As nouns the difference between drowsiness and stupefacient
is that drowsiness is state of being drowsy while stupefacient is (medical) a drug that has the above effect.
As an adjective stupefacient is
(medical) inducing stupor or drowsiness (with a drug such as a narcotic or an anaesthetic).
stupefacient
English
Adjective
(
en adjective)
(medical) inducing stupor or drowsiness (with a drug such as a narcotic or an anaesthetic)
Noun
(
en noun)
(medical) a drug that has the above effect
----