St. Louis County Medical Examiner Mary Case confirmed to the Washington Post that Brown, 18, had been shot in the head and chest multiple times.
Case refused to elaborate further, but a person familiar with the investigation said Brown had been shot six to eight times, from the front, which corroborates the family's autopsy.
The source added that Brown had marijuana in his system when he was shot and killed by Ferguson Police Officer Darren Wilson on August 9.
Supporters of Brown have been bracing themselves for such results, fearing they could be used to vilify Brown and shift the blame to him for his death.
According to NORML, a nonprofit dedicated to reforming marijuana law, the presence of THC, the active chemical in marijuana, can be detected for up to seven days in a blood test.
The St. Louis County Medical Examiner's report was filed with the county prosecutor's office Friday, but has not been made public.
A third autopsy, to be conducted by the Department of Justice, has been ordered by Attorney General Eric Holder. Retired New York City Chief Medical Examiner Michael Baden, who conducted the family's autopsy, did not have access to toxicology reports or Brown's clothing.