China, too, have a far lower drug use rate. Not sure for Japan and Hk, but for China I think there are two main reasons. One, she was "locked in turmoil" during the 70s and the 80s, so did not get the influence from this period. Two, most young people are busy making their life, and have actually good hope to have a much better life than their parents (which is not that difficult).
China has a problem with Ketamine addiction, not helped by whole villages that mass produce the drug. There was a good documentary about this: https://www.youtube.com/watch?v=vxXvTi3QRwA
China certainly has drug problems, but it is not like in West: i'd have to search carefully to find one French guy of my generation or below that never tried hash. In China most Chinese I know never tried. It's just not the fashion yet. Only a very thin slice of the society is in contact with drugs.
