A security clearance doesn't necessarily mean you have to take drug tests. You do fill out paperwork about your previous drug usage though.

> Then why is it classified? How separate is your branch from the weapons branch, that you acknowledge exists?

There's a lot of dual-use stuff that's not used for military applications but could be by another actor. Dual-use means that it could be used for civilian and military applications, not that it actually is.

So if I build a revolutionary weather radar that could be used for military reconnaissance by Iran if the technology came out, but the US military isn't interested because they already have something better, it would be completely civilian but classified.