nicotinic acid vs niacin

nicotinic acid and niacin both are nouns.

Word	Noun	Adjective	Verb	Adverb
nicotinic acid	Yes	No	No	No
niacin	Yes	No	No	No

As nouns, nicotinic acid and niacin are synonyms defined as:

nicotinic acid and niacin: a B vitamin essential for the normal function of the nervous system and the gastrointestinal tract

nicotinic acid (noun)	niacin (noun)
a B vitamin essential for the normal function of the nervous system and the gastrointestinal tract	a B vitamin essential for the normal function of the nervous system and the gastrointestinal tract