Ivermectin as a Cancer Treatment: Does It Work?

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On July 7, 2025

During the COVID-19 pandemic, the antiparasitic drug ivermectin surged in popularity as a potential treatment for coronavirus infection. Large-scale clinical studies eventually concluded that ivermectin did not keep people with COVID-19 out of the hospital, but social media postings about ivermectin’s curative powers — and not just for COVID — have continued to proliferate.

Some people are sharing their views that ivermectin can treat cancer.

Earlier this year, the actor-director Mel Gibson claimed on an episode of The Joe Rogan Experience podcast that ivermectin, in combination with another antiparasitic drug called fenbendazole, saved three friends from stage 4 cancer. “This stuff works, man,” Gibson said.

Researchers have been exploring ivermectin as a possible cancer drug, but they emphasize that the findings are preliminary, and there have been no studies in humans that have found ivermectin to be safe and effective for people with cancer, either alone or in combination with other medications.

Ivermectin Research Is in Early Stages

Scientists suspect that there could be a role for ivermectin in cancer treatment but likely as a helper to cancer drugs with proven effectiveness, says Aaron Schimmer, MD, PhD, director of the research institute at the Princess Margaret Cancer Centre in the University Health Network in Toronto.

More than a decade ago Dr. Schimmer and his team studied the impact of ivermectin on leukemia cells in a laboratory. They found that the drug caused the cells to swell and die.

But Schimmer says that the research never advanced to human clinical trials. “It would be not wise, and probably irresponsible, for physicians to recommend the use of ivermectin based on research that has not been tested on humans,” he says.

Another study, conducted at the City of Hope cancer research and treatment center in Los Angeles and published in 2021, looked at the effect of ivermectin in combination with a type of immunotherapy cancer drug called a checkpoint inhibitor anti-PD1 antibody.

The research found that, in mice, this drug combo triggered the production of a type of protective immune cell called a T cell, generating a response strong enough to stop tumor growth.

Peter P. Lee, MD, coauthor of the study and chair of the department of immuno-oncology at City of Hope, says that a small human trial based on this research is underway and still enrolling people who have metastatic triple-negative breast cancer, an aggressive type.

Preliminary results of the trial, which Dr. Lee and his colleagues presented at this year’s American Society of Clinical Oncology meeting, found that of the eight people with cancer evaluated, one had stable disease, one had a partial response, and the cancer progressed in the other six patients.

Lee is hopeful about a future in which ivermectin may be incorporated into immunotherapy cancer treatment. “As a stand-alone, ivermectin is not a miracle drug for cancer,” he says. “Our ongoing work is about optimizing the [drug] regimen. The way you give [the medications], the timing, the intervals — it all matters a lot. It’s not at all so simple that all you have to do is take the pills. It’s much more complex.”

Is There Any Harm in Taking Ivermectin for Cancer?

It’s understandable that someone with cancer will want to treat themselves with untested drugs if they don’t have access to appropriate medical care or if traditional therapies aren’t working.

But Schimmer cautions against people taking ivermectin on their own, especially at levels higher than the U.S. Food and Drug Administration (FDA) has deemed safe for approved uses. (The FDA has approved ivermectin tablets to treat people with two conditions caused by parasitic worms: intestinal strongyloidiasis and onchocerciasis, also known as river blindness.)

“You can do more harm than good,” Schimmer says. “You may actually shorten life or impair quality of life by producing untoward side effects.”

According to the FDA, an overdose of ivermectin can cause nausea, vomiting, diarrhea, hypotension (low blood pressure), allergic reactions (itching and hives), dizziness, ataxia (problems with balance), seizures, coma, and even death.

Schimmer is concerned that people with cancer are taking big doses of ivermectin anyway. Access to ivermectin is becoming easier in much of the United States because an increasing number of states permit people to buy the drug at pharmacies without a doctor’s approval.

“I think it’s highly unlikely that most responsible physicians would prescribe ivermectin off-label for malignancies where there’s really no evidence of effectiveness,” Schimmer says.

The Future of Cancer Treatment

Although human studies on ivermectin’s effect on cancer are still limited, people interested in contributing to research can look for opportunities to enroll in clinical trials.

Trials offer medically supervised ways to try promising experimental therapies for many different types of cancer, at every cancer stage.

Websites for the National Cancer Institute, the Alliance for Clinical Trials in Oncology, and the ECOG-ACRIN Cancer Research Group offer information on what’s involved in taking part in a trial, plus searchable databases of trials actively looking for participants.