GULFPORT, Miss. (AP) — Three south Mississippi residents have pleaded guilty to writing unauthorized prescriptions for others, after they and nine others were indicted in June.

Nakita Piernas pleaded guilty Tuesday in federal court in Gulfport to conspiring to distribute drugs outside of professional practice. Tyrone Thomas Jr. and Andrea Opoku pleaded guilty to the same charge earlier this month. All three face up to 20 years in prison and a fine of $1 million.

All three have been named as former employees of Merit Health's Gulf Oaks Outpatient Center in Biloxi.

Of the remaining nine, Marcus Prince pleaded guilty Oct. 17 to the same conspiracy charge. Six others have pleaded guilty this month to either one or two counts of fraudulently obtaining drugs, which carries a sentence of up to four years in prison and up to a fine of $250,000 for each count. Drugs involved include opioids, Xanax, Adderall and Klonopin.

Proof presented last week by prosecutors against Piernas says she began forging prescriptions for friends, now codefendants, in 2014, using blank prescription pads from the clinic. Prosecutors say Piernas wrote two fake prescriptions in her own name that she picked up, and would also lie to pharmacists who called the clinic to verify fake prescriptions written by herself and others. Sometimes, Piernas would take money for the fake prescriptions.

Defendants Beverly Clayton and Thomas Williams have pleaded not guilty and are scheduled for trial in January. All the people who have pleaded guilty are scheduled to be sentenced in January.