Mebendazole and Ivermectin in Integrative Oncology: A Rigorous Evidence-Based Evaluation of Repurposed Antiparasitic Agents in Cancer Care

Yoon Hang Kim, MD, MPH

Board-Certified in Preventive Medicine | Integrative & Functional Medicine Physician

July 2026

Introduction: The Promise of Drug Repurposing

Drug repurposing — the identification of new therapeutic applications for existing, approved medications — has become one of the most actively discussed strategies in oncology. The appeal is straightforward: agents with decades of established safety data, well-characterized pharmacokinetics, and global availability could theoretically bypass years of early-phase development and reach clients faster and more affordably than novel therapeutics.

Two antiparasitic agents, mebendazole and ivermectin, have emerged at the center of this conversation. Preclinical research spanning more than a decade has demonstrated intriguing anticancer properties for both drugs across multiple tumor models. Social media amplification, celebrity endorsements, and patient advocacy networks have accelerated public interest far beyond what the current clinical evidence supports. In June 2026, the American Society of Clinical Oncology (ASCO) issued a formal Clinical Notice cautioning against the use of ivermectin and related agents for cancer treatment outside of clinical trials — a rare step reflecting the urgency of the situation.

This article provides a rigorous, transparent evaluation of where the science actually stands as of mid-2026. The goal is neither to champion these agents prematurely nor to dismiss legitimate scientific inquiry, but to help clinicians and informed clients distinguish between biological plausibility, preclinical promise, and proven clinical benefit — three very different categories of evidence.

Mebendazole: From Anthelmintic to Anticancer Candidate

Pharmacology and Preclinical Rationale

Mebendazole (MBZ) is a synthetic benzimidazole introduced for human use in 1971 for the treatment of intestinal helminth infections. Its primary mechanism — inhibition of tubulin polymerization and disruption of microtubule dynamics — is mechanistically analogous to the vinca alkaloids (vincristine, vinblastine), an established class of cytotoxic chemotherapy agents. This overlap was the original impetus for investigating MBZ in cancer.

Beyond tubulin inhibition, preclinical studies have identified several additional anticancer mechanisms. MBZ has been shown to function as a multityrosine kinase inhibitor targeting VEGFR2 (anti-angiogenic), BRAF, and ERK signaling. It has demonstrated pro-apoptotic effects through caspase activation, hedgehog pathway inhibition, and immunomodulatory activity — including macrophage polarization from the tumor-promoting M2 phenotype toward the tumor-inhibitory M1 phenotype. Its ability to cross the blood-brain barrier makes it particularly relevant for CNS malignancies.

In vitro and animal model studies have demonstrated activity against glioblastoma, colorectal cancer, breast cancer, lung cancer, adrenocortical carcinoma, pancreatic cancer, medulloblastoma, and melanoma. In the seminal 2011 study by Bai and colleagues at Johns Hopkins (which began as a serendipitous observation that the related benzimidazole fenbendazole inhibited tumor engraftment), MBZ significantly extended mean survival by up to 63% in syngeneic and xenograft orthotopic mouse glioma models. A 2024 Stanford-led preclinical study (Rodrigues et al.) further characterized MBZ's activity profile.

Clinical Trial Evidence: What We Actually Know

Johns Hopkins Phase I (Gallia et al., 2021): This single-center dose-escalation study enrolled 24 patients with newly diagnosed high-grade gliomas (18 glioblastoma, 6 anaplastic glioma) who received MBZ in combination with adjuvant temozolomide. Dose-escalation levels ranged from 25 to 200 mg/kg/day. Fifteen patients were enrolled at the highest dose. Four patients at 200 mg/kg developed grade 3 hepatotransaminase elevations, which reversed upon dose modification or discontinuation. Mean overall survival from diagnosis for all 24 patients was 21.0 months (95% CI: 14.3–31.2) with 41.7% alive at 2 years — a figure that compares favorably to historical benchmarks but was not derived from a controlled comparison. The investigators concluded that MBZ demonstrated "long-term safety and acceptable toxicity" and warranted further efficacy investigation. Critically, however, this was a safety study without a control arm — the survival data cannot be attributed to MBZ.

