The usual good sense from McGrath, of course and it really is important to take into account the different make up of different people. While I agree that makes sense, I have heard from various medics that heroin, for instance, is similar enough to some of the chemicals that the body produces naturally that it can trick the body into believing that it is necessary in ever increasing quantities. It is no wonder the stuff is lethally addictive for many people.
I wonder if the body is actually capable of producing alcohol in small quantities in certain cases? I believe it is a naturally occurring compound.