Ivermectin, Fenbendazole and Mebendazole in Colorectal Cancer: A 2026 Evidence and Safety Review

Medically Reviewed by: OneDayMD Editorial Team | Evidence Synthesis & Safety Review | Last Updated: July 2026

Quick Answer

No randomized controlled trial has shown that ivermectin, fenbendazole, or mebendazole cure colorectal cancer in humans. The strongest human evidence is a small, 40-patient randomized trial (Hegazy et al., 2022) in which mebendazole added to standard bevacizumab/FOLFOX4 chemotherapy improved response rates as an adjunct — not a replacement. In May 2026, the American Society of Clinical Oncology (ASCO) issued a formal Clinical Notice recommending against using ivermectin or fenbendazole for cancer treatment outside of a registered clinical trial, citing insufficient evidence and a real risk of toxicity and drug interactions. The hundreds of "case report" testimonials circulating on social media are self-reported, unverified, and not equivalent to clinical trial data. This article separates what is actually established from what is anecdotal, and outlines the safety questions patients should raise with their oncology team before considering any of these agents.

Abstract

Background:	Ivermectin and the benzimidazole anthelmintics fenbendazole and mebendazole have attracted sustained public interest as repurposed anticancer agents in colorectal cancer (CRC), driven substantially by social media case testimonials rather than clinical trial publication.
Objective:	To separate verified preclinical and clinical evidence from anecdotal online reporting, to summarize the current mainstream oncology position, and to outline the safety considerations relevant to patients and clinicians encountering this topic.
Methods:	Narrative synthesis of peer-reviewed in vitro, case-report, and randomized trial literature on ivermectin, fenbendazole, and mebendazole in colorectal and gastrointestinal cancer, cross-referenced against the American Society of Clinical Oncology's May 2026 Clinical Notice and published safety case reports.
Results:	Preclinical data support several plausible anticancer mechanisms (Wnt/β-catenin inhibition, microtubule disruption, chemosensitization). Human evidence is limited to one small placebo-controlled trial of mebendazole (n=40) showing improved response and progression-free survival as a chemotherapy adjunct, a small number of published case reports, and early-phase trials of ivermectin combined with immunotherapy that remain in progress. No trial has evaluated these agents as monotherapy replacements for guideline-based CRC treatment. Published safety literature also documents at least one case of drug-induced liver injury following unsupervised self-administration of fenbendazole based on social media information.
Conclusions:	The preclinical rationale is real and worth continued clinical trial investment, particularly for mebendazole. The clinical evidence is not yet sufficient to support use outside of a trial, and ASCO has said so explicitly. Patients considering these agents should do so only in full communication with their oncology team, never as a substitute for standard-of-care therapy, and never sourced from veterinary formulations intended for animals.
Keywords:	ivermectin, fenbendazole, mebendazole, colorectal cancer, drug repurposing, Wnt signaling, ASCO clinical notice

Table of Contents

1. Why This Topic Keeps Coming Up
2. The Pharmacological Rationale
3. Evidence Hierarchy: What Kind of Proof Is This?
4. The Actual Human Clinical Trial Data
5. The Social Media Case-Report Phenomenon
6. ASCO's May 2026 Clinical Notice
7. Safety Considerations Patients Overlook
8. Evidence-Based Adjuncts Worth Discussing With Your Oncologist
9. If You're Considering This: A Practical Framework
10. Frequently Asked Questions
11. Conclusion
12. References

1. Why This Topic Keeps Coming Up

Colorectal cancer (CRC) remains the second-leading cause of cancer death in the United States overall, and the leading cause of cancer death in adults under 50. The American Cancer Society projects roughly 158,850 new CRC diagnoses and 55,230 deaths in the U.S. in 2026, with incidence rising by about 3% per year in adults aged 20–49 even as rates continue to fall in older adults. That combination — a common, deadly disease increasingly affecting younger patients, with a treatment path that still relies heavily on chemotherapy and surgery — is exactly the environment in which patients go looking for anything that might improve their odds.

Ivermectin (an antiparasitic approved for human use against specific parasitic infections) and the benzimidazoles fenbendazole and mebendazole (anthelmintics developed to kill worms, not tumors) have been proposed as repurposed anticancer agents since a Johns Hopkins glioblastoma study first drew attention to benzimidazole antitumor activity in 2009. Interest accelerated sharply after 2019, when a lung cancer patient's fenbendazole self-treatment account ("the Joe Tippens protocol") went viral, and again after 2020–2023, when ivermectin's COVID-era notoriety carried over into an active online community promoting it for cancer.

