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Fenbendazole and cancer: what the evidence says

Animal studies and case reports suggest fenbendazole has some anti-cancer activity in cells and mice, but no human trial has tested it, the only PubMed case series of remissions was retracted, and most published human cases describe liver injury.

2/5 Preliminary

Animal studies, and at most single case reports in people. No controlled human trial on this outcome. How we score

A research summary, not a substitute for treatment. If you or someone you care for has cancer, talk to the oncologist before adding any supplement, and do not delay or replace treatment.

PubMed lists 82 papers on fenbendazole and cancer, and about 63 of them are lab or animal studies. Many found that it slows cancer cells by disrupting their internal scaffolding (microtubules) and their uptake of sugar, but several mouse studies found no effect on tumor growth, including two from Yale funded by the US National Cancer Institute.

No trial has ever been registered or published that tests fenbendazole in people with cancer. The human evidence is single cases: in a 2026 melanoma case, tumor markers fell and then rose again, and a 2025 series reporting remissions in three patients was retracted by its journal in January 2026 over an undeclared conflict of interest.

Six case reports in PubMed describe liver injury in people who took it, four of them people with cancer. In five of the six, liver tests recovered after they stopped.

A related human medicine, mebendazole, has been tested in small cancer trials, and one Swedish trial was stopped for lack of effect. Results for related drugs do not carry over to fenbendazole.

The evidence ladder higher rungs count for more
  1. Meta-analyses of trialspooled randomized trials0
  2. Human studiestrials and population studies0
  3. Case reportssingle people6
  4. Animal studiesmostly rodents19
  5. Lab studiescells, test tubes44

The studies in people, read one by one

ResultTypeWhat they didWhat they found
MixedCase report, 2026
1 people		Case report, metastatic melanoma, self-directed ivermectin + fenbendazole instead of standard treatment
Measured: Tumor response and circulating tumor DNA		Tumor DNA in the blood fell from 2.04 to 0.18 MTM/mL as the disease shrank, then rose to 0.93 as the main node grew again; the authors say spontaneous immune regression is at least as plausible as a drug effect. PubMed 42745863
PositiveCase report, 2025
3 people		Case series, advanced breast, prostate and melanoma, fenbendazole with other non-chemotherapy treatments
Measured: Remission		Reported two complete and one near-complete remission with no side effects. RETRACTED by the journal in January 2026 (PMID 41574240) for an undeclared conflict of interest; listed so the retraction is visible. PubMed 40605964
NegativeCase report, 2021
1 people		Case report, advanced lung cancer on pembrolizumab, one month of self-administered fenbendazole
Measured: Liver safety and tumor response		Severe liver injury that resolved after stopping; the patient had no tumor shrinkage. PubMed 34248555
NegativeCase report, 2026
1 people		Case report, metastatic colon cancer on nivolumab/relatlimab, self-increased fenbendazole dose
Measured: Liver safety		Severe hepatocellular liver injury rated probable (causality score 8); improved quickly after stopping, and immunotherapy was restarted safely. PubMed 41608149
NegativeCase report, 2025
1 people		Case report, patient on immunotherapy who took 2 g a day for a week
Measured: Liver safety		Tenfold rise in cholestatic liver tests with inflammation on liver biopsy; levels fell on their own about two weeks after admission. PubMed 41097960
NegativeCase report, 2026
1 people		Case report, prostate cancer, veterinary fenbendazole and ivermectin alternated daily for 3 months
Measured: Liver safety		Severe liver injury (ALT 1,764 U/L, bilirubin 12.9 mg/dL), rated highly probable for the two drugs (causality score 9); normal within 6 weeks of stopping. PubMed 42299164
PositiveReview, 2024Narrative review of pharmacokinetics, anti-cancer activity and toxicity
Measured: Overall evidence		Argues fenbendazole is promising from lab and animal work, notes that its human pharmacokinetics and safety are not well documented, and calls for clinical trials. PubMed 39197912

Where the sources agree, and where they don’t

1 of 7 kinds of source point toward a benefit, 2 toward no effect or harm, 3 are mixed, and 1 has no data yet. Agreement between independent kinds of evidence matters more than the number of papers in any one of them.

