Health officials warn people not to treat Covid with a drug meant for livestock.

Ivermectin, an anti-parasitic drug commonly used for livestock, should not be taken to treat or prevent Covid-19, the Food and Drug Administration said on Saturday.

The warning came a day after the Mississippi State Department of Health issued a similar statement in response to reports that an increasing number of people in Mississippi were using the drug to prevent a Covid infection.

Some studies last year spurred use of the drug against Covid-19, especially in Latin America, and Fox News has promoted some of those studies’ findings on air.

But the National Institutes of Health said in February that most of the studies related to Ivermectin and the coronavirus “had incomplete information and significant methodological limitations,” including small sample sizes and study outcome measures that were often unclear.

In Mississippi, where only 37 percent of the population is fully vaccinated, more than two-thirds of recent calls placed to the state’s poison control center were related to “ingestion of livestock or animal formulations of Ivermectin purchased at livestock supply centers,” the state department of health said in a news release.

Of those who called about ingesting Ivermectin, 85 percent had mild symptoms and one person was told to “seek further evaluation” because of the large amount they were reported to have taken, the state’s health department said.

Ivermectin, which is also formulated for use by people to treat parasitic worms, had been controversially promoted as a potential Covid treatment earlier in the pandemic, but recent studies found that the drug’s efficacy against the coronavirus is thin, and the F.D.A. has not approved the drug for Covid treatment.

On Twitter, the F.D.A. was more declarative in its warning.

“You are not a horse,” the agency said. “You are not a cow. Seriously, y’all. Stop it.”

The F.D.A. said it has received multiple reports, including some in Louisiana, of people who have “required medical support and been hospitalized after self-medicating with ivermectin intended for horses.”

“Taking large doses of this drug is dangerous and can cause serious harm,” the F.D.A. said.

The Mississippi State Department of Health alerted its residents that “animal drugs are highly concentrated for large animals and can be highly toxic in humans.”

Some of the symptoms associated with Ivermectin toxicity include rash, nausea, vomiting, abdominal pain, neurological disorders and potentially severe hepatitis that could require hospitalization, Mississippi health officials said.

Mississippi, which has seen a surge in cases recently, reported 5,048 cases on Friday. Hospitalization and death rates have also been rising.

CAM