Ivermectin, Fenbendazole, and Mebendazole in Stage IV Prostate Cancer: Case Series Review and Subgroup Analysis from 37 Publicly Reported Anecdotal Cases (2024–2026)

Abstract

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.
Conclusions: 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 37 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 37 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. Patients considering off-label use should do so only under oncologist supervision.
References:

1. OneDayMD Substack. Ivermectin, Fenbendazole and Mebendazole for Stage 4 Prostate Cancer: A Case Series of 22 Patients (2025). https://onedaymd.substack.com/p/ivermectin-fenbendazole-and-mebendazole-3c9 (accessed May 26, 2026).
2. 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).
3. 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.