AceShowbiz - Matthew Perry's ex-girlfriend has demanded further investigation after it was revealed that his death was caused by "acute effects of ketamine" and drowning. The 54-year-old actor - who was reportedly sober for 19 months before his death - had been undergoing ketamine infusion therapy for depression but his final session was over a week before he died, meaning the drug in his system was not from his treatment.

Kayti Edwards, Matthew's ex-girlfriend, has urged the authorities to take a closer look into the circumstances of his death. "I'm pretty sure that in Matthew's brain ketamine infusions at a doctor's would count as still being sober," she told The US Sun.

"In his brain it's not the same as going on the street to buy crack or heroin. That probably was the stepping stone for him to go back to doing drugs," Kayti added. "I wasn't surprised when the medical examiner's report dropped."

"I already knew what it was so it wasn't shocking to me. I wasn't there so I don't know exactly what happened but I do know Matthew as a person and a friend and I know the patterns that led up to this."

"I could see it from a mile away, he didn't seem right during the last couple weeks of his life. The sober people who knew him have never hung out with him when he was getting high so they wouldn't know the signs."

Matthew was found face-down and unresponsive in the hot tub of his Los Angeles home on October 28.