Drew Barrymore's half-sister died of an accidental overdose.

The San Diego Coroner's Office in California has confirmed Jessica Barrymore died from acute intoxication and had both alcohol and drugs in her system at the time of her death on July 29.

According to PEOPLE.com, among the substances discovered by the coroner include methamphetamine, methadone, tramadol and nordiazepam.

The 47 year old was found unresponsive in a parked car that blocked her driveway by a local fire department.

Jessica - who shared a father with the A-list actress - died just days before what would have been her 48th birthday

Speaking at the time of her half-sibling's death, Drew, 39, said: ''Although I only met her briefly, I wish her and her loved ones as much peace as possible, and I'm so incredibly sorry for their loss.''

Drew and Jessica's half-brother John Barrymore previously admitted he wasn't convinced she had committed suicide and correctly predicted her death was an accident.

He said: ''It looks like it was a drug misadventure. Mixing alcohol and pills. I seriously doubt she took her own life.

''There were some empty vodka bottles, a couple bags of meth and a variety of pills in the car. My guess is that it was the booze and pills, like with Heath Ledger.

''She visited her mum the day before, and her mum is almost gone. It was hard for her to see her. I doubt she tried to kill herself, though ... I predict it will be that - mixing booze and pills and taking too many.''