A statement from the Orange County coroner's office says Dorman was under the care of a physician when the 70-year-old was found dead in his car Friday at his home in the coastal town of Laguna Niguel.
Authorities have said Dorman may have been on his way to a doctor's appointment when he died.
No services have been announced.
Iron Butterfly rose to prominence in the late 1960s. According to the band's website, its second album, "In-A-Gadda-Da-Vida," sold more than 30 million copies. The title track's distinctive notes have been featured in numerous films and TV shows.