vitamin G vs vitamin B complex

vitamin G and vitamin B complex both are nouns.

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

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

vitamin G: a B vitamin that prevents skin lesions and weight loss
vitamin B complex: originally thought to be a single vitamin but now separated into several B vitamins

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

vitamin G (noun)	vitamin B complex (noun)
a B vitamin that prevents skin lesions and weight loss	originally thought to be a single vitamin but now separated into several B vitamins