The medical examiner said Tuesday that Colin Kroll died of the combined effects of fentanyl, heroin and cocaine.
Police found Kroll at his apartment in December after getting a request for a wellness check.
Kroll was the chief executive of the trivia app, which live-streams short trivia shows to users and became popular after its release in 2017.
He also was a founder of Vine, an app built around six-second videos, and worked for a period at Twitter.
VIDEO: What is HQ Trivia?