In a letter to the campus community, Nikias wrote that Dr. Carmen Puliafito had been the subject of "various complaints" during nearly a decade as the dean of the Keck School of Medicine. Nikias said Puliafito received "disciplinary action and professional development coaching."
Nikias also provided new details about Puliafito's final months in the job before he resigned in the middle of the Spring 2016 term.
In 2015, USC Provost Michael Quick put Puliafito "on notice for being disengaged from his leadership duties," the president said.
"On March 11, 2016, two USC employees notified Provost Quick that Dr. Puliafito seemed further removed from his duties and expressed concerns about his behavior," Nikias wrote.
"The Provost consulted with me promptly and, as a result, confronted Dr. Puliafito. He chose to resign his position on March 24, 2016, and was placed on sabbatical leave."
Nikias stressed Friday that at the time of Puliafito's resignation "no university leader was aware of any illegal or illicit activities, which would have led to a review of his clinical responsibilities."
The president's letter was released hours after The Times provided USC with findings about Puliafito's behavior during his tenure heading the medical school.
It comes amid an outpouring of anger and questions about USC's handling of Puliafito, a Harvard-trained ophthalmologist.
The Times report last week described how Puliafito kept company with a circle of criminals and drug addicts and used methamphetamine and other drugs while serving as the dean. Photos and videos reviewed by The Times showed Puliafito, 66, and his friends, who were in their 20s and 30s, partying in 2015 and 2016.
The images include some in which Puliafito's companions are seen holding drug paraphernalia during an after-hours visit to the dean's office at USC's Health Sciences Campus in Boyle Heights.
One member of Puliafito's circle was a 21-year-old woman who overdosed in his presence at a Pasadena hotel three weeks before he abruptly quit as dean.
A witness to the incident told the newspaper of phoning Nikias' office, giving two employees an anonymous account of the overdose and demanding that USC take action against Puliafito.
Phone records reviewed by The Times showed the witness made a six-minute call to Nikias' office on March 14, 2016, 10 days after the overdose. The tipster said he did not expect a call back but had told the USC employees he would go to the media if action wasn't taken.
Last week, Puliafito's successor as dean, Dr. Rohit Varma, told a gathering of scores of students that USC had found "no evidence, particularly, of that phone call."
But Tuesday evening, a crisis management specialist representing USC, Charles Sipkins, said that Nikias' office did receive an anonymous call about Puliafito's presence at the hotel overdose. However, the anonymous report did not reach senior administrators, Sipkins said.
About three months after Puliafito stepped down, Nikias and other USC leaders hosted a catered reception for the former dean and praised his leadership of the medical school. Puliafito continued to accept new patients at campus clinics and represented the university at events, including a Keck-sponsored course at a Pasadena hotel earlier this month.
The Times made repeated inquiries over the last 15 months about Puliafito, in some cases describing information reporters had gathered about the dean and the overdose.
USC's leaders never responded to the inquiries. Numerous phone calls were not returned, emails went unanswered and a letter seeking an interview with Nikias to discuss Puliafito was returned to The Times by courier, unopened. The courier also delivered a letter of complaint from Brenda Maceo, USC's vice president for public relations and marketing, who said the reporter had "crossed the line" by visiting the Nikias home to deliver the letter.
On Friday, Nikias wrote that in the fall of 2016 "a communications staff member received an unsubstantiated tip about a Pasadena hotel incident."
He described a confrontation by administrators: "When we approached Dr. Puliafito about the incident, he stated a friend's daughter had overdosed at a Pasadena hotel and he had accompanied her to the hospital."
The president also said that last March, The Times did provide the university with "detailed questions about, and a copy of a 911 recording from the Pasadena hotel incident." The recording was "immediately referred to" a committee that assesses clinical competency, the Hospital Medical Staff, Nikias said.
"That body determined that there were no existing patient care complaints and no known clinical issues," the president said.
After The Times investigation was published on July 17, Nikias said the Hospital Medical Staff had reopened its investigation. The Medical Board of California also launched an investigation into Puliafito based on the newspaper's report, a spokeswoman confirmed.
Nikias said in his letter that after The Times published its story, the university learned "that two receptionists in the president's office received a call in March 2016 from a blocked number."
"The caller, who insisted on anonymity, raised concerns about an incident in a Pasadena hotel involving Dr. Puliafito. Neither receptionist found the claims or the caller credible, and so the information was not elevated and did not reach a senior administrator," Nikias wrote.
"Needless to say, we have already put into place a new system that documents and records all incoming calls to the president's office."
USC announced last week that it hired a former federal prosecutor who works for a law firm with close ties to the university to investigate the affair. Puliafito has been barred from the campus and from "any association with USC."
July 29, 7:45 a.m.: Updated with additional details about a phone call to USC from a witness to the hotel incident as well as passage from Friday's statement saying at the time of Puliafito's resignation USC officials were not aware of any drug use by former dean.