Officials say the arrests were made Thursday during a multi-agency operation called Killer High that included law enforcement from the Fresno Police Department, Fresno County Sheriff's Office, Fresno County District Attorney's Office and the Department of Justice.
The operation was launched after a string of fentanyl-related overdoses occurred in Fresno County.
Authorities say there have been seven fentanyl overdoses in Fresno County, including two deaths. The DOJ said four of those cases involved high school students, and one overdose occurred at a high school.
At least 18 people are now in custody.
Detectives also seized 55,000 fentanyl pills, 2 kilograms of fentanyl powder, a pill press, one pound of cocaine and ten pounds of crystal meth during their takedown of the drug ring.
Several firearms were also confiscated.
WATCH: Killer High: The Silent Crisis
Killer High: The Silent Crisis | Original Documentary