This review exists because the gap between what circulates online and what has actually been tested in humans is large, and because that gap has real consequences — including at least one published case of liver injury from unsupervised self-treatment (see Section 7). The goal here is not to dismiss the underlying pharmacology, some of which is genuinely interesting, but to give patients, caregivers, and clinicians an accurate picture of where the evidence actually stands in mid-2026.

2. The Pharmacological Rationale

Several laboratory-based (in vitro and animal) studies support biologically plausible anticancer mechanisms for these drugs. None of these findings has yet been confirmed to translate into a proven human treatment benefit, but they explain why the hypothesis has attracted legitimate scientific attention.

Ivermectin

• Wnt/β-catenin pathway inhibition: Wnt signaling (named for the "Wingless" and "int-1" genes originally identified in fruit flies and mouse mammary tumors) is one of the central drivers of colorectal tumorigenesis. In vitro work has suggested ivermectin can interfere with this pathway (Loftalizadeh et al., 2022).
• Direct antiproliferative effect: Zhou et al. (2021), published in a peer-reviewed oncology journal, reported that ivermectin dose-dependently inhibited colorectal cancer cell growth in laboratory models, proposing it as a candidate for further anticancer investigation.
• Chemosensitization: Jiang et al. (2019) reported that ivermectin enhanced the cytotoxic effect of chemotherapy agents in drug-resistant cancer cell lines via EGFR/ERK/Akt/NF-κB signaling, suggesting a possible role as a chemo-sensitizer rather than a standalone cytotoxic agent.

Fenbendazole and Mebendazole

• Microtubule/tubulin disruption: As benzimidazole anthelmintics, both drugs bind β-tubulin in parasites; the same mechanism has been proposed to disrupt cancer cell division, analogous to (but pharmacologically distinct from) established microtubule-targeting chemotherapy agents.
• Activity in chemo-resistant cell lines: Park et al. (2022), published in the Korean Journal of Physiology & Pharmacology, found that fenbendazole induced apoptosis and G2/M cell-cycle arrest in 5-fluorouracil-resistant colorectal cancer cells (SNU-C5/5-FUR) in vitro, and that this activity did not require functional p53 — a gene frequently mutated in treatment-resistant CRC.
• TNIK/Wnt degradation (mebendazole): Mechanistic work has proposed that mebendazole promotes degradation of TNIK, a kinase that supports Wnt/β-catenin signaling in colorectal cancer cells.

Important context: laboratory concentrations used in these studies often exceed what can be safely achieved in human blood at approved or even substantially escalated oral doses. A mechanism demonstrated in a petri dish does not automatically mean the same effect occurs in a person taking the drug by mouth — this is precisely the translational gap that clinical trials exist to test.

3. Evidence Hierarchy: What Kind of Proof Is This?

Not all "evidence" carries the same weight. Using the CEBM (Centre for Evidence-Based Medicine) hierarchy, here is where each category of information referenced on this topic actually falls:

CEBM Level	What It Means	Where It Applies Here
Level 1–2	Randomized controlled trials, systematic reviews of RCTs	One small placebo-controlled RCT of mebendazole (Hegazy et al., 2022, n=40). No RCT exists for ivermectin or fenbendazole in CRC.
Level 3	Cohort / case-control studies	None identified specific to CRC as of this update.
Level 4	Peer-reviewed, individually verified case reports/series	A small number of published case reports (e.g., Aydin et al., 2024, involving mebendazole plus dual immunotherapy), including at least one published adverse-event case report (Yamaguchi et al., 2021).
Level 5	Expert opinion, mechanistic reasoning, in vitro/animal studies	Zhou 2021, Park 2022, Loftalizadeh 2022, Jiang 2019 — laboratory studies only.
Not clinical evidence	Self-reported, non-peer-reviewed anecdotes	The hundreds of social media "testimonials" circulating under this topic. These are not independently verified, are frequently confounded by concurrent chemotherapy or surgery, and cannot rule out survivorship bias (failures are rarely posted). See Section 5.

