Drug intoxication and having her face immersed in water led to the death of Bobbi Kristina Brown last year, according to a coroner.

Fulton County Medical Examiner's office in Atlanta released a statement on the death of the 22-year-old daughter of singers Whitney Houston and Bobby Brown as officials prepare to release the full post-mortem report.

Brown was found face-down and unresponsive in a bath in her suburban Atlanta home on January 31 last year, and died in hospice care on July 26.

The office said it reviewed medical records, investigative files and other documents to determine how Brown died. Marijuana and alcohol were involved, along with medication used for sedation or to treat anxiety.

A judge on Thursday granted a request filed by media organisations to unseal the post-mortem report.

The statement from 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."

Brown's death was similar to the way her mother died.

Houston's body was found face-down in a foot of water in her bath 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 her body but determined her death was an accidental drowning.

Brown was found in the home she shared with Nick Gordon, an orphan three years older whom Houston had raised as her own. Brown referred to him as her husband.

She grew up in the shadow of her famous parents. She appeared with them in 2005 on the TV reality show Being Bobby Brown and attended award shows with them.

Houston and Bobby Brown were married for 15 years before their relationship ended in 2007. Bobbi Kristina was their only child together