Quite possible that if you take a cocktail of drugs you end up completely out of it and unable to control yourself. But it's no defence.
Prevent anyone on drugs from entering the BTS station? You want security officers on every entrance, stairs, escalators and lifts? And they need to be testing people to see if they're on drugs? Could work, but it would cost a lot and make travel almost impossible. (Where do some people get these ideas?)