TMZ: DEMI LOVATO Overdose Not From Heroin

Demi Lovato did not OD on heroin .. . so says a source connected to the singer .

TMZ broke the story .. . law enforcement sources involved in the case told us it was an apparent heroin overdose , but the source close to Demi says no .

The source would not reveal what drug caused her to OD, but as we reported she was given Narcan , which is used to counter the effects of opioids .

Lovato had previously struggled with cocaine and Oxycontin addictions but had been clean for 6 years. She recently confessed she fell off the wagon .