Lisa Marie Presley, the singer-songwriter and only child of Elvis Presley, died in January as a result of “a small bowel obstruction” caused by scar tissue that developed after bariatric surgery years ago, the Los Angeles County Medical Examiner’s office said on Thursday.

Ms. Presley had been complaining on Jan. 12 of severe abdominal pain, according to an autopsy report released on Thursday by the medical examiner’s office. Later that day, she was found unresponsive at her home in Calabasas, Calif., by her ex-husband, who was not named in the report.

Ms. Presley, 54, was taken by paramedics to a hospital, where she went into cardiac arrest and died that afternoon.

The report stated that although Ms. Presley had a previous history of drug use, she was sober “for the past few years.” Still, health problems appeared to have occurred after her bariatric surgery, which is generally considered a treatment option for people with a high body mass index who failed to lose weight with diet and exercise alone.

Juan M. Carrillo, a deputy medical examiner in Los Angeles County, described Ms. Presley’s health problems after the bariatric surgery as a “known long-term complication of this type of surgery.”

Ms. Presley was prescribed opiates after her surgery and after an infection, the report stated. She was then prescribed another type of medication so that she could be taken off the opiates.

The report noted that Ms. Presley had a “history of overmedicating; she was known to forget she had taken her medications and would take them again.”

The autopsy report said that toxicology results showed “therapeutic levels of oxycodone” in her blood. Buprenorphine, a medication to treat opioid addiction, was also present but did not contribute to her death, the report stated.

For months, she complained of abdominal pain, fevers, vomiting and nausea but did not seek medical attention, according to the report.

The Los Angeles County Coroner’s office had initially deferred ruling on Ms. Presley’s case. For months, officials said that a medical exam had been performed, but that a pathologist was awaiting further test results — including, potentially, a toxicology report — before releasing an official cause of death.

Two days before Ms. Presley’s death, she attended the Golden Globe Awards, at which “Elvis,” a biopic about her father’s life, was nominated for multiple awards. Some of her on-camera interviews on the red carpet prompted concern from fans and others who said she had appeared unsteady.

Ms. Presley was buried at Graceland, where a memorial was held in late January.

Weeks later, Priscilla Presley, Lisa Marie’s mother, who had long helped administer Elvis’s estate, went to court to challenge the validity of documents that say Lisa Marie’s daughter, the actress Riley Keough, is now the sole trustee.

The New York Times reported that although the Elvis brand today continues to take in more than $100 million a year as a licensing juggernaut, the family trust receives only a fraction of its proceeds.

In June, Ms. Keough agreed to provide Priscilla Presley, her grandmother and the former wife of Elvis Presley, with a lump-sum payment as part of a settlement that would resolve a dispute over control of the family trust, according to court documents.

Lawyers for the parties had sought to keep details of their agreement confidential, but the papers listed what appears to be a payment of $1 million.

On Wednesday, Ms. Keough was nominated for an Emmy for best actress in a limited series or TV movie for her titular role as the wild child in “Daisy Jones & the Six,” an Amazon mini-series about the rise and fall of a fictional 1970s band.