Jessica Barrymore, and Drew Barrymore (inset)
Jessica Barrymore/Facebook; Inset: Sara De Boer/Startraks
08/27/2014 AT 02:35 PM EDT
Last month's death of Jessica Barrymore, half sister to Drew Barrymore
, was caused by an accidental overdose, according to the San Diego Coroner's Office.
Jessica's body was discovered
in National City, California, on July 29, when a woman found Jessica in a parked car that was blocking her driveway. The Fire Department responded and confirmed her death without medical intervention, according to the coroner.
Results of the coroner's investigation show that Jessica died of acute intoxication and had a combination of alcohol and drugs – including methamphetamine, methadone, tramadol and nordiazepam – in her system upon her death, which took place two days before what would have been her 48th birthday.
"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 previously said in a statement released to PEOPLE.