regardless vs disregarding

regardless is an adjective but disregarding is not an adjective.

Word	Noun	Adjective	Verb	Adverb
regardless	No	Yes	No	Yes
disregarding	No	No	No	Yes

As adverbs, regardless and disregarding are synonyms defined as:

regardless and disregarding: in spite of everything; without regard to drawbacks

Other synonyms of regardless include disregardless, irrespective, no matter.

regardless (adjective)	disregarding (adjective)
(usually followed by `of') without due thought or consideration

regardless (adverb)	disregarding (adverb)
in spite of everything; without regard to drawbacks	in spite of everything; without regard to drawbacks