Hello!
As a result of the opium war and the Nanjing or Nanking treaty, China had to cede Hong Kong to the United Kingdom and accept the opening of ports in China so that the British can trade freely. China also had to pay about 21 million dollars to the British for the retention of opium and the costs of the war, as well as for debts that Chinese merchants had with British. The problem about the opium trade was something that was left aside in this treaty, because although it affected China it was beneficial for British trade. However, the opium trade was later legalized in the Treaty of Tianjin, signed after the Second Opium War.
I hope this can help you
