The 38-year-old star of 80s films such as The Lost Boys was found dead last week after an apparent overdose in the apartment he shared with his mother.

Investigators found no illegal drugs but did discover four prescriptions in Haim's name.

The bottles reportedly contained Vicodin, Valium, haloperidol and a muscle relaxant.

They were found as part of an investigation launched to crack down on the increasing number of prescriptions obtained with notes from stolen or fake doctors' pads, California Attorney General Jerry Brown said.

"Corey Haim's death is yet another tragedy linked to the growing problem of prescription-drug abuse," said Mr Brown, who recently took part in the investigation into Michael Jackson's death.

"This problem is increasingly linked to criminal organisations, like the illegal and massive prescription-drug ring under investigation. It's a serious public health problem."

Toxicology tests during Haim's autopsy did not conclude why the actor died.

Haim's mum, Judy, told Access Hollywood she was told by the LA County Coroner's Office her that her son had an enlarged heart and died of pulmonary congestion, in which his lungs filled up with fluid.

Celebrity gossip website TMZ claims to have been told the Coroner's Office may investigate several urgent care facilities that prescribed medication to Corey Haim.

The law enforcement sources said Haim's mum told Coroner's investigators that her son had been going to numerous urgent care facilities to get prescriptions.

The actor had been struggling with drugs for years.