4. The Actual Human Clinical Trial Data

Mebendazole + Bevacizumab + FOLFOX4 (Hegazy et al., 2022)

This is the single most rigorous piece of human evidence on this topic, and it deserves to be reported accurately rather than folded into a pile of anecdotes. It was a prospective, randomized, double-blind, placebo-controlled trial enrolling 40 patients with metastatic colorectal cancer, published in Life Sciences (2022). All patients received six cycles of bevacizumab plus FOLFOX4; 20 additionally received mebendazole 500 mg orally twice daily for 12 weeks, and 20 received a matching placebo.

Outcome (12 weeks)	Placebo Group	Mebendazole Group
Overall response rate	10%	65%
Median progression-free survival	3 months	9.25 months
Tolerability	—	Well tolerated in this cohort

These are striking numbers for a 40-patient trial, and they are a genuine reason for scientific optimism about mebendazole specifically, as an adjunct to standard chemotherapy — not a replacement for it. At the same time, honest evidence reporting requires flagging the limitations: this was a single-center study with a small sample size, and results of this magnitude have not yet been independently replicated in a larger, multi-center trial. That replication is exactly what would be needed before this could influence treatment guidelines.

Case Report: Mebendazole With Dual Immunotherapy (Aydin et al., 2024)

Published in Frontiers in Oncology, this case report described a heavily pretreated metastatic colorectal cancer patient who achieved a molecular complete response on a regimen combining nivolumab, ipilimumab, lenvatinib, and mebendazole (100 mg twice daily). As a single case report, it is hypothesis-generating rather than proof of effect, but it is a legitimately peer-reviewed data point — a different category from an unverified social media post.

Trials Currently Underway

Per ASCO's May 2026 Clinical Notice, human trial activity on ivermectin in oncology is real but still early: a phase I/II trial is evaluating ivermectin combined with balstilimab or pembrolizumab in metastatic triple-negative breast cancer, with preliminary data on the first nine patients presented at the 2025 ASCO Annual Meeting. A separate randomized phase II trial (ICONIC), pairing different ivermectin doses with immune checkpoint inhibitors across 80 patients with solid tumors, was expected to begin enrollment in July 2026. Neither trial is specific to colorectal cancer, and results are not expected before late 2027.

Separately, a 2026 ASCO Gastrointestinal Cancers Symposium abstract (Phan et al.) reported a single-institution chart review of patterns of ivermectin and fenbendazole use among gastrointestinal cancer patients — evidence that academic oncology centers are now formally studying how and why patients are using these drugs outside of trials, even without endorsing the practice.

5. The Social Media Case-Report Phenomenon

Any honest treatment of this topic has to address where most of the public "evidence" for ivermectin/fenbendazole in colorectal cancer actually comes from: a large volume of first-person and second-hand testimonials shared on X (formerly Twitter) and Substack, describing dramatic tumor marker drops and remissions after starting these drugs, frequently alongside standard chemotherapy. A large share of these posts have circulated under the name of Dr. William Makis, a Canadian radiologist whose accounts have been widely shared and republished, including on integrative-oncology sites.

Readers deserve accurate context on the source of these accounts. As of this update, Mr. Makis's medical license is inactive, and in March 2026 the College of Physicians & Surgeons of Alberta obtained a permanent injunction from the Alberta Court of King's Bench restricting him from representing himself as licensed to practice medicine, from offering health services or cancer treatment advice to the public, and from using the title "doctor" or "oncologist" in connection with providing a health service. This is a matter of public record, not a judgment this article is making independently, and it is directly relevant to how much evidentiary weight the associated posts can bear.

Separately from the question of who is posting them, self-reported online testimonials have structural problems that make them unusable as clinical evidence regardless of source:

• No denominator. There is no way to know how many patients tried these drugs and did not respond, progressed, or were harmed — only successes tend to be shared.
• Confounding by concurrent standard treatment. The large majority of the circulating reports involve patients simultaneously receiving chemotherapy, radiation, or recent surgery, making it impossible to attribute tumor response to the repurposed drug versus the guideline-based treatment they were also receiving.
• No independent verification. Imaging and lab values are typically relayed as screenshots or paraphrased quotes rather than verified through a chart review or peer review process.
• Commercial incentive. Several of these accounts are directly tied to the sale of compounded drug products, supplements, or paid consultations, which is a recognized conflict of interest in evaluating any treatment claim.

None of this means the underlying pharmacological hypothesis is false — Section 2 and Section 4 show it is worth taking seriously as a research question. It means that a testimonial is not a substitute for a trial, and a large number of testimonials is not the same thing as strong evidence — it is a large number of anecdotes.

