The 22-year-old daughter of singers Whitney Houston and Bobby Brown was found face-down and unresponsive in a bathtub in her suburban Atlanta townhome Jan. 31, 2015, and died in hospice care July 26.
The medical examiner's office said it reviewed medical records, investigative files and other documents to determine how Brown likely died. Marijuana and alcohol were involved in the death, along with medications used for sedation or to treat anxiety, the medical examiner's office said.
"The underlying cause of death is the condition which starts the downhill course of events leading to death and in this case is the immersion associated with drug intoxication," the medical examiner's office said in the statement.
A judge on Thursday granted a request filed by media organizations to unseal the autopsy.
Brown's death was similar to the way her mother died.
Whitney Houston's body was found face-down in a foot of water in her bathtub at the Beverly Hilton Hotel just before the 2012 Grammy Awards. Authorities found prescription drugs in the suite and evidence of heart disease and cocaine in Houston's body but determined her death was an accidental drowning.
Bobbi Kristina Brown was found in the townhome she shared with Nick Gordon, an orphan three years older whom Houston had raised as her own. Brown referred to him as her husband.
Brown grew up in the shadow of her famous parents. She appeared with them in 2005 on the Bravo reality show "Being Bobby Brown" and attended award shows with her mother and father.
Houston and Bobby Brown were married 15 years before their relationship ended in 2007. Bobbi Kristina was their only child together.