FULL CLAIM: “I have three friends. All three of them at stage four cancer. All three of them don't have cancer right now at all […] They took some... what you've heard they've taken [ivermectin and fenbendazole]”
REVIEW
On 9 January 2025, comedian Joe Rogan interviewed actor Mel Gibson for his podcast The Joe Rogan Experience. During the interview, Gibson claimed that three of his friends were cured of late-stage cancer after taking “what you’ve heard they’ve taken”. To Rogan’s question, “ivermectin?” Gibson nodded and added, “fenbendazole”. Rogan went on arguing that “things that do cure you [like ivermectin and fenbendazole] are not promoted because they’re not profitable”.
Rogan’s podcast is extremely popular and has provided a platform to multiple figures that spread misinformation about COVID-19 and other health and climate topics.
Excerpts of the interview containing the claim that ivermectin and fenbendazole cure cancer went viral on social media, gathering millions of views on Facebook (examples here and here), Instagram, TikTok, and X (formerly Twitter). A clip posted on the X account @TheChiefNerd had received over 60 million views at the time of writing.
The claim that fenbendazole treats or cures cancer has circulated online since at least 2019. For its part, ivermectin gained major public visibility during the COVID-19 pandemic after some groups falsely touted it as a COVID-19 cure.
The virality of Gibson’s interview led the Canadian Cancer Society to explain on X:
“Mel Gibson promoted drugs that are not scientifically proven cancer treatments. Misinformation on cancer treatment is dangerous, cruel, irresponsible and gives false hope to people with cancer and their loved ones […] Choosing to use an alternative therapy can have serious health effects, such as the cancer spreading or getting worse.”
Indeed, as Science Feedback and others explained on earlier occasions, there is no scientific evidence supporting the use of ivermectin or fenbendazole for treating cancer. Though both drugs have shown promising effects in laboratory cells and animals, these results don’t demonstrate they are safe and effective for treating cancer in people. We explain in detail below.
Ivermectin and fenbendazole have shown anticancer effects in laboratory experiments but evidence in humans is lacking
Ivermectin and fenbendazole are antiparasitic drugs initially developed for veterinary medicine. Both have shown anticancer effects in laboratory cells and animals, so research about their potential use as cancer treatments is ongoing.
Ivermectin is included in the World Health Organization’s list of Essential Medicines for its effectiveness against several parasitic diseases in humans, including river blindness (onchocerciasis), strongyloidiasis, hookworms, and other diseases caused by soil-transmitted parasitic worms. It is also used to treat scabies.
Ivermectin disrupts the normal functioning of parasites’ muscular and nervous systems, causing their paralysis and death[1]. Researchers found that ivermectin can also disrupt signaling pathways involved in the proliferation of several types of cancer cells cultured in the laboratory[2]. In mice, ivermectin enhanced the efficacy of chemotherapy and immunotherapy drugs against ovarian and breast cancers[3,4].
Based on these findings, clinical trials in humans have begun to evaluate whether ivermectin’s anticancer effects hold true in humans. In 2023, researchers at the cancer center City of Hope started a clinical trial to test the safety and efficacy of ivermectin combined with the immunotherapy drug balstilimab in reducing tumor growth and spread in people with aggressive breast cancers. At the time of writing, the trial was in the recruiting phase.
Fenbendazole is a broad-spectrum dewormer used in animals, including dogs, cats, horses, and livestock. Unlike ivermectin, fenbendazole isn’t approved for human use either by the U.S. Food and Drug Administration (FDA) or by the European Medicines Agency (EMA).
The mechanism of action of fenbendazole differs from that of ivermectin. Fenbendazole interferes with the formation of microtubules, a component of the cytoskeleton that provides structural support to the cells and is essential for their activity and growth. By disrupting microtubules, fenbendazole hampers parasites’ cell division and energy metabolism, causing their death. Science Feedback explained this mechanism in detail in an earlier review.
Cancer cells divide much more rapidly than healthy cells. Therefore, they are also more dependent on forming new microtubules, which makes them particularly susceptible to fenbendazole’s effects.
A 2018 study published in Scientific Reports observed that fenbendazole promoted cancer cell death, reducing tumor growth in cells cultured in the laboratory and in mice[5]. Combined with vitamin A, D, E, K, and B supplementation, fenbendazole has also shown anticancer effects in mice with lymphoma, a type of blood cancer.
Other antiparasitic drugs belonging to the same family as fenbendazole can also inhibit tumor growth in breast cancer cells grown in the laboratory[6] and in mice with pancreatic cancer. However, fenbendazole and other drugs from the same family are poorly soluble in water[7]. This limits its use for cancer therapy, which often involves delivering the drug intravenously within a saline solution.
While the results obtained in cell and animal studies merit further research, they don’t demonstrate that ivermectin and fenbendazole are safe and effective cancer treatments for humans.
Laboratory experiments are an essential first step in the search for new treatments. However, human beings are much more complex than cells growing in Petri dishes. Also, the way our body works differs from common laboratory animals like rodents[8,9].
As a result of these differences, drugs that show promise in cells and animal models often don’t work in humans. A 2024 study published in PLoS Biology found that only 5% of the new therapies tested in animals ever receive regulatory approval for human use[10].
This is why clinical trials are required before any treatment can be recommended to people. In the case of cancer, a 2019 analysis estimated that only 3.4% of the candidate drugs tested succeed in clinical trials[11]. Neither ivermectin nor fenbendazole have been tested as cancer drugs, so their potential benefits and side effects in people with cancer are unknown.
