Late reply:
I've seen off-label pill use, marijuana, and cocaine at work related events (or just casually around the office) in at least 5 states, ranging between the West Coast, the East Coast, and Texas. The settings have ranged from small companies and start-ups (which have the most drug use openly) to large corporations like Microsoft (where people at least hid in the bathroom or private areas while doing lines). Marijuana is the most prevalent that I've seen, at 8 different states and between widely varying social groups.
I've even been offered ADHD meds not prescribed for me by senior people at the company I worked for at the time, to keep me working long hours and more focused at work. (Hey, if it works for college kids, it works for adults.)
The simple answer is that not everyone agrees with laws against vices, particularly things like prostitutes and drug use - and see no reason to follow them.
If you're not aware that things like this happen, you probably give off the impression that you'll try to get people arrested and seriously damage their lives because they take an intoxicant you were told was bad, rather than alcohol or any of the various other legal ones.
tl;dr: It's all over, and if you don't see it, people are actively hiding it for you because they don't trust you to make reasonable choices.