Tata Memorial Phase II (Patil et al., 2022): This randomized, open-label study enrolled 88 patients with recurrent glioblastoma across two arms: MBZ plus temozolomide versus MBZ plus lomustine. The 9-month overall survival was 36.6% (TMZ-MBZ arm) and 45% (CCNU-MBZ arm). Neither arm met the pre-specified threshold of 55% OS at 9 months that would have warranted further evaluation. Grade 3–5 adverse events occurred in 18.6% and 9.5%, respectively. There were no treatment-related deaths.

Uppsala Phase 2a (Mansoori et al., 2021): This is the study that demands sober attention. Eleven patients with treatment-refractory gastrointestinal cancer received individualized-dose MBZ monotherapy (up to 4 g/day targeting serum concentrations of 300 ng/mL). All patients who were radiologically evaluated showed progressive disease at 8 weeks. Four of eight evaluable patients (40%) met established criteria for hyperprogression. Only 5 of 10 patients achieved target serum concentrations, highlighting MBZ's notoriously variable and often poor oral bioavailability. While MBZ was well tolerated from a safety standpoint, it showed no anticancer efficacy as monotherapy in this population — and the hyperprogression signal demands further investigation.

Egyptian mCRC Randomized Controlled Trial (2022): This is arguably the most methodologically rigorous MBZ cancer trial published to date (Hegazy et al., Life Sciences, 2022). A prospective, randomized, double-blind, placebo-controlled study enrolled 40 patients with metastatic colorectal cancer. Patients received either bevacizumab with FOLFOX4 plus MBZ 500 mg twice daily, or bevacizumab with FOLFOX4 plus placebo, for 12 weeks. The MBZ arm reported a markedly higher overall response rate at 12 weeks (65% vs. 10%; p<0.001), longer median progression-free survival (9.25 vs. 3 months; p<0.001), and a significant decline in serum VEGF (p=0.006). These are striking effect sizes. However, several caveats temper enthusiasm: the difference in one-year overall survival between groups did not reach statistical significance, the trial was single-center and small (n=40), the very large response-rate gap is unusual for an adjunctive agent and warrants scrutiny, and the results have not yet been independently replicated in a larger, multicenter setting. A positive signal, not a practice-changing result.

Pediatric Phase I Studies: MBZ has been investigated in combination with bevacizumab and irinotecan in pediatric high-grade gliomas (Krystal et al., 2024), demonstrating safety and tolerability at doses up to 200 mg/kg/day. A separate pediatric Phase I trial (NCT02644291) at Johns Hopkins for recurrent pediatric brain tumors has been completed, though detailed results have not yet been published.

The Bioavailability Problem

A critical and often underappreciated limitation of MBZ in oncology is its poor and highly variable oral bioavailability. MBZ undergoes extensive first-pass hepatic metabolism, and systemic absorption is heavily influenced by the polymorph used (polymorph C is preferred for systemic conditions), fat content of meals, and individual variation. In the Uppsala study, only half of patients achieved target serum concentrations despite doses up to 4 g/day. This pharmacokinetic challenge may explain the disconnect between promising in vitro data and the inconsistent clinical results observed to date.

Ivermectin: Extensive Preclinical Portfolio, Minimal Clinical Validation

Preclinical Mechanisms

Ivermectin (IVM) is a macrocyclic lactone derived from avermectin, approved for human use in the treatment of strongyloidiasis and onchocerciasis, and topically for head lice and rosacea. Its discoverers (Satoshi Ōmura and William Campbell) received the 2015 Nobel Prize in Physiology or Medicine for its contributions to global health.

Preclinical studies have described an impressive breadth of anticancer mechanisms. IVM has been shown to modulate Wnt/β-catenin, PI3K/Akt/mTOR, STAT3, and NF-κB signaling pathways. It induces apoptosis through mitochondrial dysfunction and reactive oxygen species generation. It inhibits cancer cell proliferation, metastasis, and angiogenesis via PAK1 kinase inhibition. Preclinical studies suggest it may convert immunologically "cold" tumors to "hot" tumors by enhancing T-cell infiltration — a mechanism of particular theoretical interest in the immunotherapy era.

A 2025 review catalogued over 14 distinct anticancer mechanisms across more than 12 tumor types, including colorectal, breast, lung, melanoma, glioma, leukemia, pancreatic, and ovarian cancer models.

