The british traded opium from for chinese-manufactured goods and tea.
india, spain, japan, germany.

The Opium was from India and they use it to pay for the goods they bought at Canton that Chinese will accept instead of silver. At that time, Opium was a medicine with a high value as it was know to kill pain, was use as a sleeping medicine and stress reliever. However, it was not good as it was addictive and millions of chinese were dependent and addicted to it.