Ivermectin is one of the most important medicines of the last half century. Its discoverers, William Campbell and Satoshi Ōmura, shared the 2015 Nobel Prize in Physiology or Medicine, and it has been given to hundreds of millions of people to prevent river blindness. Since early 2025, interest in ivermectin as a cancer treatment has grown enormously. This article explains how ivermectin acts on cancer cells in laboratory research, which human studies exist, which widely shared studies have been withdrawn, and what is known about its safety and drug interactions.

Part of our guide: Repurposed Drugs for Cancer: A Physician's Guide

What Ivermectin Is

Ivermectin comes from a soil bacterium, Streptomyces avermitilis, found in Japan. It is an approved human medicine for parasitic infections such as river blindness and strongyloidiasis, and it is used on the skin for rosacea and head lice. Unlike fenbendazole, which is made for animals, ivermectin is manufactured to pharmaceutical standards for people, and its behavior in the human body has been studied for decades.

Mebendazole, another approved antiparasitic medicine, has its own body of cancer research; see our article on mebendazole and cancer.

How Ivermectin Acts on Cancer Cells

More than fifty laboratory and animal studies have looked at ivermectin and cancer.¹ A 2020 review from China grouped its actions into several families: blocking growth signals, damaging the cancer cell’s mitochondria, raising oxidative stress, triggering programmed cell death, and acting on cancer stem cells.² The most important findings are below.

1. It blocks the WNT pathway (research from Switzerland)

The WNT–TCF pathway is a master growth switch that is stuck in the “on” position in most colorectal cancers and many others. Researchers in Geneva found that ivermectin and related drugs blocked WNT–TCF signaling in human cancer cells and slowed the growth of human colon cancer grown in mice.³

Our article on your cancer’s driver pathways explains how pathways like WNT are identified in a tumor and why blocking them matters.

2. It shuts down the PAK1–Akt–mTOR growth axis (research from China)

Akt and mTOR are central nodes of the PI3K pathway, one of the most commonly overactive pathways in cancer. In breast cancer, ivermectin broke down a protein called PAK1, which switched off Akt and mTOR and pushed cancer cells into autophagy, a self-digesting state that halted their growth.⁴ In ovarian cancer, the same Akt–mTOR blockade made cancer cells more sensitive to cisplatin, and the combination stopped tumor growth in mice.⁵

3. It weakens androgen signaling and DNA repair in prostate cancer

Prostate cancer depends on the androgen receptor. A 2022 study from China found that ivermectin lowered androgen receptor signaling by acting on a partner protein called FOXA1, and impaired the cancer’s ability to repair its DNA by acting on two repair proteins, Ku70 and Ku80. Ivermectin slowed the growth of human prostate cancer grown in mice.⁶

4. It targets cancer stem cells

Cancer stem cells are a small population of cells that resist chemotherapy and can regrow a tumor after treatment. Researchers in Mexico found that ivermectin preferentially inhibited breast cancer stem-like cells compared with the bulk of the tumor cells.⁷ This is one reason ivermectin draws interest as a possible partner to treatments that shrink tumors but leave stem cells behind.

5. It may make tumors more visible to the immune system

A 2021 study reported that ivermectin caused breast cancer cells to die in a way that alerts the immune system, drawing T cells into tumors in mice and turning immunologically “cold” tumors “hot.” Combined with checkpoint immunotherapy, the effect was stronger.⁸ In June 2026, the journal published an editorial expression of concern about this paper because several image panels were highly similar and the original data were no longer available. The finding has not been disproven, but it now needs independent confirmation.

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How Far Ivermectin Has Been Studied in People

No completed clinical trial has shown that ivermectin improves outcomes for people with cancer. An analysis presented at the European Society for Medical Oncology in 2025 counted at least fifty preclinical studies, no clinical evidence in humans, and one active trial.¹

The trial under way. At Cedars-Sinai Medical Center in Los Angeles, a small early-phase trial is testing ivermectin together with checkpoint immunotherapy (balstilimab or pembrolizumab) in metastatic triple-negative breast cancer, looking at safety, dosing and tumor response. It was recruiting patients as of August 2026.⁹

Our article on triple-negative breast cancer covers the standard and newest treatments for this cancer, and how immunotherapy works explains the checkpoint drugs ivermectin is being combined with.

The National Cancer Institute. In early 2026, the director of the U.S. National Cancer Institute said the institute had undertaken preclinical laboratory study of ivermectin’s ability to kill cancer cells.¹⁰ Results had not been published at the time of writing.

