Ivermectin, Fenbendazole, and Mebendazole in Stage IV Prostate Cancer: Analysis from 40 Publicly Reported Anecdotal Cases (2024–2026)

Executive Summary

Background: Repurposed antiparasitic agents—ivermectin (IVM), fenbendazole (FBZ), and mebendazole (MBZ)—have generated public interest as potential adjunctive therapies in advanced malignancies, including stage IV prostate cancer. This narrative review analyzes 37 publicly reported anecdotal cases compiled in a 2025 Substack article (updated 2026) primarily sourced from Dr. William Makis’ X posts.

Methods: Cases were extracted from the source article, which organizes 22 core cases into drug-focused tables and lists 15 additional testimonials. Data abstraction focused on patient demographics, disease characteristics, treatment regimens, prior therapies, adjuncts, PSA kinetics, imaging outcomes, and clinical responses. Subgroup analysis was performed by primary regimen, background therapy, adjunct use, and response depth.

Results: All patients were adult males (ages 53–80) with Gleason 7–9 stage IV prostate cancer, predominantly bone-metastatic. The dominant regimen was IVM (1–1.5 mg/kg/day) + FBZ (1,332–2,000 mg/day), often with ongoing androgen deprivation therapy (ADT). PSA reductions of 90–99.9% within 3–6 months were reported in nearly all cases with available data, accompanied by radiological improvement (metastatic lesion shrinkage, resolution, or sclerotic healing) and symptomatic benefits (pain relief, restored mobility). Four exceptional responders included a paraplegic patient regaining ambulation. MBZ-inclusive regimens appeared in a minority.

Conclusion: These anecdotal reports demonstrate consistent patterns of rapid biochemical and radiological responses across subgroups. However, selection bias, lack of controls, and self-reported nature preclude causal inference. Formal randomized trials are warranted.

Keywords: prostate cancer, stage IV, ivermectin, fenbendazole, mebendazole, repurposed drugs, case series, subgroup analysis, PSA response, bone metastases

Introduction 

Stage IV (metastatic) prostate cancer carries a 5-year relative survival of approximately 37% under standard care, which typically includes androgen deprivation therapy (ADT), novel hormonal agents, chemotherapy, and/or radiation. Preclinical data suggest that benzimidazoles (FBZ, MBZ) and IVM may exert anti-cancer effects via microtubule disruption, apoptosis induction, and inhibition of tumor proliferation. Public testimonials, amplified on social media, have highlighted potential clinical activity in advanced prostate cancer.

This analysis reviews 37 anecdotal cases aggregated in the OneDayMD Substack article titled “Ivermectin, Fenbendazole and Mebendazole for Stage 4 Prostate Cancer: A Case Series of 22 Patients (2025),” with updates extending into 2026. The compilation draws heavily from Dr. William Makis’ X posts and related sources. The objective is to identify reproducible patterns and perform clinically relevant subgroup stratification to organize the initially unstructured testimonials. Note that a related 2025 case series by Makis et al. in Case Reports in Oncology (including one prostate cancer case) was subsequently retracted.

Methods

Data Source
The primary dataset comprises the 37 numbered case reports and three summary tables published in the referenced Substack article (August 9, 2025, with 2026 updates). Cases originate from patient/family self-reports posted on X (formerly Twitter) between 2024 and 2026.
Inclusion Criteria

• Adult male patients with documented stage IV prostate cancer.
• Use of IVM, FBZ, and/or MBZ (any dose/duration).
• Publicly available outcome data (PSA, imaging, or clinical status).

Data Extraction
Variables abstracted: age, geographic location, Gleason score, metastatic sites, drug regimen and dosing, prior/concomitant therapies (ADT, etc.), adjunct interventions, baseline and follow-up PSA, imaging findings, clinical symptoms, oncologist commentary, and follow-up duration.
Subgroup Analysis
Cases were stratified post-hoc by:

1. Primary drug regimen.
2. Background conventional therapy (ADT/hormone therapy vs. none/minimal).
3. Adjunct use (diet/supplements vs. none).
4. Response category (biochemical + radiological + clinical).

Descriptive statistics and representative vignettes are presented. No formal statistical testing was performed given the anecdotal, heterogeneous nature of the data.

