Which of the following is a narcotic antagonist?

Naloxone is a narcotic antagonist that is primarily used for the treatment of opioid overdoses. It works by competitively binding to opioid receptors in the brain, effectively reversing the effects of narcotics. This action can counteract the respiratory depression and sedation caused by opioids, making it a critical medication in emergency situations where opioid overdose is suspected.

When considering the other options, they are not classified as narcotic antagonists. Flumazenil is a benzodiazepine antagonist, used to reverse the effects of benzodiazepines, not narcotics. Ketamine is a dissociative anesthetic, mainly affecting NMDA receptors, and it does not have narcotic antagonist properties. Codeine is an opioid itself and functions as a narcotic rather than an antagonist. Therefore, the only option that correctly identifies a narcotic antagonist is naloxone.