Matthew Perry Autopsy, Initial Tests Negative for Fentanyl and Meth

Matthew Perry's death was not the effect of a fentanyl or meth overdose, at least that's what initial tests indicate ... TMZ has learned.

Law enforcement sources tell TMZ investigators ran a less-in-depth test on Perry which revealed he did not have fentanyl or meth in his system. However, it's important to note, more in-depth tests are still being conducted as part of toxicology to analyze whether any other illegal drugs present in his blood -- and if the levels of any prescription meds were at harmful doses.

Those results will likely take anywhere from 4-6 months to be returned, and once all that data is gathered, the coroner will determine the cause and manner of death.

As we first reported, the prescription drugs found in Matthew's house were all prescribed to the actor for his various ailments, and stored in proper bottles.

If something illicit were to come back in his autopsy results, LAPD's Robbery Homicide Division would continue to investigate.

RHD's involvement initially had people scratching their heads, especially as there's currently NO evidence of foul play ... however, it's common for detectives from that division to take the lead on high-profile cases because of its experience and dedicated manpower.

As TMZ first reported, Matthew was found unresponsive in his hot tub Saturday at his home in the Pacific Palisades after playing pickleball for a couple hours earlier that day at Riviera Country Club.

While it appears he died from drowning, the Coroner will have the official word, once all the testing is complete.