TMZ Sports reports the 37-year-old "had ingested fentanyl and other dangerous substances prior to his death" in May 2021.
Following an autopsy and too screen, health officials ruled Brennan's death as accidental, caused by a lethal combination of fentanyl, while methamphetamine, amphetamine and ethanol were also found in his system.
The former University of Hawaii standout was undergoing treatment at a drug rehab facility in Southern California at the time of the accidental overdose, which led to him being rushed to the hospital, where he was later pronounced dead.
Brennan transferred to Hawaii from Saddleback College (Mission Viejo, Cali.) after being dismissed from the University of Colorado. The California native led the Rainbow Warriors to a WAC championship and Sugar Bowl appearance, while also becoming Hawaii's first Heisman Trophy finalist in program history, during the 2007 college football season.
Brennan, a two-time first-team All-WAC quarterback and WAC Offensive Player of the Year, was also a finalist for the Johnny Unitas Award, presented to the NCAA's top senior quarterback, a semifinalist for the Davey O'Brien Award, and was listed on the preseason watch list for numerous other national accolades entering his final season at Hawaii.
Brennan finished his collegiate career as the NCAA's all-time leader in touchdown passes (131) and held the NCAA single-season touchdown passing record (58) from 2007-2019 until it was broken by then-LSU quarterback and eventual Heisman Trophy winner Joe Burrow (59.)
Brennan was selected by the Washington Football Team in the sixth-round of the 2008 NFL Draft and played two seasons with the franchise before being traded to the Baltimore Ravens in August 2010. The Ravens released Brennan days later and he signed with the then-Oakland [now Las Vegas] Raiders' practice squad for one month before making appearances in the United Football League, Canadian Football League and Arena Football League prior to his retirement.