Well, as Roger mentioned, drugs and alcohol tend to be rather rough on the voice. That makes them a pretty bad idea for anyone who wants to sing right off.
I haven't noticed that drugs tend to enhance anyone's creativity, either. Like others have noted, people on drugs seem to have a lot going on in their heads, but can't do much with it. Certainly, there are lots of artists who have been on various substances and produced wonderful work. Creative people will be creative; drugs will not stop them from being so, though they might inhibit said persons' ability to process their creativity. Drugs will also not make un-creative people creative.