Which substance enhances the effects of GABA in the central nervous system?

Benzodiazepines are a class of medications that enhance the effects of gamma-aminobutyric acid (GABA), which is the primary inhibitory neurotransmitter in the central nervous system. By increasing the activity of GABA at the GABA-A receptor, benzodiazepines promote relaxation, reduce anxiety, and create a calming effect. This mechanism makes them effective for treating conditions such as anxiety disorders, insomnia, and certain seizure disorders.

The other substances listed do not primarily function through GABA enhancement. Antidepressants mainly target neurotransmitters like serotonin and norepinephrine to treat depression and anxiety, while stimulants typically increase levels of norepinephrine and dopamine to elevate mood and energy levels. Narcotics, or opioids, primarily act on the opioid receptors in the brain to provide pain relief and can produce euphoria but do not enhance GABA activity specifically. Therefore, the distinct action of benzodiazepines on the GABA system makes them the correct choice for this question.