Pot messes up time recognition and memory so would you like a pot head to be doing your blood work at a lab? I wouldn't. The stuff stays in your system for a month and it isn't like alcohol that you sleep off and go to work in the morning. There's a good reason there are checks at the nuke plants and the technology is so sensitive you will test positive for heroin if you have a morning poppy seed bagel on the way to work. There's a spray for your hands to test for coke also. Not used much anymore because of the contamination of money when used to snort coke.