Which of the following describes a narcotic?

A narcotic is primarily defined as a substance that can relieve pain while having the potential for causing dependency, making option B the correct description. Narcotics, often categorized under opioids, work by binding to specific receptors in the brain and spinal cord, which helps to decrease the perception of pain. However, their misuse can lead to physical or psychological dependence due to their action on the brain's reward systems.

The other options do not accurately reflect the definition of a narcotic. While a substance that promotes sleep might suggest the sedative effects of some narcotics, it does not capture the pain relief and potential for dependency that characterizes narcotics. A stimulant, as mentioned in another option, is conversely designed to increase energy and alertness, which is contrary to the sedative nature of narcotics. Lastly, a herbal remedy may be used for pain relief but does not qualify as a narcotic since it does not possess the properties associated with medicinal narcotics or opioids.