Squalenol-5
Squalenol-5 is derived from oil pressed from genetically-modified olives that were also grown in a strong thaumaturgical field. It’s a remarkably effective antidominant; even a trace presence in the bloodstream can prevent a demon from taking full possession of a victim, as well as significantly boost the victim’s own willpower when it comes to expelling the demon naturally. Squalenol-5 is also nontoxic (well, unless you’re a demon) and tastes more or less like it was derived from olive oil. Put it in a salad dressing and nobody would notice.