An opiate, such as heroin, morphine, or opium. It doesn't mean just any super-addictive drug, like meth. Just opioids like codeine.
Too often misused by propagandists and the ignorant as a word to describe any illegal drug that you're not supposed to use. This is probably because of its scary-sounding name, like some sort of hybridization between psychotic and nark, which just sounds awful.
Don't listen to anybody who uses it that way. They have no clue what they're talking about.
Wingnut health teacher: narcotics like marijuana and crack cocaine make your penis fall off. True story.
Me: pot is not a narcotic. You should now this. But you're paid by the government, so I guess I should be more realistic. God forbid you say something an educated doctor would say!!