Why did China attempt to control the opium trade? What was happening to their economy because of the British introduction of opium in China?

Opium trade was undertaken by Britain to overcome their trade imbalance with China. It created a steady market among Chinese addicts for opium imported by the West. It took the payment balance to run against China and in favor of Britain for the first time and opium addiction reached the official classes and imperial troops.

The Qing dynasty attempted to enforce restrictions over opium consumption through the Opium Wars, but China lost and the Qing's decline begun.