like mad vs like crazy

like mad and like crazy both are adverbs.

Word	Noun	Adjective	Verb	Adverb
like mad	No	No	No	Yes
like crazy	No	No	No	Yes

As adverbs, like mad and like crazy are synonyms defined as:

like mad and like crazy: (informal) with great speed or effort or intensity; used for emphasis

Other synonyms of like mad include like hell, like sin, like the devil, like thunder.

like mad (adverb)	like crazy (adverb)
(informal) with great speed or effort or intensity; used for emphasis	(informal) with great speed or effort or intensity; used for emphasis