Partly as a response to the 1937 Marihuana Tax Act in the United States, Jamaica increases its penalties for cannabis possession, sale and cultivation. For the first time, mandatory imprisonment is laid as a possible penalty. Other factors that played a role in the implementation of these stricter penalties include the economic depression Jamaica was going through at the time as well as the Rastafarian-associated conflicts in the country.
Source: Austin, G. A. et al. (1979). Perspectives on the history of psychoactive substance use. NIDA.