brain / head / chief, principal

direct

directness

action, operation / effect / function

act on

A substance with mystical properties, especially one that has an effect on the body, health, or lifespan.

(anatomy) the brain / (by extension, figuratively) one's brains, one's mental functioning

(archaic, anatomy) the brain / (archaic, by extension) the head

brain; brains / mind; intellect; understanding

A medicine or drug.