Thank god they didn't check my blood for drugs it would have looked like a dead concert in the late 60's early 70's. Turns out they check your blood for over all health and to get a base before you start the job. They will randomly check your blood and or hair to make sure you haven't been exposed to anything. Thats on top of the yearly blood work and physical. I can see one of the people telling me about my blood work I smoked 3-10 joints a day for the last year.