Miracle cancer “cures” are deceptive and potentially dangerous
Products claiming to prevent, treat, or cure cancer are widespread on social media[12]. Some patients turn to such products in the hope that they will be more effective or have fewer side effects than conventional treatments such as chemotherapy and radiation.
But as we explained above, any medical treatment, including cancer treatments, must undergo rigorous clinical trials to demonstrate safety and effectiveness. Online remedies generally lack such scientific validation and provide little to no evidence of whether they are safe and beneficial in people with cancer. These unproven remedies can harm people in many ways.
First, self-medicating with drugs can be dangerous because all drugs come with side effects. The fact that a drug has been approved for treating a disease only means that its benefits for treating that particular disease outweigh the risk of side effects. It doesn’t mean that the drug will automatically be effective for treating other medical conditions. Furthermore, some drugs can cause harm when they’re not used as intended.
For example, ivermectin can cause dangerous interactions with other drugs, like blood-thinner medications. During the COVID-19 pandemic, the U.S. poison control centers saw an increase in calls due to ivermectin overdose, sometimes caused by concentrated veterinary formulations intended for large animals. Symptoms spanned from mild rash, headache, nausea, and vomiting to severe toxicity involving seizures, coma, and respiratory failure.
In the case of drugs that haven’t been approved for use in humans, like fenbendazole, there are often no studies on their effects on people. Therefore, their potential to cause side effects, toxicity, and interactions with other medications in humans is unknown.
Second, even products that aren’t harmful per se can still cause harm indirectly, as some patients may delay or replace effective medical treatment with unproven remedies. Delayed treatment can cause cancer to spread or worsen, reducing a person’s chances of survival[13].
Researchers at the Yale School of Medicine found that people who use complementary and alternative cancer therapies—those used in addition to or instead of conventional treatment, respectively—are more likely to reject medical treatments recommended by their oncologists[14,15]. This is associated with a higher risk of death compared to people who only receive clinically proven treatments.
It is also important to remember that “[t]here isn’t one cure for cancer”, as the American Cancer Society explains. Instead, doctors usually combine different strategies to tailor treatment for each patient. The persistent myth that pharmaceutical companies are hiding the “cure for cancer” because it isn’t lucrative is contradicted by the constant development of new therapies. Current treatment options including surgery, radiation, chemotherapy, immunotherapy, and hormone therapy are safe and effective at stopping cancer from growing and spreading.
But even when treatment succeeds, there is no guarantee that cancer will never come back. That is why oncologists generally use the concept of remission, which means the cancer is under control and causes no symptoms, rather than “cure”.
Therefore, products claiming to “cure” cancer are, in the best-case scenario, deceptive. The FDA urges consumers to “steer clear of these potentially unsafe and unproven products”.
Conclusion
The claim that the antiparasitic drugs ivermectin and fenbendazole cure cancer in humans is unsupported. Currently, ivermectin is only approved for use in humans to treat parasitic infections, and fenbendazole is approved only for veterinary use.
Both ivermectin and fenbendazole have shown promising anticancer effects in laboratory settings. However, clinical data from humans is still lacking. Without that evidence, we can’t know whether these drugs are safe or if they’re able to stop cancer in people. Because of this, they can’t currently be recommended as cancer treatments.
REFERENCES
- 1 – Sulik et al. (2023) Antiparasitic activity of ivermectin: Four decades of research into a “wonder drug”. European Journal of Medicinal Chemistry.
- 2 – Melotti et al. (2014) The river blindness drug Ivermectin and related macrocyclic lactones inhibit WNT‐TCF pathway responses in human cancer. EMBO Molecular Medicine.
- 3 – Kodama et al. (2017) In vivo loss-of-function screens identify KPNB1 as a new druggable oncogene in epithelial ovarian cancer. PNAS.
- 4 – Draganov et al. (2021) Ivermectin converts cold tumors hot and synergizes with immune checkpoint blockade for treatment of breast cancer. npj Breast Cancer.
- 5 – Dogra et al. (2018) Fenbendazole acts as a moderate microtubule destabilizing agent and causes cancer cell death by modulating multiple cellular pathways. Scientific Reports.
- 6 – Graff et al. (2023) Benzimidazole carbamate induces cytotoxicity in breast cancer cells via two distinct cell death mechanisms. Cell Death Discovery.
- 7 – Chang et al. (2023) Anti-cancer effect of fenbendazole-incorporated PLGA nanoparticles in ovarian cancer. Journal of Gynecologic Oncology.
- 8 – Mestas and Hughes. (2004) Of Mice and Not Men: Differences between Mouse and Human Immunology. The Journal of Immunology.
- 9 – Yue et al. (2014) A comparative encyclopedia of DNA elements in the mouse genome. Nature.
- 10 – Ineichen et al. (2024) Analysis of animal-to-human translation shows that only 5% of animal-tested therapeutic interventions obtain regulatory approval for human applications. PLoS Biology.
- 11 – Wong et al. (2018) Estimation of clinical trial success rates and related parameters. Biostatistics.
- 12 – Johnson et al. (2021) Cancer Misinformation and Harmful Information on Facebook and Other Social Media: A Brief Report. Journal of the National Cancer Institute.
- 13 – Hanna et al. (2020) Mortality due to cancer treatment delay: systematic review and meta-analysis. BMJ.
- 14 – Johnson et al. (2018) Complementary Medicine, Refusal of Conventional Cancer Therapy, and Survival Among Patients With Curable Cancers. JAMA Oncology.
- 15 – Johnson et al. (2018) Use of Alternative Medicine for Cancer and Its Impact on Survival. Journal of the National Cancer Institute.
