It would be pretty dumb to go to your program director w/o knowing a) what you sent was a UDS (although it most likely was unless he wanted to make sure you weren't pregnant, had a UTI, some weird nephropathy, in DKA, or other a bazillion other things he wouln't care about) and b) whether or not it will be positive for cannaniboids. like i said, it depends on when and how much. and if it does turn out positive, here are some excuses
1) i just wanted to make sure i was getting the best stuff for my grandpa w/ glaucoma
2) i went to a dave matthews band concert a week ago and i thought the air smelled weird
3)my hippie aunt sent me a care package with some of her special brownies, now i know why they made me hungry.
as far as grounds for dimissal, i don't know.
disclaimer: i do not advocate the use of any illicit substances, the above excuses were merely pulled out of my rear. they have never been used in any situation to get out of dismissal from elementary, middle, junior, or high school or any other academic institution