Jamie Sangouthai -- Lamar Odom's best friend -- did not die from an OD, but it was drug related ... a flesh-eating disease caused by dirty needles.
The exact terms are necrotizing fasciitis -- bacterial skin infection -- and chronic intravenous narcotism -- IV drug abuse ... according to the L.A. County Coroner.
The Coroner says Sangouthai went to the hospital for the infected arm, but the disease spreads quickly and often becomes life-threatening.
Sangouthai -- who appeared with Lamar and Khloe Kardashian on their reality show -- died Sunday at a hospital in Los Angeles. He was 37 years old.