Narcotics act on the central nervous system by producing a what effect

Narcotics act on the Central Nervous System (CNS) by producing soothing, lulling, dulling and pleasant effects.
The effect, of course, depends on the drug, but it has been shown that one common thread is that drugs of abuse alter the brain’s reward pathway in different ways. Drugs are involved in a communication system in the brain and interfering with the way neurons normally send, receive, and process information.  Some of those narcotics can cause the neurons to release abnormally large amounts of neurotransmitters or prevent the normal recycling of these brain chemicals. For example, marijuana and its active substance THC stimulates dopamine release, making the whole experience quite pleasant. Other drugs, like heroin, are painkillers because they act on opioid receptors in the brain and spinal cord.