I was introduced to daily caffeine usage by the most religious christian engineer I worked with at the time. We would drink 2 cups at once to get a jolt.
I don't think I need to ask about engineering, as many of my coworkers have 4+ cups of coffee a day. I can't imagine how many of them take other stimulants/anti-depressants, etc...
From professionals to laborers, why would we assume drug usage is any different?