Kind of sourcePoints toDetail
Lab and animal studiesMixed63 papers; cell studies mostly positive, several mouse studies negative
Human trialsNo datanone registered or published
Case reports in PubMedMixed1 short-lived response; 1 remission series retracted
Case series outside PubMedPositive3 complete responses, 2 with other cancer treatment
Liver case reportsNegative6 people with liver injury, 5 recovered
FDA reportsNegative99 reports, 54 serious, 8 liver injury
Public reportsMixed18 of 40 say it helped, nearly all with standard treatment

Beyond Google: 8 findings about Fenbendazole from trial registries, FDA reports and patent offices that a normal search rarely shows. See them

What people report

We read public first-person posts and counted every outcome, good or bad. 40 reports about this condition, read on 2026-10-28; 4 mention side effects.

  • 18Helped
  • 8No effect
  • 2Got worse
  • 5Mixed
  • 7Too early

Why these counts prove nothing on their own: people who post are not a random sample, most take other treatments at the same time, and nobody checks the diagnosis. We show them because they tell researchers what to test next.

Read all 40 reports
  • Helped Tumor markers had been rising; about three weeks after starting, CA15-3 fell from 55 to 45, and a later test showed a further small fall. HealthUnlocked, 2019-09 (Still on Ibrance and fulvestrant; markers only, no scan yet; the poster is unsure fenbendazole caused it.)
  • Helped Reports a tumor marker falling from 109 to 32 over about a year of three-days-on, four-days-off use. HealthUnlocked, 2020 (On letrozole throughout; a later update describes markers falling again while she was off fenbendazole.)
  • Mixed After four weeks, a PET scan showed disease down about half but also a new bone metastasis; she cannot tell what is working. HealthUnlocked, 2019 (Started letrozole months earlier and takes several other supplements.)
  • No effect PSA rose from undetectable to 0.26 over nine months on the standard schedule; he concludes it has not worked for him. HealthUnlocked, 2020-03 (Stopped Lupron two months after starting fenbendazole, which can let PSA rise on its own.)
  • No effect Taking it since the previous December with no change in his rising PSA trend. HealthUnlocked, 2020-03 (PSA only; other treatment not described.)
  • Too early Took it for one month before starting chemotherapy; does not know whether it helped, and says it eased his constipation. HealthUnlocked, 2020-03 (Only one month before chemotherapy; no cancer result attributable.)
  • Helped With no other treatment, PSA fell from 2.27 to 1.5 over six months on high doses; liver tests stayed normal. HealthUnlocked, 2019-11 (PSA only, no repeat scan; other supplements added along the way. He later switched to mebendazole; a follow-up thread shows PSA 1.2 by mid-2020.)
  • Mixed Her husband's PSA fell from 13.4 to 10.1 in the first months, then kept rising slowly; he stopped when the bottle ran out. HealthUnlocked, 2019-11 (Caregiver report; on abiraterone at the same time; liver tests reported normal.)
  • Worse Her husband took about 1 g a day, several times the usual dose, and developed worsening cramps and diarrhoea, milder at a lower dose. Side effects: stomach cramps, diarrhoea. HealthUnlocked, 2019-11 (Caregiver report; no cancer result reported; dose far above what forums suggest.)
  • No effect Her husband took the usual small dose for 15 weeks; his last two PSA tests rose, so they stopped. No side effects. HealthUnlocked, 2019-11 (Caregiver report; PSA only.)
  • No effect Took the standard schedule and saw no result; in a later thread he says it never lowered his PSA. HealthUnlocked, 2019-11 (PSA only; other treatment not described.)
  • No effect Took it for over a year with no discernible effect and no noticeable side effects. HealthUnlocked, 2022-01 (No numbers given.)
  • Mixed PSA rose to 1.4, then fell to 0.5, and some small metastases left scan reports; he calls it neutral and still cannot tell. Side effects: brief diarrhoea, raised liver enzymes (ALT/AST), back to normal in two months. HealthUnlocked, 2022-01 (On Lupron throughout; later Provenge immunotherapy and radiation.)
  • Helped Took it alongside Eligard and responded very well, with lymph nodes clearing; he says he cannot credit fenbendazole. No side effects. HealthUnlocked, 2022 (Hormone therapy alone often produces large responses.)
  • Too early Took 444 mg a day for two weeks before a biopsy that found a small amount of cancer; no follow-up given. HealthUnlocked, 2023-12 (Two weeks; no earlier PSA for comparison.)
