The general term is antidote. Another term is antitoxin and in the case of venom poisonings (e.g. snake, spider, scorpion) antivenin.
If by decoding, you mean the etymology of the word...it is derived from the latin word antidotum, meaning "a remedy against poison"
toxemia
Toxicogenesis? or Pathogenesis?
The medical term for poison produced by an organism is "toxin."
detoxification defined as removal of poison from a tissue or substance
Antisepsis
against, doesnt have to be medical, antibacterial= against bacteria, antichrist= against christ, just a latin prefix meaning against
The medical prefix "contra-" means against or opposite.
Frottage
antidepressant
Viral means pertaining to a virus. Virus is a latin word that means poison. The study of virus is called virology.
"Contraception" literally translates as against conception or opposite conception.