Rising from low levels in the 1840s,…

Rising from low levels in the 1840s, China produces 35,000 tons of raw opium in 1906-07-equivalent to 85 percent of world opium supply.

The reduction in British imports and Chinese suppression lead gradually to several negative developments: an increase in China's opium cultivation; a shift in consumption from domestic opium to imported heroin; and a centralization of criminal controls over the illicit opiates trade.
(Source: The Politics of Heroin: CIA Complicity in the Global Drug Trade)