  • Helped Reports PSA falling from 143 to 26 in two months and to zero for the following four months, with no side effects. HealthUnlocked, 2024 (Does not say whether hormone therapy, standard at this stage, was also given; the post includes a phone number and promotional wording.)
  • No effect Took 222 mg rising to 880 mg a day for several months; PSA kept rising and a PET scan was unclear. HealthUnlocked, 2024 (PSA only.)
  • Helped PSA fell from 8 to 5 after 12 weeks; after he later stopped for two months, PSA was unchanged. HealthUnlocked, 2020-03 (PSA had already fallen from 12 to 8 before he started; PSA only.)
  • Helped After 50 days, PSA fell from 73 to 49, the large tumor on MRI shrank to under half its size, and urinary symptoms cleared. HealthUnlocked, 2020-03 (Short follow-up with no later update found; diet and DMSO also used.)
  • Helped Her partner's PSA fell from 300 to 3 in about four and a half months. HealthUnlocked, 2024-10 (Hormone therapy and enzalutamide started at the same time and usually lower PSA sharply.)
  • Too early Taking up to 2,000 mg a day with ivermectin; notices better urine flow and says time will tell. HealthUnlocked, 2023 (No test results given.)
  • Helped PSA fell from 6.3 to 1.9 three weeks after starting, and later to 0.6. HealthUnlocked, 2020-03 (Started Lupron shortly before; the poster agrees the fall could be the Lupron.)
  • Helped After about a year with half-dose Xtandi, PSA was 0.00 and he felt better; he does not know if fenbendazole was the cause. HealthUnlocked, 2020 (On enzalutamide throughout.)
  • Helped PSA had risen to 5.7; one week after starting fenbendazole it was 3.1, which surprised his oncologist. Inspire, 2022-05 (Only one week; on Lupron and Xtandi; he says he does not know the cause.)
  • Mixed After 4.5 years, PSA has not fallen (8 to 10), but a 2023 MRI showed no lesions where two earlier MRIs did. Inspire, 2023-11 (Different MRI methods across scans; PSA unchanged.)
  • Helped PSA fell from 6.0 to 4.2; he says fenbendazole was the only change. Inspire, 2023-11 (PSA only; his doctor was not told.)
  • No effect About eight months on the usual schedule: lesions very slightly smaller on MRI, PSA unchanged; he thinks it had no significant effect either way. Inspire, 2024-05 (Low-grade disease that often changes little.)
  • Helped Tumor markers halved each month after she started fenbendazole and then Xeloda. Inspire, 2019-08 (Chemotherapy started at nearly the same time; scan result not posted.)
  • Mixed Scans after several months showed stable disease, but her tumor marker kept rising; no side effects. Inspire, 2020-01 (On chemotherapy at the same time; lobular cancer is hard to see on scans.)
  • Too early In remission after surgery and chemotherapy; started it to prevent recurrence; no follow-up results posted. Inspire, 2019-06 (Already in remission when starting.)
  • Helped CA125 fell from about 1,200 to 19 and tumors shrank by half or more, which made surgery possible; no side effects in five months. Inspire, 2019-08 (Chemotherapy and bevacizumab at the same time.)
  • Helped PSA fell 30% after four weeks of the protocol; he then started hormone therapy. Inspire, 2019-07 (Four weeks; PSA only.)
  • Helped His wife's CA125 had been rising about 30% a month; after four weeks it was essentially unchanged. Inspire, 2019-09 (Caregiver report; four weeks; one marker reading.)
  • No effect After about two months she saw no change, good or bad, and paused because of stomach problems. Side effects: stomach problems. Inspire, 2019-12 (No test results given.)
  • Helped After chemotherapy plus eight weeks of daily fenbendazole, her PET scan was nearly clear and her surgeon found little disease. Inspire, 2020-02 (Standard chemotherapy at the same time.)
  • Too early Taking it daily with a targeted drug; a scan was pending. Inspire, 2024-12 (No result posted.)
  • Worse Took it to stay in remission; her liver enzymes rose and were normal again a month after stopping. Side effects: raised liver enzymes. Macmillan Online Community, 2026-01 (Liver result only; no cancer outcome; date approximate.)
  • Helped Tumors shrank and then stayed stable; he says he cannot tell whether fenbendazole, immunotherapy or the rest made the difference. Personal blog, 2025-11 (On immunotherapy; the site also asks readers for treatment donations.)
  • Too early Took it in the two months before surgery, which found clear lymph nodes; reports no ill effects. Inspire, 2025-01 (Surgery removed the tumor, so no effect of fenbendazole can be read.)
  • Too early Two weeks into the protocol before chemotherapy; feels better, but the tumor had not been re-imaged. Inspire, 2025-01 (Two weeks; no test results.)

