Lisa Marie Presley was on an extreme weight loss regimen in the months leading up to her death, because she wanted to look her best to celebrate the “Elvis” movie during the various awards ceremonies … family sources tell TMZ.

Our sources say … 2 months before the Golden Globes, Lisa Marie got plastic surgery and began taking weight loss meds. We’re told she lost 40 to 50 pounds in the 6 weeks leading up to the Globes.

What’s more … our family sources say Lisa Marie was taking opioids again — an addiction she struggled with for years.

Lisa did 2 interviews during the Globes that caused alarm … she was gaunt, slurring her words and so unsteady she had to hold on to a friend as she spoke. Dr. Drew tells TMZ it was obvious just watching the video … there were clear markers Lisa was on something.

Family and law enforcement sources tell TMZ … on the morning she died, Lisa complained of abdominal pain.

Lisa’s cause of death has been deferred pending toxicology results, which could take several months.

As the cause of death remains undetermined, there’s already a family war brewing. Priscilla Presley, Lisa Marie’s mom, has filed legal docs challenging a change her daughter allegedly made to her trust. Lisa had appointed Priscilla trustee in 2010, but cut her out in a 2016 amendment replacing her with her daughter, Riley Keough. Priscilla is suggesting in the docs that the 2016 amendment is fraudulent.

TMZ has prepared a documentary on new details of Lisa’s death, a possible custody fight and a battle over money.  The doc, “TMZ Investigates: Lisa Marie Presley: Unending Tragedy,” airs on FOX tonight, January 30th, at 8 PM.