The Concentration Problem: The Central Challenge

This is the single most important issue in evaluating ivermectin's oncologic potential, and it is frequently glossed over in advocacy literature.

The effective concentrations required for anticancer activity in cell culture studies are typically in the low micromolar range (roughly 2–10 μM, and higher in some studies). At standard FDA-approved doses for parasitic infections, peak plasma concentrations in humans are approximately 50 nM (about 46.6 ng/mL) — roughly 50- to 100-fold lower than the concentrations that produce anticancer effects in vitro. Because ivermectin is also highly protein-bound (approximately 93%), the free (unbound) concentration available to act on cells is lower still. Even at the highest doses studied in pharmacokinetic trials, peak plasma concentrations only reach approximately 300 nM — still well below most reported in vitro effective concentrations.

A 2023 study (published in PNAS) demonstrated that ivermectin's in vitro antiviral activity (initially reported for SARS-CoV-2) was attributable to nonspecific membrane bilayer perturbation at the same concentrations that produced cytotoxicity — raising serious concerns that some reported "anticancer" effects may simply reflect generalized cellular toxicity at supraphysiologic concentrations rather than selective antitumor activity.

Whether tissue-level accumulation in tumors (IVM is highly lipophilic), sustained low-dose exposure, or novel formulations could bridge this pharmacokinetic gap remains an open and urgent research question.

Clinical Evidence

Cedars-Sinai Phase I/II (Yuan et al., ASCO 2025): This is currently the most rigorously designed ongoing clinical trial of IVM in cancer. Investigators at Cedars-Sinai Medical Center are evaluating IVM in combination with balstilimab (anti-PD-1) in patients with metastatic triple-negative breast cancer (TNBC) who have progressed on 1–2 prior lines of therapy (NCT05318469). Preliminary results from the first 9 patients were presented at the 2025 ASCO Annual Meeting. The combination was safe and well tolerated, with no treatment-related serious adverse events. Median PFS was 2.5 months. The 4-month clinical benefit rate was 37.5%. While the investigators described the CBR as "encouraging" in this heavily pretreated population, overall survival data are premature and no comparator arm exists at this stage.

ICONIC Trial (NCT07487805): A Phase II randomized trial, with an estimated start date of July 2026, plans to enroll 80 patients with advanced solid tumors to evaluate different doses of IVM combined with immune checkpoint inhibitors. Results are anticipated in late 2027. This study is notable for its rigorous design, including randomization and dose-response assessment — precisely the type of trial needed to advance or refute IVM's oncologic potential.

Annals of Oncology Review (ASCO 2025 poster): A review presented at ASCO 2025 (published in Annals of Oncology) evaluated the available literature on IVM in cancer. Investigators identified 269 PubMed search results between 2000 and 2025 involving ivermectin and cancer; of these, 50 were preclinical studies, and — by their PubMed methodology at that time — none were completed clinical studies involving humans. The only active clinical trial identified was the Cedars-Sinai TNBC study. The majority of 32 identified news stories cautioned the public on the lack of clinical data. (Note: this count predates the wider circulation of the Cedars-Sinai preliminary abstract and the 2026 Hulscher observational report discussed below; neither changes the underlying conclusion that no adequately controlled human efficacy data exist.)

The Hulscher et al. Study: A Case Study in Evidence Interpretation

The June 2026 publication by Hulscher et al. in Anticancer Research has become a flashpoint in this debate and warrants detailed critical analysis. The study analyzed a prospective observational cohort of 197 cancer patients prescribed compounded capsules containing 25 mg ivermectin and 250 mg mebendazole through a U.S. telemedicine platform (The Wellness Company). Of 197 enrolled, 122 (61.9%) completed 6-month follow-up.

The headline finding — that 84.4% of patients reported "clinical benefit" (defined as cancer disappearance, tumor regression, or cancer stabilization) — has been widely promoted in social media and advocacy circles. However, several critical methodological limitations demand acknowledgment.

Critical Methodological Concerns

Self-reported outcomes: All cancer status assessments were patient-reported via digital surveys — not verified by imaging (CT, PET, MRI), pathology, or physician assessment. Self-reported cancer status is inherently unreliable and subject to multiple biases including optimism bias, confirmation bias, recall bias, and social desirability bias.

