THC is a chemical that enables deep thought. Fair enough this may be at the expense of other brain functions but I don't believe that it makes us less capable to think. The most profound thoughts you'll ever have enter your head when you are high on THC. You focus your energy more on the act of thinking. Look at Stephen Hawking, before he was dis-abled he was just an average physicist, now he is one of the most prominent astro-physicists in the world. His dis-ability has just made him concentrate more on thinking, This is very similar to the way THC works. It disables parts of your brain so that you can concentrate more on using the other parts.

Also the cells in our bodies are constantly dying and being replaced. Scientists aren't sure whether after prolonged drug use the cells are replaced. The best thing to do is keep your mind active, puzzles or my personal favourite chess. Reading is excellent, whether it be fact or fiction. I always play chess while stoned, the game doesn't interest me hardly at all when I'm sober.

Most of the greatest writers throughout time were drug users. Even George Orwell had a heavy addiction to nicotine. To say that drugs destroy your brain, I feel is untrue. If you keep your mind active no harm should befall it.