. Your doctor should ALWAYS be informed of any pending drug test situations ASAP.
In these cases of a false positive I recommend people get a consult with an MRO. A Medical Review Officer is a doctor trained to say why something might have given you a false positive. You can find one in your area at aamro.com and look for the link that says "locate and MRO in your area". For the most part hair drug testing is very accurate, but maybe a med you are taking made it show a false positive. BTW, second hand smoke won't show up in a hair drug test.
Couldn't have said it better.