Closet Drinker

A person who tries to keep his/her excess alcohol use or frank alcoholism a secret from friends and/or family, by using mouthwash, drinking alone, etc.
References in periodicals archive ?
When you become addicted, you become very much aware that you shouldn't show that in public places, so you become more and more of a closet drinker," he explains.
He's a closet drinker, is scared of entering lifts, has wild mood swings -- in short, a loner with too many problems.