I'm sorry, I've never seen any mention linking racism to be caused by the Chinese opium epidemic. Because it's not true. Racism is the belief that one's own race is superior to others. In order for the opium epidemic to have caused it initially, the common person would have had to know about it at some point.

Due to the speed at which information traveled, hardly anyone was aware, let alone understood, that there was an entire country being controlled by opium sales from Britain.

What I'm trying to point out is that a racist individual will be racist no matter the cause, they were predisposed to think their race superior.