B complex vs B vitamin

B complex and B vitamin both are nouns.

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

As nouns, B complex and B vitamin are synonyms defined as:

B complex and B vitamin: originally thought to be a single vitamin but now separated into several B vitamins

Other synonyms of B complex include B-complex vitamin, B, vitamin B, vitamin B complex.

B complex (noun)	B vitamin (noun)
originally thought to be a single vitamin but now separated into several B vitamins	originally thought to be a single vitamin but now separated into several B vitamins