It’s not, the BtmG literally means narcotics drugs act.
https://www.bfarm.de/EN/Federal-Opium-Agency/Narcotic-drugs/...
https://en.wikipedia.org/wiki/Narcotic_Drugs_Act
Interestingly, in both cases the semantic shift seems to have been caused by the enactment of laws to control drugs. The legal term these days is probably "controlled substance" in English, but "narcotic" now definitely refers to many drugs that are not medically narcotic.