"Narcotics police began to shut down this loophole, state by state, actually rounding up 17,000 doctors nationally between the mid-1920s and the mid-1930s. In California, the success of the legal drugs program was so clear that many people fought back; the mayor of Los Angeles was one of its strongest defenders. But the feds came for California's legal drug program too, and in the early 1930s Edward Smith Williams was arrested.
"The reasons for this crackdown only became public years later, when they were established in a trial.
"The head of the Narcotics Bureau in California in the 1930s, Chris Hanson, was approached one day by a local drug lord called Woo Sing. He pointed out that in states like Nevada, where the legal clinics had already been closed, addicts were forced to go to dealers; and he was furious that in California, the gangs couldn't find customers because users and addicts could buy their drugs legally. So Woo bribed Hanson to introduce the drug war into California. Hanson was convicted of taking bribes–but the war on drugs he brought to California continues."
Johann Hari in the Los Angeles Times explores the origin of the war on drugs in California.