No control group: Without a comparator arm, it is impossible to determine whether reported outcomes reflect the effects of IVM/MBZ, concurrent standard oncology therapies (the study population was not restricted from receiving conventional treatment), natural disease course, regression to the mean, or placebo effect.

Attrition bias: 38.1% of participants were lost to follow-up. Patients who are doing poorly or who have died are systematically less likely to complete surveys — a well-recognized source of survivorship bias that inflates favorable outcomes.

Heterogeneous population: The cohort included diverse cancer types, stages, and concurrent treatments, making it impossible to isolate IVM/MBZ effects.

Conflicts of interest: The study was conducted through The Wellness Company, a telemedicine platform that commercially sells ivermectin and mebendazole products. Several study authors are affiliated with the McCullough Foundation and have financial relationships with the commercial entity prescribing these agents. This does not automatically invalidate the findings, but it is a significant conflict that readers should weigh.

Expression of Concern: The journal Anticancer Research issued a formal Expression of Concern shortly after publication, stating that "serious scientific concerns were raised by the international medical community regarding the verifiability and statistical reliability, and ethical oversight of the underlying dataset." The editorial board noted that a study reporting a "Clinical Benefit Ratio of 84.4%" must rest on "a verifiably real clinical foundation and adhere to established ethical frameworks for human subject research."

This study is best characterized as hypothesis-generating — a descriptor the authors themselves use. It provides signal, not proof. It would be inappropriate to cite it as evidence that IVM and MBZ are effective cancer treatments.

Evidence Summary Table

Table 1. Summary of key clinical studies evaluating mebendazole and/or ivermectin in cancer (as of July 2026).

Professional Society Position: ASCO Clinical Notice (June 2026)

In May/June 2026, the American Society of Clinical Oncology (ASCO) published a formal Clinical Notice explicitly recommending against the use of ivermectin and fenbendazole for cancer treatment outside of clinical trials. Key statements include:

"There is no robust, peer-reviewed clinical evidence demonstrating that either ivermectin or fenbendazole is safe or effective for treating any human malignancy."

ASCO noted that replicating drug concentrations used in laboratory settings would require human doses far exceeding established safety limits. The society recommended that oncologists routinely ask patients about supplement and alternative therapy use; approach conversations with respectful curiosity; and educate with empathy while communicating potential risks.

It is worth noting that the National Cancer Institute (NCI) has also initiated preclinical evaluation of ivermectin's anticancer potential as of April 2026 — an indication that the scientific establishment considers the hypothesis worthy of formal investigation through appropriate channels.

Safety Considerations and Clinical Risks

Mebendazole

MBZ has a favorable safety profile when used short-term for antiparasitic indications. With prolonged, high-dose use in oncology investigations, the primary concerns include reversible hepatotoxicity (grade 3 ALT/AST elevations observed in the Johns Hopkins Phase I study), myelosuppression (bone marrow suppression), and gastrointestinal symptoms (nausea, abdominal pain, decreased appetite). Baseline and periodic monitoring of hepatic function (ALT, AST, alkaline phosphatase, bilirubin) and complete blood counts is advisable for any client using MBZ at cancer-relevant doses. The hyperprogression signal observed in the Uppsala GI cancer study, while potentially related to natural disease course in a refractory population, warrants continued vigilance.

Ivermectin

At standard antiparasitic doses (150–200 μg/kg), ivermectin has an excellent safety profile. However, the doses advocated in some cancer protocols (including the Makis protocols, which Dr. Paul Marik has since publicly cautioned against as "potentially toxic") are substantially higher and carry risk of neurologic toxicity (ataxia, seizures, altered consciousness), hypotension, and hepatotoxicity. Drug interactions are a significant concern — IVM is a CYP3A4 substrate, and concomitant use with CYP3A4 inhibitors can dramatically increase plasma levels. A case report described severe neurotoxicity in a patient with metastatic osteosarcoma receiving regorafenib concurrently with IVM, likely due to a pharmacokinetic interaction. The ICONIC trial specifically aims to evaluate whether IVM may impact gut microbiome composition — a key modulator of immune checkpoint inhibitor efficacy — with unknown consequences.

