LITTLE ROCK, Ark. (AP) — The Arkansas Medical Board is investigating reports that inmates at a county jail were prescribed the anti-parasitic drug ivermectinto combat COVID-19 even though it hasn’t been approved to treat the coronavirus.

Board Director Amy Embry on Thursday declined to elaborate on the panel’s investigation, which she said began in the last two days. Embry said the investigation came in response to multiple complaints related to news reports about the use of ivermectin at the Washington County jail.

Washington County’s sheriff confirmed Tuesday night that jail inmates had been prescribed ivermectin, but did not say how many. It wasn’t clear if all the inmates who were prescribed the medication had tested positive for COVID-19.

“There is an open investigation and we can’t comment on it right now,” Embry told The Associated Press.

Dr. Rob Karas, the jail’s physician, has said no inmates were forced to take the drug.

The U.S. Food and Drug Administration has approved ivermectin for use by people and animals for some parasitic worms, head lice and skin conditions. The FDA has not approved its use in treating or preventing COVID-19 in humans. According to the FDA, side effects for the drug include skin rash, nausea and vomiting.

“Using any treatment for COVID-19 that’s not approved or authorized by the FDA, unless part of a clinical trial, can cause serious harm,” the FDA said in a warning about the drug.

Embry declined to say who was the target of the board’s investigation. The board has authority over physicians, but not jail facilities.

Sheriff Tim Helder did not return a message Thursday, and a spokesperson for the sheriff’s office did not immediately respond to questions about the drug’s use.

In a lengthy statement released to the AP Thursday, Karas defended the use of ivermectin to treat COVID-19. Karas said he has prescribed it to inmates and patients at his clinics who are significantly sick with COVID-19 since late 2020. He did not respond to questions about the investigation and the number of inmates who have have been prescribed the drug.

“I do not have the luxury of conducting my own clinical trial or study and am not attempting to do so,” Karas wrote. “I am on the front line of trying to prevent death and serious illness.”

The Northwest Arkansas Democrat-Gazette reported that the sheriff’s office said Helder had learned of the drug’s use at the jail on Tuesday. In a July 20 email to Helder, Karas recommended the sheriff’s staff take it as a preventive measure against COVID-19 but did not mention its use on inmates. Karas has said he’s taken the drug, as have members of his family.

Pharmacy prescriptions for ivermectin have been booming this summer, reaching more than 88,000 prescriptions two weeks ago – 24 times the normal weekly number. Calls to poison control centers about ivermectin overdoses have also multiplied, to five times higher than normal, U.S. health officials say. Health officials in Arkansasand Mississippithis week warned people to not take the veterinary formulation of the drug after seeing an uptick in calls to their poison control centers.

The Centers for Disease Control and Prevention on Thursday sent an alert about the trend to doctors. The CDC said there is not good evidence that ivermectin is effective at preventing or treating COVID-19, and that the government has not authorized it to be used against the coronavirus.

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AP Medical Writer Mike Stobbe in New York contributed to this report