Reefer Madness, the movie, came out just as Prohibition was about to be repealed, cutting into the profits of bootleggers, the job opportunity for enforcement agents, and the “spiritual” profits to be made by radio evangelists and other crusaders (the last group actually got a BOOST, as it turned out). While government-paid doctors and evangelical crusaders had the movie produced, the other groups mentioned obviously aided, if only passively, this effort to arouse panic.
Ironically, the teenagers in the 1930’s who were portrayed as loving pot so much lost interest in it after an initial fad; it was not until three decades later that it took off in the mainstream of society. Opiates such as heroin got most of the attention of post-Prohibition law enforcement (and produced most of the profit, although in a much smaller market, for post-Prohibition gangsters), and they were definitely NOT mainstream drugs. Then LSD came along, and pot as an easier to obtain “LSD lite.”