The classic emergency in opioid overdose is failing respiration with pinpoint pupils and depressed consciousness. The drug that reverses this is naloxone.
Mechanism:
$\text{Naloxone} \dashv \mu\text{-opioid receptor (competitive antagonist)}$
By displacing the opioid agonist from $\mu$ receptors, naloxone restores the respiratory drive within minutes when given intravenously, intramuscularly or intranasally. A key caution is its short half-life relative to many opioids, so the patient can re-sedate (“renarcotisation”) and may need repeat boluses or a continuous infusion, especially with methadone or extended-release formulations.
Antidote pairings to keep straight:
$\text{Benzodiazepines} \rightarrow \text{Flumazenil}$
$\text{Organophosphates} \rightarrow \text{Atropine (+ pralidoxime)}$
$\text{Paracetamol} \rightarrow \text{N-acetylcysteine}$
Only naloxone targets the opioid receptor, so it is the correct choice for opioid poisoning.
\[\boxed{\text{Opioid antidote} = \text{Naloxone}}\]