Never, and I never plan to. Unless we’re counting the stuff steve mentioned. Even those, though, I try not to take unless I feel it’s really necessary. This is just my personal stance, not something I’d push on anyone else, but I look at drugs and alcohol as the laziest, least productive possible solution to a problem. (In the case of alcohol and recreational drugs, problem = boredom. Or a reality one currently finds displeasing.) Something that should only be resorted to when no other solution will work. Whenever possible, I deal with problems by working through them, and/or devising solutions to them, and in doing so, improve my ability to work through them in the future. An instantaneous solution like drugs is a quick fix one can easily become dependent upon, and it doesn’t solve problems, it only stops you from noticing them. That’s not the way I do things.
Of course, like I said, it’s just my personal stance. I really don’t have any problem with other people doing whatever they want...which is why I get irritated when I’m talking to someone, and the subject of drinking comes up, and I casually mention that no, I don’t really care for it, and they look at me like I’m from another planet. And go... “Why not?!!!”
And, all of that said, I do think pot should be legal. As I see it, it is responsible for far fewer problems than alcohol, and alcohol is legal. And it’s not like the fact that it’s illegal is stopping anyone from doing it. If anything, it’s probably an incentive for some people to do it.