A type of birth control in which one partner drugs the other with a sleeping pill prior to sex, with the intended effect that such person will fall asleep prior to ejaculation. This method is even less effective than the rhythm method and is not recommended.
"We're out of condoms, but it's no problem... I've got enough ambien for us to use the circadian rhythm method."
"Well, she's not on THE pill, but she's on A pill... circadian rhythm method style."