Close the borders...execute drug dealers on the spot!
Oddly enough, that along with a one strike and you're out program to help addicts get off of opium is exactly what worked for Mao in China.
For all the talk about "who lost China", China was "lost" to the US when Mao found out the US wasn't dismissing his telling us Chang was in the opium trade, but that we actually knew all along about Chang kai-shek & his inner circle being heavily involved in the opium trade.