When is ivermectin safe for humans and other questions about anti-parasitic drug not recommended for COVID-19

An anti-parasitic medicine called ivermectin is facing a shortage in Canada amid unproven claims that it can be used to treat COVID-19 — and confusion about the drug has sparked a lot of questions.

Federal agencies are warning people not to take the medication to treat disease caused by coronavirus

Empty ivermectin boxes sit on the shelves of Lone Star Tack & Feed Inc., located just outside Calgary in late August 2021. Alberta feed stores say they're receiving a deluge of callers asking to buy ivermectin due to misinformation that suggests the livestock dewormer can be used to treat COVID-19 in humans. (Lone Star Tack & Feed Inc.)

An anti-parasitic medicine called ivermectin is facing a shortage in Canada amid unproven claims that it can be used to treat COVID-19 — and confusion about the drug has sparked a lot of questions.

Developed in the 1970s, ivermectin is used to treat parasites, such as intestinal worms or lice, in animals and humans.

But early studies exploring its effectiveness as an anti-viral medication that could be used to treat COVID-19 have been used to fuel misinformation — despite being deemed low-quality and robustly debunked by federal health agencies.

WATCH | Feed shops see demand for ivermectin despite health warnings:

Feed shops see demand for ivermectin despite health warnings

2 years ago
Duration 1:58
Featured VideoFeed shops have seen increased demand for ivermectin, commonly used to deworm livestock, to treat or prevent COVID-19, despite health warnings that it doesn’t work and isn’t safe for human consumption.

"The body of evidence that we now have … is that it is not effective in the context of COVID — either for preventing or for treating. The evidence simply does not support it," Tim Caulfield, a professor and the Canada Research Chair in health law and policy at the University of Alberta, said Monday on CBC's The Homestretch.

"[But] we're seeing the popularity of the drug increase, and also, there's been an increase in poisoning and an increase in prescription. It's a really bizarre phenomenon."

So, what is ivermectin and how is it used? Can it help to treat COVID-19? And why are federal agencies like Health Canada and the U.S. Food and Drug Administration warning people not to take it? 

Here are some frequently asked questions about ivermectin answered.

When is ivermectin safe for human use?

Ivermectin is safe for human use when prescribed and dosed by a health-care professional to treat parasitic infections.

Dosage is based on the patient's weight, medical conditions and response to the drug.

The form of the drug used on humans won the Nobel Prize, has improved the health of millions and helped to eradicate diseases like river blindness in multiple countries.

A teacher administers an anti-parasite tablet to a student at a government school as part of national deworming campaign in Hyderabad, India, on Feb. 9, 2018. There is a shortage of ivermectin, an anti-parasite drug needed to treat immigrants to Canada from countries prone to illnesses caused by tropical parasites because of misinformation that the drug can treat COVID-19. (Mahesh Kumar A./The Associated Press)

It is on the World Health Organization's list of essential medicines because it is inexpensive and effective — and has proven to be life-saving for treating some illnesses caused by parasites.

The form of ivermectin intended for humans can also pose risks. Even for approved uses, ivermectin can interact with other medication or be inappropriate for people with certain health conditions — that's why it's best used with a doctor's prescription.

How is the ivermectin used to treat livestock different?

Ivermectin products for veterinary use are dosed for larger animals, like horses or cows, which weigh a lot more than a person. For example, a horse can weigh between 380 and 1,000 kilograms.

Ivermectin products for animals have a higher concentrated dose than ivermectin products for people, Health Canada says.  (CCO/Pexels)

This means that ivermectin products for animals have a higher concentrated dose than ivermectin products for people, Health Canada says. 

Some veterinary drugs may also contain different ratios of medication than the human versions and may go through different testing.

So, what could happen if I take ivermectin improperly?

The veterinary version of ivermectin, especially at high doses, can be dangerous for humans, Health Canada says.

It may cause serious health problems such as vomiting, diarrhea, low blood pressure, allergic reactions, dizziness, seizures, coma and even death.

"Canadians should never consume health products intended for animals because of the potential serious health dangers posed by them," Health Canada said.

In the U.S., the Centers for Disease Control warned the public after increased calls to poison centres with reports of severe illness caused by the medicine.

Last week, the U.S. Food and Drug Administration (FDA) also reissued warnings about ivermectin in response to a growing volume of misinformation on social media, along with reports of people being poisoned and requiring hospitalization after taking it. 

"You are not a horse. You are not a cow. Seriously, y'all. Stop it," said a tweet from the U.S. FDA.

