Pathologist Dr. Roland Kohr performed an autopsy on Haley Bryan, 17, on Jan. 4.
Bryan was pronounced dead at St. Vincent Clay Hospital after she -- and three other teenagers -- allegedly smoked the contents of a Fentanyl patch, which is a drug 100 times more potent than morphine.
Preliminary autopsy results indicated there was no medical reason for Bryan's death.
According to information provided by the Clay County Sheriff's Department Friday, Kohr ruled Bryan's death was due to "pharmacologic intoxication" and there was an undisclosed amount of Fentanyl in her system.
Regarding a recent report about the presence of a second drug in the toxicology report, officials were unable to confirm what the drug was pending verification of Bryan's medical records and any medications she was legally prescribed by a physician.
Because the Health Insurance Portability and Accountability Act (HIPPA) regulations protect the privacy of a patient's medical records and the investigation continues into circumstances surrounding Bryan's death, officials said further details would be limited to protect the integrity of the investigation.