Results

Patient Characteristics
All 37 cases involved men aged 53–80 years (median ~68) with stage IV, predominantly Gleason 9 prostate adenocarcinoma. Bone metastases were universal; additional sites included lymph nodes, liver, lung, and spine. Many patients had progressed on or were receiving ADT at repurposed-drug initiation.

Overall Patterns

• Rapid Response Phenotype: PSA declines of ≥90% (frequently 99.9% to near-undetectable levels) occurred within 3–6 months in cases with serial measurements.
• Radiological Improvement: Metastatic lesions frequently shrank, resolved, or became sclerotic/healed on bone scans, CT, or PET imaging.
• Clinical Benefit: Pain resolution, restored mobility (including one paraplegic patient ambulating), and improved performance status were commonly reported.
• Tolerability: Minimal side effects; treatments described as low-cost and self-administered.
• Oncologist Observations: Several reports noted physician surprise or unawareness of the repurposed agents despite objective improvements.

Subgroup Analysis
Table 1. Subgroup Stratification by Primary Drug Regimen

Subgroup	No. of Cases	Typical Regimen	Key Outcomes (Representative)
IVM + FBZ combination	~25 (majority)	IVM 1–1.5 mg/kg/day + FBZ 1,500–2,000 mg/day	PSA 531 → 0.19 (4 mo); bone mets healing (Case 31); PSA 0.12, near cancer-free (Case 37)
IVM + FBZ + MBZ	3–5	Triple antiparasitic	PSA 1,277 → 8.69 (4 mo, Case 32)
FBZ-dominant or IVM-dominant	Remainder	Single-agent emphasis (still often dual)	Comparable PSA/radiological responses

Table 2. Subgroup by Background Conventional Therapy

Subgroup	Characteristics	Outcomes
With ongoing/prior ADT	Most common; often progressed on Lupron, Orgovyx, Xtandi, etc.	Additive rapid PSA crash + scan improvement
Minimal/no systemic therapy (“abandoned” or hormone-naïve)	Cases 29, 31, 36, etc.	Equally robust responses; chemo avoided in several

Table 3. Representative Exceptional Responder Cases

• Case 29 (68yo, California, 2025): Paraplegic with vertebral destruction. IVM 1 mg/kg/day + FBZ 2,000 mg/day. PSA 217 → 0.19 at 5 months; metastatic bone pain resolved; regained ability to walk.
• Case 31 (66yo, Texas, 2025): Extensive bone metastases. IVM 70 mg/day + FBZ 1,554 mg/day. PSA 531 → 0.19 at 4 months; bones “healing greatly” on imaging; neurosurgeon initially assumed chemotherapy.
• Case 37 (75yo, Sweden, 2026): Gleason 9, bone + lung metastases. IVM 1 mg/kg/day + FBZ 1,500 mg/day + ongoing Casodex/Xtandi. PSA 0.12 at 5 months; scans showed “metastasis gone, only scars left; prostate cancer almost gone.”
• Case 32 (80yo, Saudi Arabia, 2026): Bone metastases. IVM + MBZ then FBZ. PSA 1,277 → 8.69 at 4 months; “remarkable” clinical response per physician.

Adjunct Therapies
A minority incorporated ketogenic diet, intermittent fasting, CBD oil, or high-dose IV vitamin C. These “hybrid” cases occasionally reported the fastest or most complete remissions, but the core antiparasitic regimen appeared sufficient in most pure cases.

Discussion 

The 40 cases exhibit striking homogeneity: rapid, multi-modal responses (PSA, imaging, symptoms) to IVM + FBZ (± MBZ) in heavily pretreated or treatment-refractory stage IV prostate cancer. Responses occurred irrespective of ADT background or geographic location (US, Canada, Sweden, Saudi Arabia). This consistency across subgroups suggests a potential class effect warranting mechanistic and clinical investigation.
Preclinical support includes microtubule inhibition and anti-proliferative activity. The observed synergy with ADT in many cases aligns with reports of enhanced efficacy in hormone-sensitive disease. Functional recoveries (e.g., paraplegia reversal) highlight possible quality-of-life benefits beyond biomarker changes.
Limitations

1. Anecdotal Nature: Self-selected positive outcomes; no denominator of non-responders or controls.
2. Heterogeneity: Variable dosing, compliance, scan timing, and reporting detail.
3. Bias: Social-media sourcing favors dramatic successes; publication/retraction of related formal case series underscores scrutiny needs.
4. Safety: While unreported here, rare liver injury has been noted with high-dose veterinary formulations elsewhere.
5. Causality: Concurrent ADT or spontaneous variation cannot be excluded.

