Why did Britain sell Indian opium in China?

Britain sold Indian opium in China primarily to resolve a chronic trade imbalance between the two nations. During the 18th and 19th centuries, there was a massive demand in Europe for Chinese luxury goods—specifically tea, silk, and porcelain—but there was very little demand in China for European manufactured goods. Consequently, European traders were forced to pay for these Chinese products using gold or silver.1

To rectify this, the British East India Company established a monopoly on opium cultivation in the Indian province of Bengal. By exporting this opium to China, the British created a steady demand among Chinese addicts, which allowed them to earn the currency necessary to purchase Chinese goods without depleting their reserves of gold and silver.123

This trade was conducted illegally, as the Qing dynasty had outlawed the importation and cultivation of opium in 1796 due to the severe social and economic disruption caused by widespread addiction. The British East India Company facilitated this by licensing private "country traders" to smuggle the drug into China, effectively using the profits to finance their commercial interests.123