I would say go the video game/television rating way of it. It's okay to reference or mention drugs, and show the use of legal drugs like tobacco (with recent changes to it, I would say marijuana could be classified the same way as tobacco; it's definitely not as taboo anymore) - but if you're showing the use of hard, illegal drugs like heroin, cocaine, meth, etc. then yes, best to put it behind a NSFW filter, or dismiss the filter and not show them being done (ex. there are shows where characters are obviously doing drugs, but they don't show the actual act onscreen so they can keep it a certain rating).