These data do not constitute evidence of efficacy and must not replace standard-of-care therapy.

Conclusion

This subgroup analysis organizes 40 anecdotal stage IV prostate cancer reports into clinically meaningful clusters, revealing consistent patterns of rapid PSA decline, radiological improvement, and symptomatic benefit with IVM/FBZ-based regimens. While hypothesis-generating, the findings strongly support the urgent conduct of properly designed prospective clinical trials to evaluate safety, optimal dosing, and comparative efficacy against or in combination with established therapies. 

The current evidence base rests overwhelmingly on case reports and testimonials, which generate hypotheses but cannot establish causation or efficacy at the standard required for clinical practice. Until controlled trial data are available, patients and clinicians should rely on established, evidence-based therapies, with any off-label use of these agents considered only within structured research settings — including N-of-1 trial designs — under appropriate specialist oversight and informed consent.

Patients and clinicians seeking a deeper understanding are encouraged to review emerging research and consider participation in registered clinical trials. Patients considering off-label use should do so only under oncologist supervision. Treatment decisions should always be made in close consultation with a qualified oncology team.

Research and Institutional Perspective

From an institutional and research standpoint, the clinical signals observed across this 40-patient case series (stage 4 prostate cancer)—such as profound PSA reductions and radiologic clearances of metastatic lesions—provide hypothesis-generating evidence. 

However, because these findings remain classified as CEBM Level 4–5 evidence, academic institutions cannot establish definitive causality, efficacy, or generalizable safety profiles from individual case data. The strict institutional directive is that these compelling biological rationales must be translated into prospective, phase I/II randomized controlled trials to evaluate quantitative clinical endpoints like progression-free survival, overall survival, and predictive biomarkers.

Patient Perspective and Shared Decision-Making

For patients navigating a diagnosis as stage 4 prostate cancer—where standard-of-care front-line therapies often yield restricted median survival outcomes—time is a luxury they do not possess. This stark reality drives a massive unmet need for alternative therapeutic avenues, resulting in a high demand for accessible, affordable solutions when conventional lines of treatment fail or offer limited efficacy. 

Critics argue that big pharma should follow the big tech business model by providing both affordable and premium solutions, instead of investing massive capital exclusively into novel products paired with premium pricing. Diversifying this approach would allow established, repurposed compounds to fill urgent treatment gaps while high-end innovations continue to be developed. At present, the patient perspective emphasizes immediate quality of life, physical autonomy, and expanding options.

When incorporating these novel avenues, the medical, legal, and pragmatic landscape must be carefully navigated:

• Legality of Off-Label Prescribing: In most global legal frameworks, the off-label use of approved pharmaceuticals is an entirely legal and established practice. Physicians retain the legal authority to prescribe a drug for an unapproved indication if they determine it is in the best clinical interest of their patient and supported by emerging biological logic.

• The Peril of Self-Treatment: Under no circumstances should patients attempt to self-treat, source veterinary-grade alternatives, or self-administer antiparasitic protocols. Managing an advanced malignancy requires complex systemic tracking that cannot be safely duplicated at home. Do not self-treat.

• Accessing Expert Guidance: There are physicians around the world that operate telehealth practices offering integrative oncology consultation. This global network makes it possible to obtain expert insight into innovative drug repurposing strategies regardless of geographic limitations.

• The Indispensable Role of Medical Supervision: Patients must consult the right doctor to supervise use and oversee the entire therapeutic process. Ideally, the consultation should include your local doctor and oncologist. This collaborative approach ensures that conventional oncology and integrative strategies are fully aligned, preventing unsafe drug interactions while keeping care rooted in professional medical oversight.

• Rigorous Risk-Benefit Analysis: A collaborative risk-benefit analysis should guide every choice. The clinical team must balance the low toxicity and potential benefits demonstrated in case studies against potential side effects, interactions with conventional therapies, and the primary goals of care.

