Mummy, what's drugs?

[Phteven]

I put on Sunrise this morning because the house seems a bit quiet without DH rattling around.
The top story is Ben Cousins' drug dramas. Yasin listened for a bit and then asked "Mummy, what's drugs?"
Eeek, I thought I had a few years before I had to have this kind of discussion. I told him people take them to feel differant but they make you sick and he seemed happy with that but I feel it's kind of inadequate.
Does anyone have a better explanation?