By Katia Hetter, CNN

(CNN) — Ivermectin can now be purchased in Idaho just like Tylenol or ibuprofen, without the need for a prescription, after Gov. Brad Little signed a bill into law that permits the deworming medication to be sold over the counter. Two other states, Arkansas and Tennessee, have passed similar legislation.

I wanted to understand the impetus — and the science — behind the movement to make ivermectin more accessible. What is ivermectin, and what are its approved uses? Why do some people believe that it can be used beyond its approved uses? What are potential harms of taking this medication? And how should someone considering ivermectin approach the decision to use it?

To help answer these questions, I spoke with CNN wellness expert Dr. Leana Wen. Wen is an emergency physician and adjunct associate professor at George Washington University. She previously was Baltimore’s health commissioner.

CNN: What is ivermectin? What are its approved medical uses?

Dr. Leana Wen: Ivermectin is a medication used to treat some parasitic worms. There are two main formulations used in humans. One is a tablet that the US Food and Drug Administration has approved to treat two specific conditions caused by parasitic worms, intestinal strongyloidiasis and onchocerciasis.

Strongyloidiasis occurs when a worm goes in the skin and reproduces in the lungs and intestines. It can cause digestive, respiratory and skin problems; in some people with immunocompromising conditions, it can be life-threatening.

Onchocerciasis, also known as river blindness, is transmitted by repeated bites of infected blackflies that transmit the parasitic worm. In the body, the worm can migrate to multiple organs, including the eye. It can cause vision impairment and eventually blindness; globally, it is the second leading infectious cause of blindness.

Ivermectin can also be used as a cream. Some of these topical forms are approved to treat parasites such as head lice and skin conditions such as rosacea.

Ivermectin is not only used in humans; it is also commonly used as an antiparasitic agent in animals. In dogs and cats, it is licensed as a preventive medication against heartworm. In larger farm animals, including horses and cattle, ivermectin is used as a broad-spectrum medication to treat parasitic infections. The dose for livestock can be many times the dosage for humans.

CNN: Why do some people believe that it should be taken beyond approved uses?

Wen: During the early days of the Covid-19 pandemic, there were a number of medications that had been approved for other purposes that were being studied for their effectiveness against the coronavirus. Ivermectin is not an antiviral medication, but some laboratory studies indicated that high levels of the medication might affect the coronavirus.

That’s why ivermectin, along with a handful of other generic medications such as the antimalarial drug hydroxychloroquine and the antidepressant fluvoxamine, were studied for their efficacy against Covid-19 in rigorous placebo-controlled, double-blind studies, which are the gold standard for researching drug effectiveness.

Ivermectin did not decrease the occurrence of emergency department visits, hospitalizations or deaths associated with Covid-19, according to numerous studies, including several published in The New England Journal of Medicine. Other studies, such as a 2023 report published in JAMA, found no effect in reducing symptom duration or preventing hospitalization, even at higher doses.

Despite these studies, there are individuals, notably some prominent right-wing influencers, who have continued to advocate for ivermectin as a Covid-19 treatment. Some have gone further to recommend that it be used for other diseases, including cancer. Those in favor of making ivermectin over the counter argue that people should not be denied access to what they see as a miracle drug that can cure all kinds of ailments for which the medication is not approved.

CNN: What are potential harms of taking ivermectin?

Wen: Like many medications, ivermectin comes with a long list of potential side effects that include difficulty moving muscles, joint pain, swollen lymph nodes, bloody stools, dizziness, sleepiness and unusual weight gain or loss. There are drug interactions with dozens of medications, including blood thinners, cholesterol-lowering drugs and antiviral treatments.

During the height of the Covid-19 pandemic, US poison control centers reported seeing increasing cases of ivermectin toxicity, including in people who took veterinary formulations that contained high concentrations of the drug. Symptoms of overdose included neurological and gastrointestinal abnormalities. Two people in New Mexico are reported to have died due to ivermectin overdoses. Federal health officials issued repeated warnings that people should not be purchasing ivermectin intended for animal consumption and that it’s a medication that has not been shown to be effective in treating Covid-19.

CNN: Why are states allowing ivermectin to be sold over the counter?

Wen: I think some legislators feel strongly that this medication should be able to be purchased by those who want it, without having to go through the doctor. I have heard some doctors say that they would rather their patients have access to human-dose ivermectin rather than purchasing the formulation intended for animals. Still, this is really quite a departure from how over-the-counter status is determined; in the past, it was federal health authorities, specifically, the FDA, that weigh the scientific evidence and determine whether a medicine is appropriate to be sold over the counter, not on a state-by-state basis by state legislators and governors.

CNN: How should someone considering ivermectin approach their decision?

Wen: Even if ivermectin may be able to be obtained without a prescription in some areas, people should keep in mind that this is still a drug like other drugs. As such, it has conditions for which it is useful and beneficial, but it also has downsides. If it is used to treat conditions that it doesn’t work on, the potential harms will outweigh the benefits. Also, if it is used in place of treatments that are actually effective, that could also cause harm.

To be clear, ivermectin has legitimate — and important — medical uses. Individuals who wish to take it should discuss doing so in consultation with their physician. They should carefully consider the indication for which they are taking it and, as they would for any medication, assess the benefits, risks and alternatives.

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