The answer is Britain agreed to stop importing opium beginning in 1845
This is because
With The Treaty of Nanjing on August 28, 1842, also known as the First Unequal Treaty, China acknowledged that it lost the war, and
was forced to pay compensation in large amounts. Some of the sanctions imposed on China were as follows:
Hong Kong would be handed over to England to allow the settlement and trade of the British; five ports, namely Guangzhou, Amoy, Fuzhou, Ningbo and Shanghai ports, would be opened to trade with Europe;
British citizens would be granted extraterritorial rights so that the British accused in China would be tried in the UK courts.
