I know exactly what you mean. That is how I was in the first part of highschool. Pot and somewhat alcohol allowed me to be social. It wasn't even really being high, it was the comfort of knowing how to interact with people (watching half-baked, listening to Pink Floyd, etc.)
But like you I came to realize that I neglected other parts of my life. Again, I don't have that much of a social life anymore, but I am really much happier than I was. I really enjoy going for long walks by myself, reading, watching movies (indie and foreign) as well as many other things. I don't have as many friends, but I am still friends with my real friends, and have found other ways to interact socially.
When I do go to a party or bar, or something like that, I do for the most part have a good time, but I usually leave feeling drained and depressed, and I regret the fact that I could have been watching an Ingmar Bergman film and reading a classic, but instead got drunk.
I don't know if any of that made sense. I would suggest really throwing yourself into your hobbies. I don't know where you live, but finding a writting group, or a band would give you something to not only stay busy, but also focused, which should hopefully reduce your desire to do drugs, while also being social.