Risk of Treatment Delay

Perhaps the greatest safety concern is indirect: clients who pursue unproven antiparasitic regimens may delay or forgo evidence-based treatments with demonstrated survival benefit. In cancer, where treatment windows can be measured in weeks, this opportunity cost may be life-altering.

A Balanced Assessment: Where Do We Actually Stand?

What the evidence supports:

Both mebendazole and ivermectin have robust preclinical anticancer activity across multiple mechanisms and tumor types. MBZ has demonstrated safety in early-phase clinical trials at cancer-relevant doses. The one small RCT in metastatic colorectal cancer (MBZ) showed a positive signal. The Cedars-Sinai IVM/immunotherapy trial suggests the combination is tolerable and warrants further study. The biological rationale for investigation is legitimate, and this area of inquiry deserves — and is receiving — rigorous clinical investigation.

What the evidence does not support:

There is currently no robust clinical evidence from adequately powered, well-controlled trials demonstrating that either mebendazole or ivermectin — alone or in combination — produces meaningful antitumor responses or survival benefit in any human cancer. The pharmacokinetic gap between effective in vitro concentrations and achievable human plasma levels remains a fundamental translational challenge, particularly for ivermectin. Self-reported observational data from cohorts with significant commercial conflicts of interest do not constitute proof of efficacy. The 84.4% "clinical benefit" figure from the Hulscher study is not a validated oncologic endpoint.

What needs to happen:

Properly designed, adequately powered randomized controlled trials — with objective endpoints including imaging-confirmed response rates, progression-free survival, and overall survival — are essential. The ICONIC trial (NCT07487805) represents exactly this type of rigorous evaluation. Until such trials report results, the use of these agents outside of clinical trials carries unquantified risk and unproven benefit.

Guidance for Clients and Clinicians

For clients who are interested in or currently using these agents, the following principles apply:

First, do not delay or replace proven cancer therapies. Mebendazole and ivermectin are not substitutes for surgery, chemotherapy, immunotherapy, radiation, or any other evidence-based treatment recommended by your oncology team.

Second, maintain transparent communication with all members of your healthcare team. Drug interactions (particularly with CYP3A4-metabolized agents) can be clinically significant. Your oncologist needs to know about all supplements and medications you are taking.

Third, seek objective monitoring. If you choose to use these agents adjunctively, insist on objective outcome tracking — imaging studies, tumor markers, and laboratory monitoring — rather than relying on subjective symptom assessment alone.

Fourth, consider clinical trial enrollment. If you are interested in repurposed antiparasitic agents, the most rigorous and safest path is participation in a formal clinical trial where dosing, monitoring, and outcomes are systematically managed.

Fifth, exercise extreme caution with unregulated sources. Veterinary formulations, compounded products without quality assurance, and dosing protocols promoted by non-medical influencers carry real risk of harm.

Conclusion

Mebendazole and ivermectin represent legitimate areas of oncologic inquiry with strong preclinical rationale. The scientific question is not whether these agents have anticancer biological activity — they clearly do, at least in vitro and in animal models. The operative questions are whether that activity translates to clinically meaningful benefit in humans at safe and achievable doses, and whether that benefit outweighs the risks.

As of mid-2026, those questions remain unanswered. The preclinical data are compelling. The clinical data are early, fragmentary, and mixed. The most methodologically rigorous study to date (the Egyptian mCRC RCT) provides a positive signal for MBZ as an adjunct to standard chemotherapy, but with n=40 at a single center, it is far from definitive. For ivermectin, the clinical evidence base in cancer is vanishingly thin — essentially preliminary safety data from 9 patients and a deeply flawed observational study that has already triggered a journal expression of concern.

The path forward is clinical trials — not social media testimonials, not uncontrolled observational cohorts, and not premature clinical adoption. Responsible integrative oncology means maintaining intellectual honesty about the limits of current evidence while supporting rigorous investigation of promising hypotheses. The truth is: we simply do not yet know whether these agents help, harm, or are inert in the complex biology of human cancer. The only responsible way to find out is through the scientific process.

