In my sunday school class, one of the kids asked about why people use drugs. I was caught a little off guard but my short answer was that people want to feel good. Which is accurate. Personally, I think it is better to be honest with kids as they will find out soon enough anyway. But upon thinking of this question I came up with a better answer.
People are looking for something big in their lives. They want to experience something grand and venture into the mysterious. Without God in their lives, they have to find a substitute. They end up settling for all sorts of things, including addictive, destructive, and dangerous drugs.
We need something big in our lives. Something powerful and eternal. We were designed to worship and be in awe of Someone who is so much more than we are. When that need is not getting filled legitimately, we fill it with junk that never satisfies. People use drugs because they are missing God in their lives.