Amanda Bynes -- The Cocktail Is Working!!!

Amanda Bynes is doing remarkably better ... she's stabilized, not hearing voices and it's all because of a cocktail ... TMZ has learned.

Sources familiar with the situation tell TMZ ... doctors at the psychiatric hospital where she's being held have given her a combination of meds -- referred to as a cocktail -- to control what appears to be schizophrenia.

Our sources say Amanda responded quickly and dramatically. We're told in the last 3 days, Amanda has stopped talking to herself and stopped insulting people. To the contrary, we're told she's become downright polite, even saying "please" and "thank you." She has shown no signs of violence.

The progress is all the more stunning because these cocktails are notoriously difficult to gauge -- getting the right combination of meds with the right doses is something of a crap shoot. Our sources say the meds take 7 to 10 days to fully kick in, so they're not declaring victory yet, but they're optimistic.

But there's an ironic twist. Amanda is scheduled to have a court hearing today ... where she's trying to get out of the psych hospital. The fact that she's doing better can actually help her case, but we're told doctors are confident the judge will not let her out for several reasons. First, it's unclear if the meds will work long-term. Also, it's highly uncertain she'll voluntarily take the drugs.

One more thing. There are reports Amanda's parents may back off the conservatorship if she does better in the psych ward. Our sources say that is "absolutely untrue." Amanda's parents feel it's essential for her to get long-term care and supervision.