Diddy's Party Life Is Over, Prison Time Likely a Blessing, Dr. Drew Says

Prior to his prison sentence, Diddy claimed to be a changed man ... but the true test won't occur until he is out ... 'cause he must say RIP to his party life, Dr. Drew tells TMZ.

As you know ... Diddy got four years behind bars for his transportation for prostitution convictions -- and while pleading his case for his immediate freedom, the mogul swore he was a new man.

Dr. Drew tells TMZ … he truly believes Diddy meant what he said -- he is a changed man who's learned some hard lessons -- but he's facing a major uphill battle if he wants the change to be permanent.

In Drew's determination, Diddy is clearly a sex addict ... and he's going to require years of extensive treatment after he's outta the joint ... or it's likely he'll plummet right back to rock bottom.

The good doctor tells us ... Diddy’s life has got be vastly different once he’s a free man again … 'cause forced sobriety ain't going to hold. So, in other words -- the parties and freak-offs better be over.

As far as a silver lining, Dr. Drew says being cut off from the overindulgence of sex and alleged drug abuse is a possible blessing. If Diddy is serious about changing his life … being locked away for a few years will allow him to build a better sobriety foundation to build real self-work on once he's free.