The rush to find a treatment for COVID-19 has cast a spotlight on the anti-parasitic drug ivermectin, but global health experts have warned that clinical trials were still needed to establish its efficacy.
The oral drug is based on a compound discovered by Omura Satoshi, a Distinguished Emeritus Professor at Kitasato University. He was awarded a Nobel Prize for the discovery.
Ivermectin is widely used to treat parasite-borne infectious diseases, mainly in Africa, while it is also approved in Japan to treat scabies.
A report published last year said cell-based lab experiments have shown that ivermectin can suppress multiplication of the coronavirus.
Some Latin American countries have approved the drug to treat COVID-19 patients. But studies are still ongoing around the world, as its efficacy and safety remain unproven.
In Japan, the Kitasato Institute has been conducting a clinical trial since last September, targeting coronavirus patients with mild to moderate symptoms, with blood oxygen levels of 95 percent of more.
In the US, the National Institutes of Health warned in February that ivermectin is not approved for the treatment of any viral infection.
It said it was impossible to draw definitive conclusions on the clinical efficacy of the drug for COVID-19 treatment. The reasons it cited included the limited sample size of studies, the lack of clarity on the severity of COVID-19 in study participants, and other incomplete information.
Ivermectin's US manufacturer Merck also said in February that there was "no scientific basis" for the drug's potential therapeutic effect against COVID-19.
In March, the World Health Organization advised that ivermectin should only be used to treat patients within clinical trials.
It said data from 16 trials involving 2,407 subjects showed that evidence on whether the drug reduces mortality or quickens improvement was of "very low certainty."
Japan's health ministry's COVID-19 treatment guidelines revised in July places ivermectin in a category of drugs whose efficacy and safety have not been established.
The guidelines refer to reports that the drug does not improve mortality, shorten hospitalization or hasten the reduction of viral loads in patients with mild symptoms.
Liver disorders are among the drug's possible side effects. The manufacturer also said it was unclear whether the product could be safely used among elderly people or pregnant women.
Ivermectin is also given in high doses to animals to treat parasitic diseases. The US Food and Drug Administration said in March that it has received multiple reports of patients who have been hospitalized after self-medicating with ivermectin intended for horses.
The FDA said, "You may have heard it's okay to take large doses of ivermectin. That is wrong." It added that overdosing could cause nausea, diarrhea, seizures or even death.
The FDA ramped up its warning via Twitter in August, saying, "You are not a horse. You are not a cow. Seriously y'all. Stop it."