B complex vs vitamin B

B complex and vitamin B both are nouns.

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

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

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

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

B complex (noun)	vitamin B (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