The San Diego County Medical Examiner's Office indicated in an autopsy report that a toxicology screening revealed only traces of commonly prescribed medications for sleeping disorders and arthritic pain, U-T San Diego reported.
"No alcohol, common drugs of abuse or other medications (base and acid/neutral screens) were detected," the report said.
"Based on the autopsy finding and the circumstances surrounding the death, as currently understood, the cause of death is perforating gunshot wound of chest, and the manner of death is suicide," Deputy Medical Examiner Craig Nelson said in the report.
Seau, 43, played 17 years in the NFL and made the Pro Bowl a dozen times. He was drafted by the Chargers in 1990 out of the University of Southern California and played in San Diego through 2003.
Some have speculated repeated blows to his head during his 20-year NFL career could have been a contributing factor, and his brain tissue was sent to the National Institutes of Health at the request of relatives, Nelson said.