A rep for Whitney Houston says the singer is receiving treatment in an out-patient rehab program for drugs and alcohol as part of a "long-standing " recovery process.
TMZ broke the story ... Houston voluntarily enrolled in the program around 10 days ago.
Houston has admitted her problems with substance abuse in the past ... but TMZ has learned the demons have resurfaced.
A music industry source who was with Whitney two weeks ago tells us, "She was plastered and she was a mess."
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