The statement that Russians supplied the Chinese with opium is completely without foundation. In the mid-1680's, Sofia Alexeevna, the regent for the boy Tsars, Ivan and Petr, agreed to make war on the Turks by attacking their proxies, the Crimean Tatars. As a consequence, she sent agents to negotiate a settlement with the Qing dynasty over the dispute about the Amur river valley. There was virtually no contact between Russia and China from 1689 until the mid-19th century. The treaty of Nerchinsk established the border, and set up trade agreements--but the Russians became involved in the politics of Europe, and turned from an eastward view to a westward view. All the trade was local (i.e., from Siberia). Opium is not produced in Siberia.
As Coluber correctly points out, the opium in China came from the English. The Chinese demanded payment for any goods in silver. They barred the import of nearly everything the English had to offer. But the English hit upon the idea of importing opium from India, so that the trade route to China to get silk and tea was not a dead loss. Without the least regard for the consequences of the opium trade for the Chinese people, they persisted in bringing opium into the country illegally.
Here you will find Wikipedia's very brief but comprehensive description of the opium wars.