Autopsy results found that Smith, 66, had high levels of the weight-loss drug phentermine in his system, coroner's spokesman Ed Winter said in a news release. He also had heart disease, an enlarged heart and up to 75 percent blockage of some blood vessels.
Smith's body was found on Aug. 3 by a caretaker at his home in Baldwin Hills.
The 6-foot-7 Smith was the top overall pick in the 1967 draft after playing at Michigan State, where he was an All-America pick in 1966. His No. 95 jersey was retired in 2006.
In his professional career, Smith spent five seasons with the Baltimore Colts, where he played on the 1971 Super Bowl team, and two seasons each with Oakland and Houston.
As an actor, he played soft-spoken Officer Moses Hightower in the "Police Academy" movie series. He made appearances on TV shows like "Good Times," "Charlie's Angels," and "Half Nelson," and was a regular in the ground-breaking Miller Lite commercials featuring retired players.
The Associated Press contributed to this report.