loosen (one's) tongue
To cause one to speak uninhibitedly. Often refers to the effect of alcohol. A few drinks will loosen her tongue, and then I'm sure she'll tell me the secret without me even having to ask. I've never met a reporter like Courtney. She can loosen the tongue of even the cagiest politician.
loosen somebody’s ˈtongue
make somebody talk more freely than usual: A bottle of wine had loosened Harry’s tongue.