6. ASCO's May 2026 Clinical Notice

In May 2026, the American Society of Clinical Oncology (ASCO) — the largest professional organization of oncologists in the United States — published a formal Clinical Notice addressing this exact topic. Its core conclusions:

• There is no robust, peer-reviewed clinical evidence that ivermectin or fenbendazole is safe or effective for treating any human malignancy.
• ASCO "strongly cautions" that neither drug should be used to treat cancer, or as an adjunct to established cancer therapies, outside the regulatory safeguards of a well-designed clinical trial.
• The current lack of established clinical benefit, combined with the potential for toxicity and harmful drug interactions, represents "an unacceptable risk to patients."
• Fenbendazole is not FDA-approved for use in humans under any indication; ivermectin is FDA-approved only for specific parasitic infections, at doses far below what is being described in online cancer protocols.
• ASCO explicitly frames the viral spread of these regimens on social media as a patient-safety issue, and urges oncologists to proactively ask patients about outside supplement and drug use rather than wait for voluntary disclosure.

This is the mainstream clinical consensus as it currently stands, and it should be presented alongside — not instead of — the preclinical rationale discussed above. Readers are entitled to both pieces of the picture.

7. Safety Considerations Patients Overlook

This Is Not Theoretical: A Published Liver Injury Case

Yamaguchi et al. (2021), published in Case Reports in Oncology, documented drug-induced liver injury in a lung cancer patient following self-administration of fenbendazole based on information obtained from social media. This is exactly the scenario this article is trying to help readers avoid: an unsupervised dosing decision, made without baseline or follow-up liver monitoring, based on a viral post rather than a treating physician's guidance.

Veterinary Formulations Are Not Human Formulations

Fenbendazole is manufactured and regulated as an animal dewormer (marketed for dogs, livestock, and other animals under names including Panacur and Safe-Guard). Products formulated for goats, cattle, or dogs are not manufactured, tested, or dosed to human pharmaceutical standards, and their purity, concentration, and excipients are not controlled for human oral consumption. Sourcing an unapproved human cancer treatment from an animal-medicine supply chain compounds an already unproven intervention with an additional, avoidable layer of risk.

Drug Interactions With Standard Chemotherapy

Both ivermectin and the benzimidazoles are metabolized through hepatic cytochrome P450 pathways that overlap with several chemotherapy agents used in CRC regimens (including irinotecan and oxaliplatin-based protocols). Concurrent use has the potential to alter drug clearance in ways that are not yet well characterized in humans — another reason ASCO specifically flags "harmful drug interactions" as a named risk, not a hypothetical one.

Never Conceal Supplement or Drug Use From Your Oncology Team

Some patient accounts describing these regimens explicitly mention not disclosing use to their treating oncologist. This is worth addressing directly: concealing any medication or supplement from the clinicians managing your chemotherapy removes their ability to monitor for interactions, adjust chemotherapy dosing appropriately, or correctly interpret your labs and scans. Whatever a patient ultimately decides about a repurposed drug, full disclosure to the treatment team is a safety requirement, not an optional courtesy — and it works in the patient's favor, not against it.

8. Evidence-Based Adjuncts Worth Discussing With Your Oncologist

For patients looking for evidence-supported ways to complement standard CRC treatment, several better-validated strategies are worth raising with an oncology team — none of these replace guideline therapy, but they carry considerably stronger human evidence than the repurposed antiparasitics discussed above:

• Vitamin D status: A 2025 pooled analysis in Nutrients, covering over 1.3 million participants across 50 studies, found consistent associations between low vitamin D status and higher colorectal cancer risk, and better outcomes at adequate levels. Correcting a documented deficiency is a low-risk, evidence-supported conversation to have with your physician.
• Cruciferous vegetables: A 2025 BMC Gastroenterology meta-analysis of 17 studies (639,539 participants) found a 17% lower odds of colon cancer among higher cruciferous vegetable intake, with benefit plateauing around 40–60g daily (roughly half a cup of cooked broccoli).
• Berberine for adenoma recurrence: A 6-year follow-up of a randomized controlled trial in Cell Reports Medicine (2025) found sustained reductions in adenoma recurrence (34.7% vs. 52.1%) and neoplasm occurrence (63.4% vs. 71.0%) after berberine treatment following polypectomy.
• Exercise: Emerging trial data (New England Journal of Medicine, 2025) has shown structured exercise programs improving disease-free survival after colon cancer treatment — a genuinely practice-changing, low-risk finding.
• Low-dose aspirin: A 2025 NEJM trial found benefit specifically in PI3K-altered, localized colorectal cancer — a good example of precision-guided repurposing that reached trial-level evidence rather than remaining anecdotal.