Selected References

1. Gallia GL, Holdhoff M, Brem H, et al. Mebendazole and temozolomide in patients with newly diagnosed high-grade gliomas: Results of a phase 1 clinical trial. Neurooncol Adv. 2021;3(1):vdaa154.

2. Patil VM, Menon N, Chatterjee A, et al. Mebendazole plus lomustine or temozolomide in patients with recurrent glioblastoma: A randomised open-label phase II trial. EClinicalMedicine. 2022;49:101449.

3. Mansoori S, Fryknäs M, Alvfors C, et al. A phase 2a clinical study on the safety and efficacy of individualized dosed mebendazole in patients with advanced gastrointestinal cancer. Sci Rep. 2021;11:8981.

4. Hulscher N, Victory K, Thorp JA, et al. Real-world Clinical Outcomes of Ivermectin and Mebendazole in Cancer Patients: Results from a Prospective Observational Cohort. Anticancer Res. 2026;46(6):3243-3255. [Expression of Concern issued]

5. Bitar JS, Walker M, Lin D, et al. (Yuan Y, senior author/PI). A phase I/II study evaluating the safety and efficacy of ivermectin in combination with balstilimab in patients with metastatic triple negative breast cancer. J Clin Oncol. 2025;43(16_suppl):e13146. [2025 ASCO Annual Meeting abstract; NCT05318469]

6. Anticancer Research Editorial Board. Expression of Concern regarding Hulscher et al. Anticancer Res. 2026;46(6):e3243.

7. American Society of Clinical Oncology (ASCO). Clinical Notice: Recommending Against Ivermectin and Fenbendazole for Cancer Treatment, Outside of Clinical Trials. May 2026.

8. ClinicalTrials.gov. Ivermectin Combined With Immune Checkpoint Inhibition in Cancer (ICONIC). NCT07487805.

9. Annals of Oncology. 2833P Ivermectin in cancer, 2025: Internet trends, scientific data, ongoing trials, and news coverage. ASCO 2025.

10. Pantziarka P, Bouche G, Meheus L, Sukhatme V, Sukhatme VP. Repurposing Drugs in Oncology (ReDO) — mebendazole as an anti-cancer agent. Ecancermedicalscience. 2014;8:443.

11. Krystal J, Hanson D, Donnelly D, Atlas M. A phase 1 study of mebendazole with bevacizumab and irinotecan in high-grade gliomas. Pediatr Blood Cancer. 2024;71(4):e30874.

12. Schmith VD, Zhou JJ, Lohmer LRL. The approved dose of ivermectin alone is not the ideal dose for the treatment of COVID-19. Clin Pharmacol Ther. 2020;108(4):762-765.

13. Hegazy SK, El-Azab GA, Zakaria F, Mostafa MF, El-Ghoneimy RA. Mebendazole; from an anti-parasitic drug to a promising candidate for drug repurposing in colorectal cancer. Life Sci. 2022;299:120536.

14. Bai RY, Staedtke V, Aprhys CM, Gallia GL, Riggins GJ. Antiparasitic mebendazole shows survival benefit in 2 preclinical models of glioblastoma multiforme. Neuro Oncol. 2011;13(9):974-982.

15. Gilene S, et al. The Threat of Medical Misinformation: A Case of Ivermectin Toxicity in a Pediatric Oncology Patient. Pediatr Blood Cancer. 2025.

16. American Cancer Society. What to Know About Ivermectin. 2026; What to Know About Fenbendazole. 2025.

About Dr. Kim

Dr. Yoon Hang "John" Kim is a board-certified Preventive Medicine physician with over 20 years of experience in integrative and functional medicine. A graduate of the University of Arizona's Integrative Medicine Fellowship (Osher Fellow) under Dr. Andrew Weil, Dr. Kim holds additional certifications in medical acupuncture (UCLA) and integrative holistic medicine. He specializes in low dose naltrexone (LDN), autoimmune conditions, chronic pain syndromes, integrative oncology, fibromyalgia, chronic fatigue syndrome, mast cell activation syndrome (MCAS), and mold-related illness. He is the author of three books and more than 20 peer-reviewed and professional articles, and is the founder of the LDN Support Group.

Professional: www.yoonhangkim.com  |  Clinical: www.directintegrativecare.com