Is Fenbendazole Safe And Effective?
Pushback arrived after the recent interview with William Supple, but his views on fenbendazole and cancer are more accurate than the criticisms, and his book is definitive
The objections and the rebuttals from his book Cancer Is a Parasite (2026) follow. Supple also wrote an email about these issues that appears in Part 3.
Oncology is a vast industry, and its corrupt toadies have every motivation to destroy the credibility of repurposed drugs like these. That said, better evidence than this sad fact follows.
Supple’s central claims that benzimidazole-based parasite drugs have anticancer activity are supported by dozens of preclinical studies. The mechanisms are known: microtubule disruption, p53 reactivation, Warburg effect interference, angiogenesis inhibition, and cancer stem cell targeting.
Case reports are not proof of a reliable cancer cure, but they are all we have in our age of pharmaceutical study fraud and information suppression. As Paul Marik says, “A thousand case reports are data.”
Fifty sequential case reports are substantial evidence. Fenbendazole’s numbers are in the thousands.
The cautious conclusion about fenbendazole is that although it is not universally effective against all cancers, adding it to protocols is wise, and adverse consequences are unlikely. As BCC told me, “When your life is on the line, you throw out all your hand grenades at once.”
Pick up a copy of Supple’s book HERE to learn more.
Part 1: Why are cancer patients shopping at Tractor Supply?
People with cancer are buying dog dewormer at farm supply stores because the system designed to help them has failed them.
They are doing this not because they are stupid but because they looked at what conventional oncology offers for most cancers, the price, and the survival data, and concluded that a fifty-pound bag of antiparasitic medication for under a dollar a dose was a more rational bet.
Fenbendazole is the best studied drug of its class, but clinical trials have not been done
The benzimidazole anthelmintics include fenbendazole, mebendazole, and albendazole. They share a core structure: a benzene ring fused with an imidazole ring. They all bind beta-tubulin and disrupt microtubule formation. Their anticancer properties overlap, but they are not identical.
Mebendazole is FDA-approved for human use and is available in the United States as a prescription medication (Emverm) and through compounding pharmacies, as well as in veterinary formulations.
The WHO includes it on its List of Essential Medicines. It has decades of human pharmacokinetic data, including long-term high-dose studies in patients with echinococcosis at 40 to 50 mg/kg/day for months to years.
It crosses the blood-brain barrier, and polymorph C mebendazole reaches therapeutic concentrations in brain tissue in preclinical glioblastoma models. For patients with primary brain tumors or brain metastases, this property is significant.
Fenbendazole is approved for veterinary use and lacks formal human pharmacokinetic studies. It is available over the counter at farm supply stores and online for pennies per dose. This accessibility drove its adoption by the cancer patient community.
The standard dose of 222 mg was entered into human use by accident, as the dose for a ten-pound dog, and stuck because it worked.
The Kory clinic and others favor mebendazole based on cell-line potency comparisons. IC50 (the concentration required to inhibit 50 percent of cell growth) is lower for mebendazole in melanoma cells: 0.30 to 0.32 micromolar versus 1.2 to 1.4 micromolar for fenbendazole.
A lower IC50 means less drug is needed to kill the cancer cells.
Supple and Nguyen et al. (2024) make a different argument. Fenbendazole hits a metabolic axis that mebendazole does not attack as aggressively.
Fenbendazole simultaneously destabilizes tubulin, causes mitochondrial translocation of p53, inhibits glucose uptake, downregulates GLUT transporters, and suppresses hexokinase II, a key glycolytic enzyme that most cancer cells depend on.
The Nguyen review in Anticancer Research states that fenbendazole “surpasses albendazole and mebendazole in treating drug-resistant cells” and attributes this superiority to its glycolytic inhibition.
This distinction is medically important. Patients who have exhausted standard chemotherapy are, by definition, dealing with drug-resistant cancer cells. Fenbendazole’s metabolic attack on glycolysis targets a vulnerability that microtubule disruption alone does not.