Ultimately, while institutions await the definitive data generated by clinical trials, patients facing advanced diagnoses require actionable solutions. Bridging these two perspectives requires structured, legally sound medical supervision, protecting patient safety while respecting their mandate to aggressively pursue every therapeutic tool available.

Frequently Asked Questions

Is there clinical trial evidence that ivermectin or fenbendazole treat prostate cancer?

As of mid-2026, no completed randomized controlled trials in humans have tested ivermectin, fenbendazole, or mebendazole specifically for prostate cancer. The evidence base consists of anecdotal case reports, social media testimonials, a small number of published case reports, and preclinical studies — hypothesis-generating, not confirmatory.

Why do case reports show dramatic PSA drops if the drugs are unproven?

Nearly all cases in this compilation combined fenbendazole or ivermectin with standard hormone therapy, chemotherapy, or radiotherapy independently capable of producing similar PSA declines. Self-selection bias (successes are shared; failures rarely are), absent controls, and lack of independent verification mean the relative contribution of the repurposed drugs cannot be isolated from these reports.

Are ivermectin and fenbendazole safe to combine with prostate cancer hormone therapy?

Short-term tolerability reported in these series was generally favorable at the doses used, but rigorous pharmacokinetic and drug-interaction data in cancer patients are lacking. Patients should not start or stop any therapy without discussing it with their treating oncology team, given the risk of undisclosed interactions and of delaying effective standard-of-care treatment.

What is the proposed mechanism of action for these drugs in cancer?

Proposed mechanisms include ivermectin's inhibition of WNT-TCF signaling and disruption of mitochondrial function and glycolysis, and benzimidazole-induced microtubule destabilization that can trigger apoptosis and potentially chemosensitize or radiosensitize tumor cells. These mechanisms are supported by in vitro and animal scientific evidence.

Disclaimer: Statements on this website have not been evaluated by the Food and Drug Administration. Content is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

This work does not constitute medical advice. Patients should consult licensed healthcare providers before initiating any treatment.

Acknowledgments: The authors acknowledge patients and advocates who shared their experiences on public platforms, and researchers including Dr. William Makis for documenting these cases.

References

1. World Economic Forum. Global cancer funding shortfall, 2024.
2. World Health Organization. Global cancer burden growing amidst mounting need for services, 2024.
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5. Mudassar F, et al. Targeting tumor hypoxia and mitochondrial metabolism with anti-parasitic drugs to improve radiation response in high-grade gliomas. J Neurooncol. 2020;147(2):393–403.
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7. National Cancer Institute SEER Program. Cancer Stat Facts: Prostate Cancer.
8. Case Reports in Oncology. Fenbendazole as an anticancer agent: case series, May 2025.
9. AI-modeled simulated randomized controlled trial: Ivermectin, Mebendazole, Metformin, High-Dose Vitamin C, Hyperthermia and More for Stage 4 Prostate Cancer (2025).
10. One Day MD. Fenbendazole and Ivermectin for Cancer: Real Stories, Science & Protocols (2025 Comprehensive Guide).
11. One Day MD. Ivermectin, Fenbendazole, and Mebendazole for Stage 4 Cancer: 310+ Case Reports Compilation (2026 Edition).
12. One Day MD. Fenbendazole and Ivermectin for Prostate Cancer Success Stories (including other stages of prostate cancer), 120+ case reports.
13. OneDayMD Substack. Ivermectin, Fenbendazole and Mebendazole for Stage 4 Prostate Cancer: A Case Series of 40 Patients (2026). https://onedaymd.substack.com/p/ivermectin-fenbendazole-and-mebendazole-3c9 (accessed May 2026).
14. Makis W, et al. Fenbendazole as an Anticancer Agent? A Case Series of Self-Administration in Three Patients. Case Rep Oncol 2025;18:856–863 (retracted).
15. Additional sources: Public X posts by Dr. William Makis (2024–2026) and related compilations.

Funding: None.
Ethics Statement: This is a secondary analysis of publicly available, de-identified anecdotal data; no IRB approval required.
This manuscript is presented in standard peer-reviewed journal format for illustrative purposes. It reflects a synthesized analysis of the provided source material and does not constitute original research or medical advice.

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© 2026 One Day MD. This article is for educational purposes only and does not constitute medical advice.