Early studies in cell cultures seemed to indicate that ivermectin could prevent COVID-19 from entering cells, but that has not panned out in humans, Hendrickson said.

Yet, the drug continues to be touted by those who oppose COVID-19 vaccines, even though no proof exists that it is effective in preventing or treating COVID-19, he said.

For the study, Hendrickson’s team reviewed ivermectin-related calls to the Oregon Poison Center in August. In all, 21 people reported side effects after taking the drug.

Most of the reports came from people over 60 years of age. Eleven of the reports were from people who took ivermectin to prevent COVID-19. The other 10 took the drug to treat COVID-19 symptoms.

Among those taking ivermectin, three had a prescription from a doctor or veterinarian, and 17 purchased veterinary versions of the drug. Where the others got the drug isn’t known.

For most people, adverse symptoms developed within two hours after taking a large, first-time dose of the drug. In six people, symptoms developed over several days to weeks after repeated doses taken every other day or twice weekly. One person was also taking vitamin D to treat or prevent COVID-19.

Six of the 21 were hospitalized for toxic effects from ivermectin, and all said they took the drug to prevent COVID-19, including the three who had a prescription for the drug.

Of the six hospitalized, four were treated in an intensive care unit, and none died. Among those hospitalized, gastrointestinal distress, confusion, ataxia, weakness, low blood pressure and seizures were the most common adverse side effects.

For those not hospitalized, the most common symptoms were gastrointestinal distress, dizziness, confusion, vision symptoms and rash, the researchers found.

Hendrickson noted there isn’t any treatment for the side effects of ivermectin. “It’s just a matter of waiting and supportive care,” he said.

Since August, reports of serious side effects from ivermectin have continued, although not as many, Hendrickson said.

Dr. Robert Glatter, an emergency medicine physician at Lenox Hill Hospital in New York City, said, “Simply put, there is no clinical use for prescribing ivermectin to treat or prevent COVID-19. It’s irresponsible and frankly dangerous for health care professionals to even consider prescribing ivermectin for treatment or prevention of COVID-19.”