This movie is often wrongly believed to have been made by the US government. It wasn't...it was an exploitation movie, which sought to make money off the moral panic surrounding marijuana without breaking the Hays code.
It is, nonetheless, compulsory viewing for anyone interested in the processes by which the drug war establishment generated the current orthodoxy of beliefs regarding the extreme hazards of drugs such as cannabis. It is interesting to see the Reefer Madness themes re-emerging in Britain recently too, with certain scientists speaking of causal links between cannabis and schizophrenia. While the regular use of any psychoactive drugs by the very young or the mentally confused & distressed is not recommended, the fears around cannabis are undoubtedly derived from broader and more complex zones of the social landscape.