The woman was identified as Adrienne N. Martin, of St. Charles, Missouri.
Police were called Sunday afternoon to the St. Louis suburb of Huntleigh and found her body in Busch's gated home. St. Louis County forensic administrator Suzanne McCune said Thursday there were no signs of illness or trauma. An autopsy was conducted but toxicology results could take four to six weeks.
A statement from Frontenac police (whose area of coverage includes Huntleigh) said the department received an emergency call Sunday afternoon about an "unresponsive person" at the home. Martin was deceased when paramedics and officers arrived, the release said.
The news release did not say if the death was considered suspicious, or why news of the death was not announced until four days later.
Art Margulis, an attorney for Busch, said Martin was a friend of Busch who was visiting the home and there was "absolutely nothing suspicious" about her death.
"It was a tragic death of a young woman," he said. Margulis told the St. Louis Post-Dispatch that Martin and Busch had been dating for at least a year.
Margulis did not confirm or deny whether Busch was at home at the time of Martin's death, reports CBS Affiliate KMOV correspondent Matt Sczesny.
McCune declined to speculate on the investigation or the cause of death. The St. Louis Post-Dispatch quoted an unnamed law enforcement source as saying the case was being investigated as a possible overdose. McCune would only say that an overdose was among the possible causes.
Citing a divorce file, the Post-Dispatch reported that Martin was married in 2002 to a 45-year-old man but they separated in February 2009. The couple had joint custody of an 8-year-old son, the paper reported.
A woman identified as Adrienne Nicole Martin, from the St. Louis area and the same age as the victim, posted on the website iStudio.com that she was studying to be an art therapist and was hoping to become a model. "I really would like to do beer advertising," the woman wrote in the posting.
Busch, 46, was chief executive at Anheuser-Busch from 2006 until the maker of Budweiser, Bud Light and other beers was purchased by InBev in 2008. The $52 billion merger created the world's largest brewery. Busch remains a member of the board of directors for InBev.
The Post-Dispatch reported that Busch and his wife of 2½ years divorced in 2009.
In 1983, Busch, then a 20-year-old University of Arizona student, left a bar with a 22-year-old woman. His black Corvette crashed and the woman, Michele Frederick, was killed. Busch was found hours later at his home. He suffered a fractured skull and claimed he had amnesia. After a seven-month investigation, authorities declined to press criminal charges, citing a lack of evidence.