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Demi Lovato refused to tell paramedics what drug caused her to overdose, and law enforcement sources say no drugs were seized at her home.

Law enforcement sources say Lovato was not cooperative when EMTs worked on her at her home Tuesday morning. Those sources believed it was a heroin OD based on what they observed at her home, but a source close to Lovato tells us it was not heroin, though the source refused to divulge what caused the OD.

As we first reported, Demi was unconscious when paramedics arrived and she was brought back to consciousness with Narcan, which is used to counter the effects of opioids.

Our law enforcement sources say there is NO criminal investigation, because they did not seize any drugs and can't determine if Demi was in possession of an illegal substance.