The Oklahoma medical examiner ruled the crash that killed shale pioneer Aubrey McClendon was an accident, according to the autopsy report released Wednesday.

No alcohol was involved in the accident, but an unspecified amount of one drug—doxylamine, which can be found over the counter and used as an antihistamine or to treat insomnia—was found in Mr. McClendon’s system, the report said.

Mr. McClendon suffered a number of injuries in the single-vehicle crash, including several broken ribs, a broken pelvis and a broken back, as well as lacerations to several internal organs, according to the autopsy report.

Those findings are consistent with the medical examiner’s previous determination that the former chief executive of Chesapeake Energy Corp. died of multiple blunt force trauma.

The report shows that while Mr. McClendon’s heart was damaged by the crash, he didn’t appear to suffer a heart-related medical event.