Every other paper we found

PubMed returned 82 papers for this search on 2026-10-28. We read the human studies above ourselves. The rest are sorted by type automatically from PubMed's labels, which are sometimes wrong. We removed 8 papers that only share a word with this search.

Animal studies 19
  1. Synergistic anti-tumor effect of fenbendazole and diisopropylamine dichloroacetate in immunodeficient BALB/c nude mice transplanted with A549 lung cancer cells. Transl Lung Cancer Res, 2025
  2. Fenbendazole Exhibits Antitumor Activity Against Cervical Cancer Through Dual Targeting of Cancer Cells and Cancer Stem Cells: Evidence from In Vitro and In Vivo Models. Molecules, 2025
  3. Transcriptome analysis reveals the anticancer effects of fenbendazole on ovarian cancer: an in vitro and in vivo study. BMC Cancer, 2024
  4. Preparation and evaluation of fenbendazole methyl-β-cyclodextrin inclusion complexes. BMC Vet Res, 2024
  5. Fenbendazole Exhibits Differential Anticancer Effects In Vitro and In Vivo in Models of Mouse Lymphoma. Curr Issues Mol Biol, 2023
  6. An Update on the Biologic Effects of Fenbendazole. Comp Med, 2022
  7. HPMA Copolymer Mebendazole Conjugate Allows Systemic Administration and Possesses Antitumour Activity In Vivo. Pharmaceutics, 2022
  8. G2/M arrest and mitotic slippage induced by fenbendazole in canine melanoma cells. Vet Med Sci, 2022
  9. In vitro anti-tubulin effects of mebendazole and fenbendazole on canine glioma cells. Vet Comp Oncol, 2017
  10. Identification of epigenetically downregulated Tmem70 and Ube2e2 in rat liver after 28-day treatment with hepatocarcinogenic thioacetamide showing gene product downregulation in hepatocellular preneoplastic and neoplastic lesions produced by tumor promotion. Toxicol Lett, 2017
  11. Expression patterns of cell cycle proteins in the livers of rats treated with hepatocarcinogens for 28 days. Arch Toxicol, 2013
  12. Fenbendazole as a potential anticancer drug. Anticancer Res, 2013
  13. Disruption of Smad-dependent signaling for growth of GST-P-positive lesions from the early stage in a rat two-stage hepatocarcinogenesis model. Toxicol Appl Pharmacol, 2010
  14. Induction of GST-P-positive proliferative lesions facilitating lipid peroxidation with possible involvement of transferrin receptor up-regulation and ceruloplasmin down-regulation from the early stage of liver tumor promotion in rats. Arch Toxicol, 2010
  15. Crosstalk between PTEN/Akt2 and TGFbeta signaling involving EGF receptor down-regulation during the tumor promotion process from the early stage in a rat two-stage hepatocarcinogenesis model. Cancer Sci, 2009
  16. Cellular distributions of molecules with altered expression specific to the tumor promotion process from the early stage in a rat two-stage hepatocarcinogenesis model. Carcinogenesis, 2008
  17. Lack of modification of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)-induced hepatocarcinogenesis in rats by fenbendazole--a CYP1A2 inducer. Cancer Lett, 2002
  18. Liver tumor promoting effects of fenbendazole in rats. Toxicol Pathol, 1999
  19. [Intensity of liver tumor promotion effects in rats given repeated oral administrations of benzimidazole compounds]. Eisei Shikenjo Hokoku, 1996
Lab studies 41
  1. PEG-b-PCL Micelles as Nanocarriers for Poorly Soluble Benzimidazoles: A Comparative Study of Albendazole and Fenbendazole. Molecules, 2026
