The girlfriend of former Anheuser-Busch CEO August Busch IV died at his home after accidentally overdosing on the painkiller oxycodone, the St. Louis County medical examiner said Wednesday.

Adrienne Martin, 27, of St. Charles, was found dead on the morning of Dec. 19 at Busch's sprawling estate in suburban St. Louis after spending the night at his home. He has said he woke up around 11 a.m. and tried to awaken Martin, but couldn't.

St. Louis County forensics administrator Suzanne McCune said the full report from Martin's toxicology exam wouldn't be released until the prosecuting attorney's investigation is complete. She would not say if any other drugs were found in Martin's system.

It wasn't immediately clear if the finding could result in any criminal charges. A spokesman for St. Louis County prosecutor Bob McCulloch said only that an investigation continues.

Busch's attorney, Art Margulis, said Bush was not aware that Martin had taken oxycodone. Margulis said he had not seen the medical examiner's report, and limited his comments to a brief statement.

"Last December, when this whole matter occurred, we released a statement saying that there were no suspicious circumstances, and nobody seemed to want to accept that. But I think the medical examiner report now makes it clear that the death was an accident," Margulis said.

Oxycodone is used to relieve moderate to severe pain, according to the National Institutes of Health. It is in a class of medications called opiate (narcotic) analgesics and works by changing the way the brain and nervous system respond to pain. It is commonly known by its brand name, OxyContin.

The Drug Enforcement Administration says abuse of Oxycodone has increased markedly in recent years.

Busch, 46, was the last in a long line of members of his family to head the iconic brewery, maker of Budweiser, Bud Light, Michelob, Busch and other beers. Despite his efforts to ward off a takeover, Anheuser-Busch Cos. Inc. was sold to Belgian brewer InBev in 2008, two years after Busch was named chief executive officer upon his father's retirement.

At Anheuser-Busch, Busch IV earned praise for his role in marketing and advertising that helped Anheuser-Busch control nearly 50 percent of the domestic beer market at the time of the merger. In life, he earned a reputation as a playboy and hard partier.

In 1983, Busch, then a University of Arizona student, left a bar near Tucson, Ariz., with a 22-year-old woman. His black Corvette crashed, and the woman was killed. Busch was found hours later at his home, and he suffered a fractured skull and claimed he had amnesia. After a seven-month investigation, authorities declined to press charges, citing a lack of evidence.

Two years later, Busch was acquitted by a jury in St. Louis on assault charges resulting from a police chase that ended with an officer shooting out a tire on his Mercedes-Benz.

Busch said his relationship with Martin was so strong he had put aside his playboy ways.

"She was the only girl I've ever been with that I didn't want to have someone on the side," Busch told the St. Louis Post-Dispatch in an interview last month. "You know, I'm this notorious bachelor who always wanted someone on the side, but I didn't with Adrienne."

Martin had done modeling work and was the mother of an 8-year-old son from a previous marriage. She was working as an assistant at a small alternative energy firm at the time of her death.

Friends had said she was strongly opposed to illegal drugs. But Busch had previously speculated that medication Martin was taking could have caused her death. He said she was taking Trazodone, a prescription medication to treat depression but also sometimes used to treat insomnia, according to the National Institutes of Health.

Also in the interview with the Post-Dispatch, Busch disputed a contention that there was a 42-minute gap between the time Martin was found unresponsive and a house employee, Michael Jung, called paramedics. Busch said Jung called immediately.

Busch and Martin had both been married before. Martin was married to a doctor, Kevin Martin, who now practices in Cape Girardeau, Mo. He is the father of her son. Busch married Kathryn Thatcher in 2006, but the marriage lasted less than three years. She told The Associated Press last month that the brewery was his life.

"He fought (the buyout) so hard, and he was so upset by it," Thatcher said. "He felt like he let everybody down."

Busch told the Post-Dispatch in the interview that he has struggled with depression since the takeover. But he called Martin's death "the saddest thing I've ever dealt with."

Busch is no longer involved in day-to-day operations at Anheuser-Busch but does sit on the InBev board of directors. He had largely disappeared from the public spotlight since the merger.