Final answer:
An antidote is a substance that counteracts the effects of a poison. Antidotes work by neutralizing the toxin, promoting its metabolism, or reversing its toxic effects.
Step-by-step explanation:
A drug or other substance that counters the action of a poison is called an antidote. Antidotes can vary widely in their chemical nature and mode of action. Some may directly neutralize the toxic effects of a poison, while others may work by initiating a chemical reaction that renders the poison harmless, or by enhancing the body's natural metabolism to detoxify the poison. For example, the antidote for atropine poisoning is a muscarinic agonist, which counteracts the effect of atropine on the nervous system.