hypnogogic vs soporific

hypnogogic is not a noun while soporific is a noun.

Word	Noun	Adjective	Verb	Adverb
hypnogogic	No	Yes	No	No
soporific	Yes	Yes	No	No

As adjectives, hypnogogic and soporific are synonyms defined as:

Other synonyms of hypnogogic include hypnagogic, somniferous, somnific, soporiferous.

hypnogogic (noun)	soporific (noun)
	a drug that induces sleep

hypnogogic (adjective)	soporific (adjective)
sleep inducing	sleep inducing
	inducing mental lethargy