The retracted 2026 cohort. In June 2026, Anticancer Research published a study of 197 cancer patients prescribed ivermectin with mebendazole, reporting an 84.4% “clinical benefit ratio.” The journal issued an expression of concern within days and retracted the paper in October 2026. The editor explained that the benefit figure combined self-reported outcomes that could not be compared with the patients’ condition before treatment, and that the missing clinical information could not be reconstructed. The journal stated that it made no allegation of research misconduct.¹¹ Readers who have seen this study cited should know it has been withdrawn.

The concentration question. Many laboratory studies use ivermectin concentrations higher than those reached in the blood with the standard antiparasitic dose. Researchers disagree about how much this matters, since ivermectin concentrates in some tissues. A dose-escalation study in healthy volunteers found that single doses up to ten times the approved dose were well tolerated.¹² Whether the doses needed against cancer can be given safely over months has not been tested.

Known Side Effects and Drug Interactions

Nervous system toxicity at high doses. At standard doses, ivermectin is kept out of the brain by a transport pump called P-glycoprotein. When blood levels are very high, or the pump is blocked, ivermectin can reach the brain. A 2026 report described a 73-year-old woman with metastatic breast cancer who took high-dose ivermectin on her own after reading cancer claims online and developed confusion, seizures and respiratory failure requiring a ventilator.¹³

Drug interactions. Ivermectin is broken down by the liver enzyme CYP3A4 and moved by P-glycoprotein. Medicines that block either one, including certain antifungals, antibiotics such as clarithromycin, and some HIV medicines, can raise ivermectin levels. Many targeted cancer drugs also use CYP3A4, so combinations deserve careful review. Increases in the blood-thinning effect of warfarin have also been reported.

Loa loa infection. People who have lived in parts of Central and West Africa where the Loa loa eye worm is common can have serious brain reactions to ivermectin if they carry a heavy infection.

Where Ivermectin Fits in an Integrative Approach

Ivermectin’s documented actions fall on pathways that can be measured. A tumor sequencing report may show activation of the WNT pathway or the PI3K–Akt–mTOR pathway; a prostate cancer may still depend on androgen signaling; a cancer may carry a large stem cell population. These are the settings in which ivermectin’s laboratory actions make biological sense. Chemosensitivity testing, which exposes a patient’s own living cancer cells to a panel of drugs and natural compounds, can include ivermectin and report directly whether those cells respond.

A tumor sequencing report shows which of these pathways is active in a particular cancer, and chemosensitivity testing can show whether a patient’s own cancer cells respond to repurposed drugs.

Our book, The New Reality of Cancer, organizes repurposed drugs like ivermectin by the cancer pathways they act on and explains how sequencing and functional testing can be used to match them to a specific cancer.

Frequently Asked Questions

Does ivermectin kill cancer cells?

In laboratory and animal studies, ivermectin slows or kills many types of cancer cells through several pathways. Whether it improves outcomes in people has not yet been shown in a clinical trial.

Is there a clinical trial of ivermectin for cancer?

Yes. A trial at Cedars-Sinai (NCT05318469) is testing ivermectin with immunotherapy in metastatic triple-negative breast cancer.

Was the 2026 ivermectin and mebendazole study retracted?

Yes. The Anticancer Research cohort study published in June 2026 was retracted in October 2026 for methodological and analytical problems.

What is the difference between ivermectin and fenbendazole?

They belong to different drug families and act on cancer cells differently. Ivermectin is an approved human medicine that acts mainly on growth signaling pathways. Fenbendazole is an animal medicine that acts mainly on microtubules and glucose metabolism. Read our article on fenbendazole and cancer.

About the author. Dr. Silver, MD, graduated from Temple University School of Medicine, completed fellowship training in cardiology, and has practiced medicine for nearly fifty years. A lymphoma survivor of about twenty-five years, he is co-author, with Dr. Lindmeier, DHSc, of The New Reality of Cancer: The Science of Recovery. Read more about Dr. Silver, MD.

Research by Dr. Lindmeier, DHSc, cancer educator and co-author of The New Reality of Cancer.

This article is for general education only and is not individual medical advice. Always consult your own doctor before making any changes to your care.

For more in-depth information on this topic and many others, get our book, The New Reality of Cancer: The Science of Recovery.

Explore our guides: Stage 4 Cancer Options · Advanced Cancer Testing · Integrative Cancer Treatment Options · Natural Compounds and Cancer · Repurposed Drugs for Cancer · Cancer Treatment by Type

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