Opium
Like many people in the world of The Poppy War, Rin's foster parents sell opium to help them financially survive during difficult times. For many Chinese people in the world of The Poppy War, opium is a tool that allows them to survive, the consequences to those they sell the addictive drug be damned. Thematically, opium serves an important role: it sets the war mentioned at the center of the novel into motion and creates conflict, as both individuals and empires work hard to get (and sell) as much opium as possible. Opium is portrayed as a useful, but inherently harmful thing that has upended the world and destroyed the lives of countless people through the novel, including Rin.
Psychadelic drugs
Master Jiang (a professor in the world of The Poppy War) teaches Rin and the rest of the students at Sinegard, a prestigious Chinese military academy, about the power of psychedelic drugs (things like magic mushrooms and Ayahuasca). These powerful drugs allow the young students to look into the past and utilize god-like powers to bend the fabric of reality. Not only that, the drugs allow users to more powerfully meditate, allowing them to ruminate on their life and get in touch with a different, more calm version of themselves. The novel portrays these drugs positively and as tools; the novel shows that they can potentially give users a competitive advantage when studying and fighting wars.
