Soporidine is a powerful sedative secreted from Bucollosiscia, a hybridized bacterium. The bacteria themselves are harmless, but the soporidine they secrete can be lethal. When applied, the affected individual has no thoughts nor dreams. Although difficult, it is able to be produced—sleep-inducing flowers burned with Everblaze can sustain the bacteria long enough to harvest the sedative. The Neverseen produced many batches of soporidine in order to threaten both Elves and humans, as they are the only ones with the cure.
Soporodine is described as soft and gloopy—like paint. It is typically vivid purple when it comes into contact with skin, however, the type developed by Lady Gisela (used to sedate Silveny and Greyfell) is deep blue due to chemical changes for its effects on alicorn physiology. The antidote for the purple type is green, and the antidote for the blue variety is orange.
In order for Alvar to complete his mission without revealing the Neverseen's secrets, the Neverseen sedated Alvar with soporidine and left him in Nightfall. He was awoken at the end of book six, with the book ending with Sophie discovering that he had lost his memories.