Linking back to the germ of this idea, here.
Considering the discourse that surrounds recreational substance prohibition, and its overlap with organised crime. I'm looking at a historical perspective to get the background - I suspect that language, particularly from journalists, has been a fundamental aspect of this phenomenon.
We can trace prohibition back to the 19th Century, arising out of UK imperialist and economic motives in relation to China and the opium trade. The punitive colour arose from DORA during the FWW, (that last link is to a chronology supplied by RELEASE, which has an unfortunate omission and resulting ambiguity: it refers to the first and second Opium Conferences at The Hague in 1911/12, but omits any reference to the confusingly identically named conferences which took place in Geneva in 1924/25).
With the Great War over, The Dangerous Drugs Act 1920 formalised the situation and followed on from The Hague conference. The hullaballoo following the death of Billie Carleton may have played a role, too.
In 1926 the Rolleston Report introduced a therapeutic aspect. The Dangerous Drugs Act was amended in 1928, to incorporate the UK's obligations under the Geneva conference of 1925, (the people in the photo are the League of Nations' Opium Secretariat). Kendell gives an account of the 1925 conference in Geneva.
There is a lighthearted article by Mills. (Coincidentally, that author is, or was, at Strathclyde).
Hansard provides some insight. There doesn't seem to have been any kind of debate when the the law was amended after Geneva to include cannabis in the category of poisons. The only mentions, on 2nd April 1925 (so just a few weeks after Geneva), are three MPs asking the Home Secretary to delay the change in the law because of the hardship it would cause to "many small shopkeepers, who are not members of the Pharmaceutical society, who stock articles, such as corn plasters, containing a small quantity of cannabis indica". Corn plasters?
On the same day there was a reference to the conference, and the setting up of a "central board", in a question to the Home Secretary from a Mr Forrest, who had also been one of the MPs who had taken up the case of the cannabis-selling shopkeepers, together with Walter Womersley, and Herbert Williams.
The next mention of cannabis indica is in the Lords, in December 1929, from the noble lips of Lord Russel, Under-Secretary of State for India, no less, going beyond his portfolio somewhat in introducing the Road Traffic Bill, (he was a motoring enthusiast, apparently). Clause 14, he tells us, "is a very valuable clause dealing with drunkenness" - valuable because it introduces the phrase under the influence of drink or drugs. He refers to a case in The Times that week. You need to pay to get the full record, but the search result tell us it involved a Dr James Glasgow Bell, of Foleshill, a suburb of Coventry. The Coventry Police Court had to acquit him on a driving charge because he wasn't drunk, apparently, but stoned-as-a-bastard.
[not fully referenced - follow links]
Kendell, R. E. (2003) Cannabis condemned: the proscription of Indian hemp. Addiction, 98, 143–151
Mills, J 2002 Poisons, the police and the Pharmaceutical Society: cannabis and the law in the 1920s Pharmaceutical Journal VOL 269; ISSU 7229 896-898