The ENQUIRER exclusively reports O.J. Simpson's violent drug withdrawal behind bars.

Life behind bars is unbearable for the non-juiced Juice. Simpson's in constant agony because he can no longer take large amounts of painkilling medications.

For years he's enjoyed massive doses of painkillers because of alleged severe arthritis.

But jail docs have drastically reduced his daily dose as he withdraws from the drugs. 

His anguished pleas to jailers for more painkillers go ignored, say sources.

"Sometimes he screams at his jailers, demanding pills, but his cries are going ignored until his evaluation is complete," a source divulged. 

O.J. has been overmedicating for years and now he's paying the price.

And to make his life even more miserable, his kids are bitter and angry, confide insiders.

His son Justin, 20, is livid at O.J.'s botched burglary attempt and estranged daughter Arnelle isn't "shedding any tears," according to an insider.

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