somniferous vs soporific

somniferous is not a noun while soporific is a noun.

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

As adjectives, somniferous and soporific are synonyms defined as:

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

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

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