As Supple writes in Cancer Is a Parasite:
“By blocking glucose and slashing lactate production, fenbendazole dismantles a key engine of tumor growth and drug resistance. This potent metabolic attack offers a powerful way to kill cancer cells that have become resistant to traditional chemotherapy drugs.”
The case reports support this. Many of the documented fenbendazole responders, including the 362 cases compiled by OneDayMD and the 22 detailed in Supple’s book, were patients discharged to hospice after exhausting standard treatment.
They were in the throes of drug-resistant disease. That fenbendazole worked where conventional drugs had failed is consistent with its glycolytic mechanism.
No clinical trials comparing fenbendazole to mebendazole for cancer exist. The IC50 data favor mebendazole in some cell lines. The metabolic mechanism data favor fenbendazole against drug-resistant cells.
Cancer at one month is different from the same cancer at one year, and the effectiveness of different agents varies over time. Patients and physicians should know both drugs, understand their respective advantages, and recognize that the definitive comparison has not been done.
Taking either drug, or both, alongside other interventions, is the strongest position available with current evidence.
The peer-reviewed Baghli, Martinez, and Marik protocol published in September 2024 recommends mebendazole at 200 mg per day for low-grade cancers, 400 mg per day for intermediate-grade, and 1,500 mg per day for high-grade cancers.
For fenbendazole, the protocol specifies 1,000 mg three times per week for high-grade cancers, with 222 mg daily as the baseline dose supported by the largest number of case reports. Both drugs should be taken with fatty food.
The liver risk
A paper warning about fenbendazole and liver damage by Yamaguchi et al. (2021) appears first on most search results for this topic. Search ranking at that scale does not happen by accident when money is at stake.
Supple reviews this paper in his book and identifies a serious confound: the patient was also taking pembrolizumab (Keytruda), an immunotherapy drug that lists hepatic damage as a major side effect.
She had been on pembrolizumab for months before trying fenbendazole for one month. Whether the accumulated immunotherapy caused the liver enzyme changes, an interaction between the two drugs occurred, or fenbendazole-induced tumor lysis produced the transient elevations is unknown.
The Yamaguchi paper does not resolve this question.
Supple tracked his mother-in-law’s ALT (alanine aminotransferase) and AST (aspartate aminotransferase) alongside her tumor markers throughout treatment. When she started fenbendazole, her liver enzymes were normal.
As her tumor markers dropped over the first two months, her enzymes rose to around 150 (the normal ceiling is roughly 30). Then, while she continued on fenbendazole without interruption, they returned to normal and stayed there.
If fenbendazole were hepatotoxic, the enzymes would have stayed elevated for as long as she took it. They did not. The transient spike coincided with the active cancer-killing phase and resolved without stopping the drug.
The explanation Supple offers: as fenbendazole destroyed billions of cancer cells, the cellular debris flooded the bloodstream and passed through the liver for processing. The liver was working hard. It was not being poisoned.
This pattern is consistent across Supple’s 22 detailed case reports. None showed chronic elevations in liver enzymes from fenbendazole. In one case (RGR), transient ALT/AST elevation coincided with fulvestrant administration, whereas fenbendazole alone produced no fluctuations in liver enzymes over 8 months of continuous use.
Another case (BK) showed no detectable hepatotoxicity despite concurrent use of multiple agents.
Separate case reports in the gastroenterology literature document more severe liver injury in patients who self-administered fenbendazole without monitoring, in one case at doses 10 times the standard amount, and in 2 cases involving patients with pre-existing liver disease or concurrent immunotherapy.
These cases are overdosing, drug interactions, or compromised livers rather than a class effect of fenbendazole at the standard 222 mg dose.
Monitor liver enzymes at baseline, at 4 weeks, at 8 weeks, and monthly thereafter during cancer treatment. A transient rise is expected and indicates activity, not damage. Persistent elevation, jaundice, or coagulopathy are signals to stop.