Every item on this list should still be discussed with your treating oncologist before starting, given individual contraindications (e.g., bleeding risk with aspirin, interactions with anticoagulants).

9. If You're Considering This: A Practical Framework

Step	Why It Matters
Tell your oncologist you're considering it — before you start	Allows baseline liver/kidney monitoring and a real review of interactions with your specific chemotherapy regimen
Ask about clinical trial enrollment	The ICONIC trial and the ivermectin/immunotherapy TNBC trial represent a path to receiving these agents within a monitored, regulated setting
Never substitute for guideline chemotherapy, surgery, or radiation	No trial has tested these agents as monotherapy replacements for standard CRC treatment; the one positive RCT used mebendazole strictly as an add-on to full-dose chemotherapy
Never source from veterinary/animal-medicine channels	Animal formulations are not manufactured or dosed to human pharmaceutical standards
Request liver function monitoring if you and your physician proceed	At least one published case of drug-induced liver injury exists from unsupervised use

10. Frequently Asked Questions

Does ivermectin cure colorectal cancer?
No. There is no clinical trial evidence that ivermectin cures colorectal cancer in humans. Laboratory studies show it can inhibit colorectal cancer cell growth and interfere with Wnt signaling in vitro, but this has not been demonstrated in human trials.

Is fenbendazole approved for human use?
No. Fenbendazole is approved only as a veterinary anthelmintic. It is not FDA-approved for any human indication, including cancer.

What does ASCO say about ivermectin and fenbendazole for cancer?
In a May 2026 Clinical Notice, ASCO stated there is no robust, peer-reviewed clinical evidence that either drug is safe or effective for treating any human malignancy, and strongly cautioned against their use outside of a registered clinical trial, citing risks of toxicity and drug interaction.

Is the mebendazole colorectal cancer trial real?
Yes. Hegazy et al. (2022) published a randomized, double-blind, placebo-controlled trial of 40 metastatic colorectal cancer patients in the journal Life Sciences, finding that adding mebendazole to bevacizumab/FOLFOX4 chemotherapy improved response rate and progression-free survival compared to chemotherapy alone. The sample size was small and has not yet been replicated in a larger trial.

Are the ivermectin/fenbendazole cancer "case reports" on social media reliable?
They should be treated as unverified patient anecdotes, not clinical data. They typically involve concurrent standard treatment (making attribution impossible), lack independent verification, and a substantial share circulate under sources without an active medical license.

Can I take fenbendazole or ivermectin alongside my chemotherapy?
This is a decision to make with your treating oncologist, not independently. These drugs can interact with chemotherapy metabolism, and any use should be disclosed and monitored rather than concealed.

11. Conclusion

The honest version of this story is less viral than the version circulating on social media, but it is more useful to an actual cancer patient making decisions under pressure. The pharmacological rationale for repurposing ivermectin and the benzimidazoles in colorectal cancer is real and scientifically interesting. The human clinical evidence, at this point, consists of one small but genuinely positive randomized trial of mebendazole as a chemotherapy adjunct, a handful of peer-reviewed case reports, and early-phase immunotherapy combination trials that have not yet reported results. It does not yet include proof that these drugs treat colorectal cancer on their own, and the field's own professional body has said so directly. Patients deserve to hear about the legitimate research question — and to hear, with equal clarity, that the current evidence does not support replacing standard treatment, that unsupervised self-dosing carries documented risk, and that full transparency with an oncology team is a safety requirement, not a liability.

Medical Disclaimer

This article is for educational purposes only and is not medical advice. It is not a treatment protocol and should not be used as one. Fenbendazole is not approved for human use under any indication. Ivermectin is FDA-approved only for specific parasitic infections, at doses far below those discussed in online cancer regimens. Neither drug should be used to treat cancer, or alongside cancer treatment, outside of a clinical trial or without your treating oncologist's direct knowledge and supervision.

If you or a loved one is facing a colorectal cancer diagnosis, please discuss all treatment options — including clinical trial enrollment — with a licensed oncologist. Do not start, stop, or combine any medication or supplement without medical supervision.

This article is part of the Colorectal Cancer series.

References

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