Jason Davis Death Case Looks Like Possible Heroin Overdose

Jason Davis' death has authorities thinking he might've overdosed on heroin -- a drug he'd been addicted to in the past and once kicked ... TMZ has learned.

Law enforcement sources familiar with the investigation tell us ... Jason was found unresponsive in his bathroom Sunday morning around 10:30 AM. We're told there were items nearby that were consistent with heroin or opioid use -- including burnt tin foil and other paraphernalia.

An official cause has yet to be determined -- we're told an autopsy and toxicology analysis still needs to be conducted, but for now ... authorities are treating his death as a possible OD.

It makes the situation all the more tragic, as Jason had battled addiction ... and in 2011, he was even arrested and charged for allegedly having heroin on him.

Those charges were eventually dropped after he completed a drug diversion program. About a year before that, he'd been featured on "Celebrity Rehab with Dr. Drew," where he attempted to get clean. We got him on camera around the time his criminal case was being worked on, and he talked sobriety with us -- saying at the time he'd been off drugs for almost a week.

Jason went on to cofound a charity called Cure Addiction Now, which he's said to have been heavily involved with running.

Jason was most known in Hollywood as the voice of Mikey Blumberg on the long-running Disney Channel show, "Recess." He'd acted in several other movies and shows as well.

The guy was just 35.

RIP.