Antidote
An agent that counteracts a poison and neutralizes its effects.
A chemical antidote is a substance that unites with a poison to form a harmless chemical compound.
A mechanical antidote is a substance that prevents the absorption of a poison from the intestine into the body.
The word 'antidote' is from the Greek antidotos which came from anti, against, + dotos, what is given = what is given against (something).