Uma Thurman CRACKING Under Bitter Custody Battle!

Pill-popping Uma Thurman may be headed for a dramatic breakdown amid a bruising custody battle with her ex-fiancé, sources told RadarOnline.com.

As an insider exclusively revealed, "The stress has got to be OVERWHELMING for Uma to have her darkest secrets revealed and name dragged through the mud!"

"She's already very stressed out, as was pointed out during the trial."

It was during the Manhattan court smack-down that Uma's ex Arpad "Arki" Busson, 54, accused the Kill Bill starlet of having a "serious mental illness" and chasing a cocktail of "serious psychiatric drugs" with booze.

"Ms. Thurman, is it your usual practice to consume alcoholic beverages in the evening?" asked Arpad's lawyer.

"Objection!" Uma's attorney yelled. "This is completely improper."

RadarOnline.com can now reveal Uma, 46, is taking a powerful cocktail of Triazolam, Wellbutrin and Klonopin for depression, anxiety and insomnia, according to court transcripts.

What's more, a court-appointed psychologist testified Uma suffers from "some attention-deficit/hyperactivity disorder" and a "mild learning disability," but no "personality disorder."

Uma is battling the on-again-off-again French financier over his demand for more visitation hours with their 4-year-old daughter, Luna.

She began dating Arpad in 2007 — but the couple called it quits in April 2014.

The court psychologist said on the stand that "stress is not easy for" Uma — even without the horror of a custody fight!

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