Maybe I have a liberal view of ballpark sizes but:

https://en.wikipedia.org/wiki/Ibogaine

"The action of ibogaine at the κ-opioid receptor may indeed contribute significantly to the psychoactive effects attributed to ibogaine ingestion; Salvia divinorum, another plant recognized for its strong hallucinogenic properties contains the chemical salvinorin A, which is a highly selective κ-opioid agonist"