cobalamin vs vitamin B complex

cobalamin and vitamin B complex both are nouns.

Word	Noun	Adjective	Verb	Adverb
cobalamin	Yes	No	No	No
vitamin B complex	Yes	No	No	No

As nouns, vitamin B complex is a hypernym of cobalamin; that is, vitamin B complex is a word with a broader meaning than cobalamin:

cobalamin: a B vitamin that is used to treat pernicious anemia
vitamin B complex: originally thought to be a single vitamin but now separated into several B vitamins

Other hypernyms of cobalamin include B-complex vitamin, B, B complex, B vitamin, vitamin B.

cobalamin (noun)	vitamin B complex (noun)
a B vitamin that is used to treat pernicious anemia	originally thought to be a single vitamin but now separated into several B vitamins