The doctors accused of fueling Matthew Perry's fatal addiction are not one-offs ... they are part of an elaborate, secret celebrity drug ring that is running rampant in Hollywood.

TMZ Studios has a new documentary -- "TMZ Investigates Matthew Perry and the Secret Celebrity Drug Ring" -- that airs Monday night at 9 PM ET on FOX and drops Tuesday on Hulu.

Celebrities such as Kelly Osbourne talk frankly about doctors who will gladly fill prescriptions of known addicts to get close to the stars and make lots of money in the process. "Jackass" star Brandon Novak talks about how he traded swag for drugs in doctors offices.

Dr. Drew talks about how some of these doctors are downright sociopathic -- and discusses the dirty little secret of a network of MDs who regularly cross the ethical line ... by a mile.

The documentary exposes a network that also includes various enablers and even rehab centers.