In the late 18th century, the English East India Company was buying tea and silk from China for sale in England. As tea became a popular English drink the tea import increased largely. But this created a problem. England at that time produced nothing that could be sold in China. Buying tea with silver coin created loss of treasure from Britain.
The Britisher searched a commodity which they could sell in China. Opium was such a commodity. The Chinese were aware of the dangers of opium addiction. The Emperor of China had forbidden its production and sale except for medicinal purpose.
But European merchants began an illegal trade in opium. When the British conquered Bengal, they made a determined effort to produce opium in Bengal. Unwilling cultivators were made to produce opium through a system of advances. Large number of poor peasants of Bengal and Bihar started to produce opium. They got very low prices for their product.
By 1773, the British government in Bengal had established a monopoly to trade in opium. As China became a country of opium addicts, British trade in tea flourished. The returns from opium sale financed the tea purchases in China.
Thus, the history of opium production in India can be linked up with the story of British trade with China.