caffeine vs caffein

caffeine and caffein both are nouns.

Word	Noun	Adjective	Verb	Adverb
caffeine	Yes	No	No	No
caffein	Yes	No	No	No

As nouns, caffeine and caffein are synonyms defined as:

caffeine and caffein: a bitter alkaloid found in coffee and tea that is responsible for their stimulating effects

caffeine (noun)	caffein (noun)
a bitter alkaloid found in coffee and tea that is responsible for their stimulating effects	a bitter alkaloid found in coffee and tea that is responsible for their stimulating effects