Hayden Panettiere Death: Narcan Found in Apartment

Hayden Panettiere, or someone close to her, was treated with meds typically used for overdose victims ... TMZ has learned.

We've confirmed, through sources in Greenville, SC, that Narcan was found in the apartment where she died. Narcan is administered nasally to reverse the effects of an opioid overdose, and we're told the device used to dispense it was found on a mattress.

We know first responders on the scene mentioned an "overdose" and CPR efforts while reporting back to dispatch.

However, we also know 2 ambulances rushed to the apartment, which seems to point to 2 people in distress in the apartment ... so, it's unclear who received the dose of Narcan.

We're also told epinephrine was used on the scene, and that would track with the initial 911 call being for a woman in cardiac arrest. Epinephrine, aka adrenaline, is commonly used to resuscitate patients in cardiac arrest.

As we reported ... Hayden was pronounced dead on the scene Sunday at 2:32 PM, and no one was transported in either of the ambulances.

We're told Hayden's longtime on-and-off boyfriend Brian Hickerson had been staying at the residence as well. He actually grew up in the area, but we haven't been able to reach him since we first reported Hayden's death.

We spoke to Hickerson back in May, and although he gushed about Hayden, he admitted she'd be better off without him and said he wanted to see her flourish.