The news station says an energy drink and dozens of white pills were found in the vehicle. An autopsy has been scheduled.
Drew told People in a statement, "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.”
Jessica, who would have turned 48 on July 31, is the daughter John Drew Barrymore and his third wife, Nina Wayne. John died of cancer in 2003.
Jessica attended San Diego School of Creative and Performing Arts and lived in San Marcos.