I am a Chinese, so please bear with my English. I studied this history entirely in Chinese.

The most famous policy to solve the opium addiction epidemic would be the "Destruction of Opium at Humen", also known as 虎门销烟, directed by the Imperial Commissioner of Qing Dynasty Lin ZeXu (清朝钦差大臣 — 林则徐).

By the 31st of December of year 1838, Emperor Dao Guang has announced that usage of opium is banned nationwide. However that was not effective. At the same day, the Emperor also appointed Lin ZeXu as the Imperial Commissioner of Qing Dynasty mainly focus on how to save the Qing Dynasty from nationwide opium addiction.

Basically what he did is that he confiscated and destroyed 19,187 crates, 2119 bags, and approximately 2.3 million 斤 (idk the name of measurement this in English is catty) of opium between 3rd of June 1839, to same year 25th of June.

Soon after that incident, the First Opium War has started, and I don't have any source about the solution to opium addiction after the First Opium War started.

Notice that I use Qing Dynasty, it is to clarify that I'm talking about Qing Dynasty only. Republic of China didn't appear until year 1912, which is almost a 100 years from the "Destruction of Opium at Humen" incident

Source: 《晚清巨人傳·林則徐》 ISBN 7-80557-894-X 、 《林則徐——中國近代化的先驅》 ISBN 957-530-008-4

Side note: Opium addiction was the main reason that Chinese was called "Sick man of the West East" (东亚病夫) by that Era.

(Sry mods, can't find English source, hope Chinese source is sufficient)

Edit: After doing some quick confirmation, 斤 in English is Catty. However from catty to gram. differs from region to region. In PRC, 1 catty = 500 gram; In ROC, 1 catty = 600 grams; In Singapore and Malaysia, 1 catty = 604.8 grams.

I have no idea which conversation is the author using, so I'll leave the 斤 there.

Edit2: mixed up east and west.

Everyone knows that Japan invaded China in the 1930s and 1940s. However, many people didn't know that both the Kuomintang-Communist and Japanese invaders actively traded with each other, especially opium.

Opium was an extremely widespread crop in China. After the Taiping Rebellion in the 1850s, many businesses switched to opium as an alternate currency. Both the Chinese (including the Qing Empire) and Japanese used opium sales and trade to increase fluidity and tax revenue.

However, once the Communists came out on top of the Chinese Civil War, there were literally millions of opium addicts. The CPC utilized incentives for farmers to replace their profitable opium crops with food crops. There were, of course, community 'education' programmes to educate the population. Of course, secret police and brute force were also likely used.

You have to remember that opium in China, although widespread, was mainly tied to the 'gangster' criminal organizations, especially in Shanghai and other port cities. The Communist government cracked down abd essentially squashed major organized crime groups, limiting the supply and flow of opium.

I recommend 'Mao's China and After' by Mesiner. Be careful when looking online about this topic, as many of the top hits on Google are ridiculously biased.

Followup question : Did opium production cease when the British left India?

I don't really post much, so sorry in advance for the bad formatting.

Hi, since I didn't see that much related to the opium trade and its eradication under the Communist Party, I'll try to chip in a bit here. Most of my information comes from an edited volume by Timothy Brook and Bob Wakabayashi, titled "Opium Regimes: China, Britain, and Japan, 1839-1952." It's an excellent read if you're interested further in the topic.

During the Communists' struggle with the KMT before their ascension to power in the postwar world, they actually centralized control over the opium trade in their area of control (the Shaan-Gan-Ning area) and sold it at a profit to areas outside their control. They then relied on the profits made off of the opium trade to fund the development of the Shaan-Gan-Ning area. The opium trade was actually a critical source of funding for them before WWII and the civil war with the KMT.

Moving forward, after they took power, the CCP actually used the eradication of opium as a method of consolidating their hold on power. Wiping out opium was a critical part of the CCP's state building process. By stamping out opium, something that previous regimes (the KMT, the Qing) had disastrously failed to do, the CCP helped strengthen the legitimacy of their nascent regime. The really interesting part of this is how they managed to wipe out the drug. Bin Wong and Zhou Yongming discuss at length the techniques used in the anti-opium campaigns of the 1950s, but I'll summarize a few here to give you a quick idea.

Anti-opium campaigns in the 50's were often these sort of mass rallies and public trials of opium addicts. At what were often trials by public opinion, cadres would whip the crowd into a frenzy against the unfortunate addict or addicts on trial. The trials valorized the group by a collective infliction of justice against the wretched addicts. Similar to how opium isolates the addict from the world, separate from their social reality, the trials and crowds isolated the accused.

The reason I expanded a little on the communal nature of the campaigns is that I believe it helps shed some light on how influential the political context was to eradicating the drug. Specifically I'd like to use these two examples to push back a bit against arguments that the negative social connotations attached to opium smoking were the primary reason for its near eradication under the CCP. While these negative connotations played a part, they most certainly do not tell the whole story. The social and political contexts of the eras played just as much of a role. In the pre-war era the KMT's anti-opium efforts were frustrated by the CCP's centralized control of opium trafficking, while in the post-war era the Party devoted its full attention to mass rallies and anti-drug campaigns as a crucial method of consolidating their hold on power.

Anyway, sorry that got a bit long, but hope it provides a bit more information on a really interesting topic.

Sources:

1. Zhou Yongming, “Nationalism, Identity, and State Building: The Anti-Drug Crusade in the People’s Republic, 1949-1952,” in Timothy Brook and Bob Wakabayashi eds., Opium Regimes: China, Britain, and Japan, 1839-1952, Berkeley and Los Angeles: University of California Press, 2000.

2.Chen Yung-Fa, “The Blooming Poppy Under the Red Sun: The Yan’nan Way and the Opium Trade,” in Timothy Brook and Bob Wakabayashi eds., Opium Regimes: China, Britain, and Japan, 1839-1952, Berkeley and Los Angeles: University of California Press, 2000.

Mods, let me know if I should put match the sources more to the text, i.e. footnote style.