The classification system here is redundant and needs reforming, like in most other nations, I expect. Just for a few examples...benzohs are usually the lowest class (C). And we all know the tolerance and withdrawal from them. Special mushrooms (which I've never tried, never will) which are completely safe if used properly, Class A. It's not rated by harm whatsoever. There does seem to be a link to what's available to prescribe and what's not...
I might have gone off on a bit of a tangeant, sorry...was just saying how ludicrous the classification systems are, but to keep on topic slightly...for me, tr@m is way more dangerous than other weak op8s (cod, DehC), yet it's often classified lower. It's all just topsy turvy.
Like PTFC said, google will be way more reliable than me, but just thought I'd come along and ramble a bit.