The resulting widespread addiction in China was causing serious social and economic disruption there. In spring 1839 the Chinese government confiscated and destroyed more than 20,000 chests of opium—some 1,400 tons of the drug—that were warehoused at Canton (Guangzhou) by British merchants.
The cost to China was enormous. The drug weakened a large percentage of the population (some estimate that 10 percent of the population regularly used opium by the late nineteenth century), and silver began to flow out of the country to pay for the opium.
hope this helps!