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Sunday 1 October 2023 Dublin: 13°C
FactCheck: Has the drug ivermectin been proven to be effective against Covid-19?
The debate about this anti-parasitic drug continues as experts await results of new studies.

FOLLOWING A RECENT segment on Newstalk’s The Pat Kenny Show, during which an intensive care specialist hailed the benefits of the drug ivermectin, there has been an increase in viral social media posts urging its use in Ireland to treat Covid-19.

The debate about the use of ivermectin is not new, it has been raging online since last year. However it was reignited last week when Dr Pierre Kory, a critical care specialised based in the US state of Wisconsin, spoke to Pat Kenny.

He said that the drug has been “proven” to be effective, but there is a “very strong and deep opposition in public health agencies, in the ivory towers”.

Dr Kory said that while for-profit drugs get exposure and support, there are “attacks” on repurposed  and low-cost drugs such as ivermectin.

Ivermectin is conventionally used to treat parasitic worm infestations and to treat skin conditions such as rosacea. It is also authorised for veterinary use for a wide range of animal species for internal and external parasites.

There have been several studies to examine the potential benefits of this drug as both a treatment and a preventative measure against Covid. However the world’s top health agencies have said there is still insufficient evidence that this medication is effective against Covid. 

Dr Kory claimed during the interview that if the drug’s efficacy was to be recognised, vaccine hesitancy would increase which would go against public health policy and he believes this is one of the reasons for pushback against the widespread use of the drug. He also said there are other oral antiviral medications that large pharmaceutical companies are trying to bring to the market. 

“There’s a massive market of drugs that would be impacted if ivermectin’s efficacy were realised and it would be systematically deployed.”


The drug entered the Covid-19 spotlight in April last year when an Australian study showed that the drug discouraged SARS-CoV-2 from replicating in monkey cells in a test tube. Scientists at Monash University in Melbourne recommended that ivermectin warranted “further investigation for possible benefits in humans”.

They warned, however, that it was unproven in humans.

Since then, there have been multiple human trials but numbers of participants in many of these have been small and experts have subsequently criticised their methodologies.

The European Medicines Agency (EMA), the US Federal Drugs Administration (FDA) and the World Health Organization (WHO) do not support the use of ivermectin in the treatment of patients outside of clinical trials. 

In March this year the EMA said it had reviewed the latest evidence on the use of ivermectin as a Covid treatment.

It noted that laboratory studies found ivermectin could block replication of SARS-CoV-2 in a test tube, but at much higher ivermectin concentrations than those achieved with the currently authorised doses.

“Results from clinical studies were varied, with some studies showing no benefit and others reporting a potential benefit,” it said.

“Most studies EMA reviewed were small and had additional limitations, including different dosing regimens and use of concomitant medications. EMA therefore concluded that the currently available evidence is not sufficient to support the use of ivermectin in Covid-19 outside clinical trials.”

Also in March, The Journal‘s science factchecker Anthony King provided an overview of some of the evidence to date at that juncture. Since then, further data and analysis has emerged. 

Last month, a Cochrane review of 14 studies with a combined 1,678 participants identified the ‘unknowns’ around the use of ivermectin and Covid, including:

  • if it leads to more or fewer deaths 28 days after treatment;
  • if it worsens or improves patients’ condition, assessed by need for ventilation, 28 days after treatment;
  • if it increases or reduces negative Covid-19 tests.

Cochrane is a not-for-profit independent network of researchers, health professionals and patients that gathers and summarises the best evidence from research to help people make informed choices about treatment. 

Its authors said their confidence in the evidence was “very low” because they could only include 14 studies with few participants and few events such as deaths or need for ventilation. The methods also differed between studies and they did not report certain factors such as quality of life. 

“Based on the current very low- to low-certainty evidence, we are uncertain about the efficacy and safety of ivermectin used to treat or prevent Covid-19,” they said.

“The completed studies are small and few are considered high quality. Several studies are under way that may produce clearer answers in review updates. Overall, the reliable evidence available does not support the use ivermectin for treatment or prevention of Covid-19 outside of well-designed randomised trials.”

The WHO has issued guidance on a number of other therapeutic approaches to Covid-19. The latest guidance in July this year strongly recommended the use of IL-6 receptor blockers in patients with severe or critical Covid. In September last year it also recommended the use of systematic corticosteroids in patients with severe and critical Covid illness.

The WHO has strongly recommended against hydroxychloroquine and lopinavir/ritonavir in patients with Covid illness of any severity.

In June this year, Ireland’s Health Information and Quality Authority (HIQA) published its advice to the National Public Health Emergency Team (NPHET) in relation to interventions and preventions for Covid-19.

It found that there is insufficient evidence for any other interventions, aside from Covid-19 vaccines, to prevent Covid-19 or reduce the risk of severe illness. 


In his interview about Covid and ivermectin, Dr Kory referenced “60 controlled trials”.

“Thirty of them are randomised, the randomised control trials have over 3,000 patients in them,” he said.

He added that these trials show “massive reductions in mortality, hospitalisation, time to clinical recovery and also time to viral clearance”.

Though Dr Kory made reference to a number of specific studies, he did not name authors or any scientific journals in which papers were published. tracked down some of these studies to add further context to his claims.

