Took one Ativan this morning. Will it be out of my system on Thursday morning for a physical?

Not prescribed it, but a friend gave me a couple for anxiety. Will niacin help clear it out of my system in time for my physical on Thursday? And does MEPS search for ativan (benzodiazepine) in your system? I just need honest, reliable answers please, no bashing.

: http://alcoholdrugstreatment.info/took-one-ativan-this-morning-will-it-be-out-of-my-system-on-thursday-morning-for-a-physical