if alcohol loosens your tongue, it makes you talk a lot without thinking carefully about what you are saying.
Her tongue loosened by drink, she began to say things that she would later regret.
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 (someone's) tongue
To cause (someone) to speak freely or carelessly or to divulge information.