My dad insists that there weren't any "illegal" drugs (opium, weed, etc) or prostitutes in the early days after the communists gained control in China (think 50s-60s). I insisted that this is ridiculous but then realized that I am having a hard time finding sources about these subjects that aren't from the Chinese government. Can anyone help me out?
Maurice Mesiner's "Mao's China and After" definitely agrees that opium use, prostitution and gangster-ism was all but quashed under the newly formed communist government. I'll leave the "how" to someone more knowledgeable than myself - but at least one historian agrees with your father.
Edit: nearly > newly
Did your dad live in China in the early 50s? Because his memories in and of themselves would be pretty interesting, even though a proper answer to your question from a historian would be interesting too.
In the conclusion to Frank Dikotter's "Narcotic Culture: A History of Drugs in China" he states that the communist party had eliminated all illegal substances by 1952. Earlier in the book he argues that opium/opiate usage specifically had declined on its own throughout the 1930's and 1940's. The basic thesis of the book is that the demand side of drug use is most important. Government policies to suppress drug use and trade are ineffective or harmful.
He even compares drugs to prostitutes in talking about the communists' effective suppression of "these symbols of capitalist decadence".