Presley Gerber Autopsy Complete After Death at Rehab Facility

Presley Gerber's autopsy has been completed after his suspected overdose ... TMZ has learned.

The Los Angeles County Medical Examiner performed the autopsy ... and Presley's official cause of death has been deferred.

We broke the story ... Presley died Sunday at a rehab facility at just 27 years old.

Sources familiar with the situation told us he had been living in a luxury rehab facility with several other people ... and the belief is he suffered an overdose. The 911 call came in as a suspected OD and police say no foul play is suspected.

Months before his death, Presley opened up about undergoing what he called an "Ibogaine Flood Dose" treatment ... saying he was "absolutely terrified" beforehand, but hoped the experience would help him find his way back to himself.

Ibogaine is a psychedelic drug that's been studied as a possible treatment for addiction. It's illegal in the United States, but is accessible in other countries ... including Mexico.

In his March post, Presley said letting go of control didn't come easy ... and he had finally faced what he'd been running from.

He ended the post on a hopeful note ... saying he was praying it would be the last time he'd have to return for treatment.

His family rallied around him in the comments ... with mom Cindy Crawford calling him a "warrior," dad Rande Gerber praising his courage, and sister Kaia Gerber saying she was "so damn proud."