If they do need a drug screening see what kind it is before you get worried, a lot of companies now are doing this mouth swab test, its faster and cheaper than urine screenings but it only reads positive for weed and booze if you've had some in the past 3 days or so. Its really designed to pick up on hard drugs like crack and H not somthing as harmless as pot.
oh shit. i better stop smoking that rock.
safe to say.