  2. Ferroptosis Induction by Fenbendazole Combined With Photothermal Therapy Triggers Dual-Immunotherapy Against Bladder Cancer. Adv Sci (Weinh), 2026
  3. Evaluation of the Drug-Polymer Compatibility and Dissolution Behaviour of Fenbendazole-Soluplus® Solid Dispersions Prepared by Hot-Melt Extrusion. Polymers (Basel), 2026
  4. Investigation of Fenbendazole Solubility Using Particle Size Reduction Methods in the Presence of Soluplus®. Pharmaceutics, 2025
  5. Fenbendazole induces pyroptosis in breast cancer cells through HK2/caspase-3/GSDME signaling pathway. Front Pharmacol, 2025
  6. Abemaciclib induces G1 arrest and lysosomal dysfunction in canine melanoma cells: synergistic effects with fenbendazole. Front Vet Sci, 2025
  7. Formulation and optimization of chitosan-based amorphous fenbendazole microparticles through a design of experiment approach. Int J Pharm, 2024
  8. Fenbendazole and Diisopropylamine Dichloroacetate Exert Synergistic Anti-cancer Effects by Inducing Apoptosis and Arresting the Cell Cycle in A549 Lung Cancer Cells. Anticancer Res, 2024
  9. Exploring the Dissolution, Solid-state Properties, and Long-term Storage Stability of Cryoprotectant-free Fenbendazole Nanoparticles. AAPS PharmSciTech, 2024
  10. Synergistic intravesical instillation for bladder cancer: CRISPR-Cas13a and fenbendazole combination therapy. J Exp Clin Cancer Res, 2024
  11. Network pharmacology and molecular docking study-based approach to explore mechanism of benzimidazole-based anthelmintics for the treatment of lung cancer. J Biomol Struct Dyn, 2024
  12. Anti-cancer effect of fenbendazole-incorporated PLGA nanoparticles in ovarian cancer. J Gynecol Oncol, 2023
  13. Anticancer Evaluation of Methoxy Poly(Ethylene Glycol)-b-Poly(Caprolactone) Polymeric Micelles Encapsulating Fenbendazole and Rapamycin in Ovarian Cancer. Int J Nanomedicine, 2023
  14. EZH2 as a prognostic-related biomarker in lung adenocarcinoma correlating with cell cycle and immune infiltrates. BMC Bioinformatics, 2023
  15. Redox-mediated Anticancer Activity of Anti-parasitic Drug Fenbendazole in Triple-negative Breast Cancer Cells. Anticancer Res, 2023
  16. Anti-cancer effects of fenbendazole on 5-fluorouracil-resistant colorectal cancer cells. Korean J Physiol Pharmacol, 2022
  17. Teaching an old dog new tricks: The case of Fenbendazole. Cancer Treat Res Commun, 2022
  18. Fenbendazole and its synthetic analog interfere with HeLa cells' proliferation and energy metabolism via inducing oxidative stress and modulating MEK3/6-p38-MAPK pathway. Chem Biol Interact, 2022
  19. β-Lactoglobulin-Modified Mesoporous Silica Nanoparticles: A Promising Carrier for the Targeted Delivery of Fenbendazole into Prostate Cancer Cells. Pharmaceutics, 2022
  20. Fenbendazole Suppresses Growth and Induces Apoptosis of Actively Growing H4IIE Hepatocellular Carcinoma Cells via p21-Mediated Cell-Cycle Arrest. Biol Pharm Bull, 2022
  21. In Silico and In Vitro Studies for Benzimidazole Anthelmintics Repurposing as VEGFR-2 Antagonists: Novel Mebendazole-Loaded Mixed Micelles with Enhanced Dissolution and Anticancer Activity. ACS Omega, 2022
  22. Benzimidazoles induce concurrent apoptosis and pyroptosis of human glioblastoma cells via arresting cell cycle. Acta Pharmacol Sin, 2022
  23. PEGylated Mesoporous Silica Nanoparticles (MCM-41): A Promising Carrier for the Targeted Delivery of Fenbendazole into Prostrate Cancer Cells. Pharmaceutics, 2021
