How was tea connected to the opium trade and the opium war of 1839-1842?

China was a big exporter of silk and tea. It was exchanged for gold and precious metals. However, China kept its markets closed for the British which made trade a one-way road. The British didn't accept this situation and it leads to war. The Chinese lost the war and were forced to have free trade ports (Treaty Ports) with the British. It was called the opium war because it was the drug of choice for many Chinese people. It was something the British imported into China. Not that the Chinese used a lot of drugs. Raw opium has a relaxing effect (similar to a few drinks). It can't be compared to opium derivates like morphine and heroine.