A) you can say you had a headache and that was what was in the med bottle that your roommate forgot to tell you was where she put them when she was thought she was going out of town instead of taking her whole prescription bottle. B) completely BAD idea to be taking medicine that you don't have a script for and it's actually illegal because there can be a lot of side effects that can harm you as they wouldn't do to someone else. This isn't like taking an over the counter high caffeine stimulant (you could say you had 3 red bulls that morning which is very unusual for you but you wanted to be very alert for the interview and also started a new vitamin regime that contains taurine and inositol so say you have no idea how the 'amine' could be showing up unless it's due to the new compound of crap you consumed that morning--say that morning because that validates the level if it shows up--and finally be willing and ready and vyvanse free so if they call with any concerns you can say one of those excuses above and follow it up with you are willing to go that same day and retest at your expense. But for real---don't take someone else's meds---get your own if it's advised you need it. The caffeine and other OTC stuff has really come a long way but does cause the heart to race and make you seem a bit on the whacked and hyper side but if that's what you need til you can with a doctor then, that's just how it has to go if you don't want to mess up a job opportunity. good luck.