Keep in mind that it came into being right as the Nixon years used anti-drug legislation to effectively take down blacks and hippies.
On top of that you have nations that wanted to hedge around their big and growing pharma industries, and others that was negative to all drugs (except their local cultural ones) for religious and cultural reasons.
In effect religion and economics trumped medical science, and the world has been dealing with the blowback ever since.
https://en.wikipedia.org/wiki/Single_Convention_on_Narcotic_...
Keep in mind that it came into being right as the Nixon years used anti-drug legislation to effectively take down blacks and hippies.
On top of that you have nations that wanted to hedge around their big and growing pharma industries, and others that was negative to all drugs (except their local cultural ones) for religious and cultural reasons.
In effect religion and economics trumped medical science, and the world has been dealing with the blowback ever since.