Tyler Sanders' death is being treated as a suspected overdose ... sources connected to the death investigation tell TMZ.
We're told Tyler, who had roles in big shows like "9-1-1: Lone Star" and "Fear the Walking Dead," had a history of drug use and cops found a plastic straw and white powder in the room where he died.
TMZ broke the story ... 18-year-old Tyler was found dead June 16 in his Los Angeles home.
Our sources say Tyler's friends called police to conduct a welfare check because they had not heard from him following a night out ... and that's what led to his body being discovered.
Tyler was laid to rest in Houston ... and someone who attended the funeral tells us Tyler's dad, David Sanders, delivered the eulogy and told the crowd Tyler died of an apparent drug overdose.
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We're told Tyler started battling depression when he began filming '9-1-1' and his father repeated some of Tyler's own words at his funeral, talking about how Tyler's brain was wired to where he could not feel happiness.
An official cause of death for Tyler will be determined by the coroner once toxicology reports come back in 4 to 6 months.