Dr Kory made reference to a trial in Argentina involving healthcare workers, stating that none of the participants who were given ivermectin tested positive for Covid while 50% of those who did not receive it did test positive. 

This trial involved the use of a combination of ivermectin and iota carrageenan, which is a polymer derived from seaweed that has been shown to have antiviral properties which work against viruses such as herpes simplex, dengue and the influenza virus. 

Over a three-month period, healthcare workers at four hospitals in Argentina received the carrageenan nasal spray four times a day and a 12mg dose of ivermectin once a week. 

None of the workers receiving the combination treatment tested positive for Covid during the study, while 58.2% (237) of the workers in the study who were using PPE alone as protection against the virus tested positive over the same period. 

The study did not include separate groups receiving just the nasal spray or just ivermectin and therefore did not provide data on the individual effectiveness of ivermectin in preventing Covid-19 infection.

Dr Kory also discussed a study involving household contacts of positive cases in which 50% of those who did not receive ivermectin got sick while just 7% in group that received ivermectin got sick with Covid-19.

In a study of 304 close contacts of confirmed cases in Egypt, 203 people were given ivermectin while 101 were not. 

 A Cochrane Library review of this trial rated it as being at high risk of bias and stated “confidence in the result is low”. 

Dr Kory used a number of countries as examples of success stories. He referenced the state of Uttar Pradesh in India which began using ivermectin in August 2020.

“They had a surge in April, in May, because of all of the migrant workers coming back from the cities, but they put it down very quickly with aggressive testing and ivermectin use,” he said. 

Dr Kory did not mention that the administration of Uttar Pradesh also introduced lockdown restrictions at the end of April to curb the spread of the virus, extending them a number of times across the entire month of May.

In the Newstalk interview, he also spoke about a ‘test and treat’ programme in Mexico City involving 100,000 people who tested positive for Covid. 

He said of the 50,000 who received early treatment with ivermectin, there was a 60-70% reduction in the need for hospitalisation. 

“They essentially emptied their hospitals in a one to two month period without vaccination,” he said.

Mexico City health authorities did roll out an at-home treatment programme in December 2020 and subsequently published results.

People who had tested positive were sent medical kits which contained ivermectin (four 6mg tablets, two pills to be taken for two days), paracetamol (ten 500mg tablets, one tablet to be taken every eight hours, if symptoms were present) and acetylsalicylic acid [aspirin]  (30 100mg tablets, one pill to be taken daily for 14 days).

This was a non-clinical and non-randomised study which was not peer-reviewed or independently validated.

Authors recognised there were a number of limitations, including that the comparison groups likely had differences in variables. They also acknowledged that at the time hospital occupation was very high, with poor availability of beds and this could explain the lack of hospitalisation in some patients who actually require it. 

Media reports in January, during which this study was running, detailed intense pressure at hospitals in Mexico city due to Covid, with the government stating that hospitals were at 90% capacity.

The study has been widely characterised as misleading, according to Brazilian factchecking site Estadão Verifica because it heavily emphasised ivermectin in its results, though that drug was one of three included in the kit and was only taken over a period of two days. 


Trinity College graduate Professor William Campbell, who shared the Nobel Prize in Physiology/Medicine in 2015 for the discovery of ivermectin, has described the chances of ivermectin being used safely to kill the virus in people as low.

However he said it was still worth pursuing this as a potential treatment. 

And studies into its efficacy are continuing. 

In June this year, the University of Oxford said it was beginning an investigation into the use of ivermectin as a possible treatment for Covid. The study had so far recruited more than 5,000 volunteers from across the UK.

Also speaking to Newstalk’s Pat Kenny this week, immunology and biochemistry professor Luke O’Neill said there are two major trials ongoing and these should help to provide answers but “the jury is still out” on the studies that have been done to date. 

“If it works it will be great of course,” he said. “It is very cheap, it has been used for parasitic diseases, it is safe in humans – it has all the right things going for it.

“But the truth is, if you look at all the data combined, the jury is still out and we need more evidence to support it.

“There is some evidence out there absolutely. Several groups have looked at all of the data combined and there might be something going on but there are two massive trials running at the moment which is fantastic because it will really test it one way or another.

“At the moment, in my view and in the view of many people looking at this, the jury is out still sadly but if it works, it will be great.”


Several studies have claimed to show ivermectin is an effective treatment or preventative medication for Covid. However these studies have been branded as unreliable or inconclusive and all major health agencies have warned against its use outside clinical trials.

Experts and health bodies have not expressed opposition to researching potential benefits of ivermectin as a therapeutic approach to the disease and further research in this area, including larger high quality studies, are coming down the pipeline. 

Based on the current available research, ivermectin has not been proven to play a significant role in the prevention of Covid-19 infection or a reduction in the severity of symptoms. 

We rate the claim that ivermectin has been proven to be effective against Covid-19 UNPROVEN.’s FactCheck is a signatory to the International Fact-Checking Network’s Code of Principles. You can read it here. For information on how FactCheck works, what the verdicts mean, and how you can take part, check out our Reader’s Guide here. You can read about the team of editors and reporters who work on the factchecks here.

- With reporting by Anthony King.