The only drug test that can show results across a wide span of time is taken from a hair sample..
This is the reason why, in some cases, an attorney will have their client shave their hair.. not a fashion statement but a legal tactic.
The same sort of reasoning was in play in the old VHS tape days... substances in the air got wound into the tape as it moved from reel to reel. You can run it through a rewinder with a slightly dampened cloth clamped over the tape, it cleans the tape and leaves the residue on the cloth and the residue contains microscopic debris from the moments it wound through the machine and was exposed to the air.
They would always gather up the tapes from a crime scene.. this is one of the reasons why.
Saw of picture of Brad Pitt with a shaved head last week. Not a good look on him. You're making me think that drug testing could be a condition of a movie role contract!