Patients with pre-existing liver disease or those taking other hepatotoxic drugs should exercise extra caution. Do not take fenbendazole with acetaminophen (Tylenol), which depletes the liver’s glutathione defense. Pregnant women should avoid it.
These drugs are not monotherapy and not replacements for conventional treatment
Every credible source working with repurposed antiparasitics for cancer agrees on this, including Supple. Pierre Kory and Paul Marik classify benzimidazoles as Tier One repurposed drugs but use them alongside ivermectin, metabolic interventions, and conventional treatment in supervised multi-drug protocols with cycling to prevent resistance.
Three case reports from Stanford showing the benefits of fenbendazole involved patients who received it alongside androgen deprivation therapy, radiation, and multi-agent chemotherapy.
The original Joe Tippens case, which launched the entire movement, has a confound: Tippens was concurrently receiving pembrolizumab (Keytruda) in a clinical trial. His remission could have resulted from the immunotherapy.
Supple is careful to recommend taking fenbendazole alongside conventional therapy rather than as a substitute. He stresses that every situation is unique, that all options should be considered, and that no one should interpret his work as an argument for abandoning other treatments.
Part 2: Cancer therapy is an outrageous scandal
Patients with cancer are desperate because the system that is supposed to help them is a mess. The evidence for this is a peer-reviewed paper published in Clinical Oncology in 2004, and nobody has refuted it in 22 years.
The 2.1 percent
In 2004, Morgan, Ward, and Barton published “The Contribution of Cytotoxic Chemotherapy to 5-Year Survival in Adult Malignancies” in Clinical Oncology. They examined 22 major adult cancers using randomized controlled trial data and cancer registry data from Australia and the United States.
They calculated the absolute contribution of cytotoxic chemotherapy to 5-year survival for each cancer type, then summed the results.
The overall contribution of curative and adjuvant cytotoxic chemotherapy to 5-year survival in adults was 2.3 percent in Australia and 2.1 percent in the United States.
The 5-year survival rate for cancer in Australia at the time was over 60 percent. Chemotherapy contributed 2.3 percent of that. Surgery, early detection, and the natural history of indolent cancers accounted for almost everything else.
The cancers where chemotherapy produces meaningful survival benefit are Hodgkin’s lymphoma, testicular cancer, some non-Hodgkin lymphomas, childhood acute lymphoblastic leukemia (ALL), and small adjuvant benefits in breast, colon, and ovarian cancer.
Five to six diseases. Since 2004, targeted therapies have added a few more: imatinib transformed chronic myeloid leukemia (CML), and immunotherapy checkpoint inhibitors have produced durable responses in melanoma, some lung cancers, and renal cell carcinoma.
Call it eight to ten entities total. For the remaining majority of adult cancers, cytotoxic chemotherapy does not extend life.
In lung cancer, median survival increased by only 2 months over 20 years of new drug development. The Morgan paper concluded that a rigorous evaluation of the cost-effectiveness of cytotoxic chemotherapy was urgently required.
The medical oncology community responded with outrage but no data. Twenty-two years later, no one has published a definitive counter-analysis. That silence is not an accident.
Radiation therapy has the least support
Barton et al. published a systematic review in 2017 estimating the population-level benefit of evidence-based radiotherapy. Radiotherapy provides a 5-year overall survival benefit in 2.4 percent of all cancer patients.
Adding concurrent chemoradiation provides an additional 0.3 percent. The total: 2.7 percent, for a specialty that treats nearly half of all cancer patients.
Radiation has a supposed survival benefit in cervical cancer, head and neck cancers, certain lung cancers, some rectal cancers, and prostate cancer.
For breast cancer, post-mastectomy radiation improves cancer-specific survival but simultaneously decreases non-breast cancer survival through cardiovascular toxicity.
The net effect on overall survival is roughly a draw.
This is taken from a long document. Read the rest here substack.com
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