Random drug and alcohol testing by the CAD is on the way apparently.
As for the drugs - I would exercise extreme caution. I was taking Tamazepam when on extended ops in the RAF. After finding one wouldn't work after a while, I started taking two. After two didn't work - I stopped.
Stilnox/Zolpidem is popular among our peers, but is also highly addictive. A non flying friend became dependant on them for sleep after taking them for only a few weeks. It seriously affected her health, to the point that if she had been a pilot, she would probably have lost her medical.
Stilnox is apparently available from pharmasists in Mongkok without prescription. However, I have heard of people spending a lot of money on these just to find they're fakes!