The 47-year-old was found dead in her car on July 29, with dozens of white pills scattered on the passenger seat. The San Diego Coroner's Office reports Barrymore died of acute intoxication, and had alcohol, methamphetamine, methadone, tramadol and nordiazepam in her system at the time of death.
Barrymore is half-sister to actress Drew Barrymore and daughter to John Barrymore and Nina Wayne.
"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 said in a statement shortly after Jessica's death.
Barrymore died two days before her 48th birthday.