In her posthumous memoir From Here to the Great Unknown, Lisa Marie Presley opens up even deeper about her opioid addiction.

Lisa Marie — who died at age 54 in January 2023 of a small bowel obstruction, a long-term complication from bariatric surgery — had long been candid about how she became addicted to prescription painkillers following the 2008 birth of her twins Finley and Harper (with ex Michael Lockwood, her husband from 2006 to 2021).

But now, for the first time, she’s unveiling just how intense her addiction got.

“It escalated to 80 pills a day,” Lisa Marie writes. “It took more and more to get high, and I honestly don’t know when your body decides it can’t deal with it anymore. But it does decide at some point.”

Lisa Marie writes that for a couple of years her drug use was “recreational,” but then “it wasn’t.”

“It was an absolute matter of addiction, withdrawal in the big leagues,” she writes. “I just wanted to check out. It was too painful to be sober.”

In the book, Lisa Marie’s daughter, Riley Keough, 35, writes that her mom started taking opioids for the pain of her delivery by c-section, and “then she progressed to taking them to sleep.” She says her mom felt “shame” about becoming an addict with two young children.

Riley writes the family was surprised by Lisa Marie’s addiction, as her mom wouldn’t even take Advil or Tylenol as an adult. Despite a stint with drugs as a teenager, Lisa Marie had never touched them again until that point.

After being hospitalized for her addiction, Lisa Marie was sent to court-ordered rehab in L.A. There, Riley writes her mom decided to have bariatric surgery.

“I didn’t feel she was ready to be sober,” Riley writes.

Following rehab, Riley writes Lisa Marie wasn’t taking narcotics anymore but was getting high “on the post-rehab cocktail.” She finally decided to get sober when she was hospitalized again, this time for a seizure.

“She had been very chastened by the seizure,” Riley writes.

To finish From Here to the Great Unknown, Riley listened to taped memories her mom had recorded. Riley told PEOPLE in an exclusive email interview for last week’s cover story that her “mom’s descent into addiction” was an “incredibly difficult” chapter to write, as were the chapters about her death and the 2020 suicide death of her brother Benjamin after his own struggle with addiction.

Riley hopes the book sheds new light on who her mother was.

“I hope that in an extraordinary circumstance, people relate to a very human experience of love, heartbreak, loss, addiction and family,” she said. “[My mom] wanted to write a book in the hopes that someone could read her story and relate to her, to know that they’re not alone in the world. Her hope with this book was just human connection. So that’s mine.”

From Here to the Great Unknown is available now.