Can ivermectin be used to treat COVID-19?

First of all, ivermectin is used to treat parasites. COVID-19 is caused by a virus.

Some early studies appeared to show promise for its use as an anti-viral as well as an anti-parasitic — with hope that further study could prove it inhibits the growth of the novel coronavirus in human cells and improve patient outcomes.

Those results have not panned out in larger, higher quality studies, which have yet to prove whether ivermectin can slow or stop the novel coronavirus from growing in human cells.

After reports that some people were taking the veterinary form of the medicine intended for livestock, Health Canada issued an advisory on Tuesday asking people not to take the drug to treat COVID-19.

"There is no evidence that ivermectin in either [the human or veterinary] formulation is safe or effective when used for those purposes," it said.

Health Canada says it's closely monitoring all potential treatments for COVID-19, including ivermectin.

"Should a manufacturer provide a submission to Health Canada related to the use of ivermectin to prevent or treat COVID-19, Health Canada would conduct a scientific evaluation of the evidence to determine the drug's quality, safety and effectiveness," the agency said. 

But so far, ivermectin is only approved for use to treat parasites in Canada — not COVID.

A full list of drugs and vaccinations authorized for the treatment or prevention of COVID-19 is available on Health Canada's website. 

But I read, or heard about, studies that suggested it was effective in treating COVID-19. What gives?

Dr. Lynora Saxinger, an infectious disease specialist at the University of Alberta, told CBC News that early studies of ivermectin's use either as a COVID-19 treatment or prevention consisted of low-quality data.

A review published in April in the Cochrane Database of Systematic Reviews concluded that the efficacy and safety of ivermectin to treat or prevent COVID‐19 is unproven.

"The completed studies are small and few are considered high quality. Several studies are underway that may produce clearer answers in review updates. Overall, the reliable evidence available does not support the use of ivermectin for treatment or prevention of COVID‐19 outside of well‐designed randomized trials," it determined. 

One issue was that in some initial positive reports, patients were receiving multiple medications, so the effect of ivermectin couldn't be parsed out. Another was that extremely high doses that showed promise in test tubes didn't translate to human subjects.

Some studies or systematic reviews also consisted of small sample sizes.

WATCH | Horse medication ineffective against COVID-19, says specialist:

Horse medication ineffective against COVID-19, says specialist

2 years ago
Duration 1:10
Featured VideoEpidemiologist Dr. Christopher Labos says getting vaccinated is a safer and better way to protect against the coronavirus. (Benoit Tessier/Reuters)

Medical journal The Lancet has called for more study on ivermectin's efficacy to reduce SARS-CoV-2 viral load or improve recovery — but said there is no drug that can replace preventative public health policies and large-scale testing for COVID. 

Merck, the initial manufacturer of ivermectin, confirmed its scientists have found no scientific basis for ivermectin's efficacy against COVID-19, also citing a concerning lack of safety data in most studies. 

And Alberta Health Services says its scientific advisory group has conducted a review to explore using ivermectin, but the drug is not approved to treat COVID-19 in the province.

It advises against taking ivermectin as a COVID-19 treatment outside of clinical trials.

So, why was ivermectin suggested as a treatment when it's unproven?

It started in November 2020, when a study was published in Egypt suggesting ivermectin could improve outcomes for COVID-19 patients. 

It was the largest study in favour of the drug — but this summer it was retracted after concerns about data fabrication, plagiarism and ethical breaches. 

Before it was retracted, it prompted doctors in some countries to start using the drug just to see what would happen, because it's easily available and inexpensive.

The retracted study also sparked buzz, especially with one right-wing group known for spreading medical misinformation called America's Frontline Doctors, which has been charging patients for consultations to access ivermectin.

In December 2020, Dr. Pierre Kory, who has been an outspoken advocate for ivermectin, called it a miracle drug before a U.S. Senate hearing on COVID-19 treatments. Kory has since said he regrets using that hyperbolic term. 

An article on ivermectin's use in treating COVID, written by the Front Line COVID-19 Critical Care Alliance, which counts Kory among its members, was removed from the journal Frontiers in Pharmacology after editors determined it contained unsubstantiated claims and violated its editorial policies. 

But all that hasn't stopped a number of politicians and media figures from touting the drug as a possible treatment, prevention or cure. 

What's the bottom line?

Ivermectin has not been proven to effectively treat COVID-19, and it can be dangerous when taken in high doses or without the guidance of a health-care professional.

With files from Sarah Rieger and Karin Larsen