There is a stoners’ parlour game that imagines a parallel society where marijuana is the dominant legal drug of choice and alcohol the sideshow. In the land of Mary Jane it generally ends with Donald Trump not being elected US president.

Weed kicked off the global War on Drugs with the US enactment of the 1937 Marihuana Tax Act (sic). The 1961 UN Single Convention on Narcotic Drugs declared Cannabis sativa “evil”. Former US president Ronald Reagan’s drug czar, Carlton Turner, scapegoated marijuana in the 1980s for “the present young-adult generation’s involvement in anti-military, anti-nuclear power, anti-big business, anti-authority demonstrations”.

The US wanted the plant’s global root-and-branch eradication, indulging in foreign drug wars and the liberal use of the Vietnam War’s Agent Orange defoliant on its client states’ illicit plantations...