The news was shared by the Fulton County Medical Examiner's office in Atlanta on Friday (4 March), and a full autopsy report is expected to follow.
Marijuana, alcohol and medication for sedation and anxiety are the drugs involved, the office adds.
The conclusive post mortem took place in September 2015, and at the time, it was ruled that the results would not be made public.
A statement given read: “The Fulton County Medical Examiner has classified the cause and manner of Bobbi Kristina Brown's death based on information available as of September 25, 2015.
“However, a Fulton County Superior Court Order dated September 25, 2015 has been received Sealing the Autopsy Report and ordering the Medical Examiner to not release any further information to the public.
"The Fulton County District Attorney and Roswell Police Department have been informed of the Medical Examiner's findings."
Bobbi died on 26 July 2015, following a six month hospital stay, which began on 31 January, after she was found unresponsive in the bathtub at her Atlanta home.
Thousands of fans shared tributes online following Bobbi’s death, and Oprah Winfrey lead tributes from celebrities, with a simple Twitter post that read: “Peace at Last! #BobbiKristina.”
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