"It's been like therapy for me because I spend two hours in a booth by myself screaming and cussing," Cuoco said. "She's literally insane."
"The show's hilarious. I'm not trying to be biased -- the scripts and writing is genius," she added. "It's a lot of screaming and it's psychotic. I've never spoken like this before."
Cuoco said the show is fond of one curse word in particular.
"At one point we got some notes, it might have been from the network, it was like, 'It's just too many f-words.' We got this thing like, 'You've got to cut it back,'" she said. "It was like one after another."
Harley Quinn follows Harley Quinn and Poison Ivy (Lake Bell) after Harley Quinn leaves her boyfriend, the Joker (Alan Tudyk). DC Universe released a first trailer in July that shows Harley Quinn wreaking havoc.
Cuoco is known for playing Penny on the CBS sitcom The Big Bang Theory, which ended in May after a 12-season run. She will star in an HBO Max adaptation of the Chris Bohjalian novel The Flight Attendant.