The autopsy on Adams, 26, was performed in Anderson, S.C. The toxicology test will be performed by South Carolina's law enforcement division and results are expected to be returned in the next two to three months.
"We are stunned and saddened by the news of Gaines' passing," the team said in a statement Sunday. "Our prayers are with his family during this difficult time."
Adams was selected fourth overall in the 2007 NFL draft by Tampa Bay, but was traded to the Chicago Bears in October 2009. He had not been able to live up to expectations that he would revive the Buccaneers' once-feared pass rush, having just 17 tackles and one sack in 15 games this season.
The 6-foot-5, 258-pound defensive end was well-known among Clemson fans for breaking up Wake Forest's field goal try and returning it for a touchdown in 2006 to defeat the Demon Deacons.