caffein vs caffeine

caffein and caffeine both are nouns.

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

As nouns, caffein and caffeine are synonyms defined as:

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

caffein (noun)	caffeine (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