  24. HPMA-Based Polymer Conjugates for Repurposed Drug Mebendazole and Other Imidazole-Based Therapeutics. Polymers (Basel), 2021
  25. Optimization and Pharmacokinetic Evaluation of Synergistic Fenbendazole and Rapamycin Co-Encapsulated in Methoxy Poly(Ethylene Glycol)-b-Poly(Caprolactone) Polymeric Micelles. Int J Nanomedicine, 2021
  26. Screening of Benzimidazole-Based Anthelmintics and Their Enantiomers as Repurposed Drug Candidates in Cancer Therapy. Pharmaceuticals (Basel), 2021
  27. Revisiting Activity of Some Nocodazole Analogues as a Potential Anticancer Drugs Using Molecular Docking and DFT Calculations. Front Chem, 2021
  28. Potential and mechanism of mebendazole for treatment and maintenance of ovarian cancer. Gynecol Oncol, 2021
  29. Unbiased Phenotype-Based Screen Identifies Therapeutic Agents Selective for Metastatic Prostate Cancer. Front Oncol, 2020
  30. Physicochemical, Pharmacokinetic, and Toxicity Evaluation of Soluplus® Polymeric Micelles Encapsulating Fenbendazole. Pharmaceutics, 2020
  31. Anthelmintics as Potential Anti-Cancer Drugs? J Korean Med Sci, 2020
  32. Benzimidazoles Downregulate Mdm2 and MdmX and Activate p53 in MdmX Overexpressing Tumor Cells. Molecules, 2019
  33. Drug library screen reveals benzimidazole derivatives as selective cytotoxic agents for KRAS-mutant lung cancer. Cancer Lett, 2019
  34. Fenbendazole acts as a moderate microtubule destabilizing agent and causes cancer cell death by modulating multiple cellular pathways. Sci Rep, 2018
  35. Investigating HIV-Human Interaction Networks to Unravel Pathogenic Mechanism for Drug Discovery: A Systems Biology Approach. Curr HIV Res, 2018
  36. Impairment of the ubiquitin-proteasome pathway by methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl)carbamate leads to a potent cytotoxic effect in tumor cells: a novel antiproliferative agent with a potential therapeutic implication. J Biol Chem, 2012
  37. Antiparasitic mebendazole shows survival benefit in 2 preclinical models of glioblastoma multiforme. Neuro Oncol, 2011
  38. Stimulation of pro-inflammatory responses by mebendazole in human monocytic THP-1 cells through an ERK signaling pathway. Arch Toxicol, 2011
  39. Unexpected antitumorigenic effect of fenbendazole when combined with supplementary vitamins. J Am Assoc Lab Anim Sci, 2008
  40. Mebendazole induces apoptosis via Bcl-2 inactivation in chemoresistant melanoma cells. Mol Cancer Res, 2008
  41. Transport of anthelmintic benzimidazole drugs by breast cancer resistance protein (BCRP/ABCG2). Drug Metab Dispos, 2005
Reviews 6
  1. Drug Repurposing in Veterinary Oncology: Myth or Reality? Vet Sci, 2025
  2. The Road to Precision Nanomedicine: An Insight on Drug Repurposing and Advances in Nanoformulations for Treatment of Cancer. AAPS PharmSciTech, 2025
  3. Exceptional Repositioning of Dog Dewormer: Fenbendazole Fever. Curr Issues Mol Biol, 2022
  4. The Antitumor Potentials of Benzimidazole Anthelmintics as Repurposing Drugs. Immune Netw, 2020
  5. Biologic effects of fenbendazole in rats and mice: a review. J Am Assoc Lab Anim Sci, 2007
  6. Immunomodulatory effect of various anti-parasitics: a review. Parasitology, 2006

Other conditions Fenbendazole has been studied for

Checked against PubMed on 2026-10-28. Everything we know about Fenbendazole