Question explored with the scientific record
Fenbendazole
The short version: fenbendazole is a well-studied animal dewormer with no proven benefit against cancer in humans and a documented case of severe liver injury.
The evidence you retrieved is almost entirely about fenbendazole killing worms in horses, goats, and cheetahs [1, 2, 3, 5, 6, 7, 10, 13]. It works for that, though resistance is widespread in some parasites [8, 10, 13]. The only human evidence is a single case report of an 80-year-old woman with lung cancer who took 1 gram of fenbendazole daily on a 3-days-on, 4-days-off schedule for a month [12]. She developed severe drug-induced liver injury. Her liver enzymes (AST and ALT) rose to roughly 16 to 30 times the upper normal limit. They normalized after she stopped the drug. Her tumor did not shrink [12]. The Naranjo score, a standard tool for judging whether a drug caused an adverse event, rated the link "probable" at 6 out of 13 [12].
The proposed mechanism for fenbendazole as a cancer treatment is borrowed from its action in parasites: it binds to tubulin and disrupts microtubule assembly, which can stop cell division [14, 19, 21]. That is a real mechanism. Many chemotherapy drugs work the same way. But a mechanism is not proof of safety or effectiveness in a human at a given dose. The evidence here contains no controlled trial, no case series, and no pharmacokinetic data showing what dose reaches a human tumor. The only human outcome data shows liver injury and no tumor response [12]. The burden of proof for using an unapproved veterinary drug in a human is extremely high, and this evidence does not come close to meeting it.
| Outcome | Evidence |
|---|---|
| Deworming in horses, goats | Effective, but resistance common [1, 2, 3, 5, 6, 7, 10, 13] |
| Human cancer treatment | No controlled trials; one case report shows no benefit [12] |
| Human safety | One case report of severe liver injury; no systematic safety data [12] |
My call: fenbendazole has no evidence of benefit against human cancer and a documented risk of severe liver injury. Do not take it. Confidence: high for the lack of benefit and the presence of risk.
Sources examined 23
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Anthelmintic efficacy on Parascaris equorum in foals on Swedish studs
This study investigates the efficacy of ivermectin, fenbendazole, and pyrantel against Parascaris equorum in foals on Swedish studs, revealing significant ivermectin resistance and recommending alternative treatments.
DOI: 10.1186/1751-0147-51-45 -
A study to evaluate the field efficacy of ivermectin, fenbendazole and pyrantel pamoate, with preliminary observations on the efficacy of doramectin, as anthelmintics in horses
This study evaluates the field efficacy of ivermectin, fenbendazole, pyrantel pamoate, and doramectin as anthelmintics in horses, revealing high efficacy rates for ivermectin and doramectin, while indicating potential benzimidazole resistance in fenbendazole at one site.
DOI: 10.4102/jsava.v71i3.703 -
Therapeutic efficacy of ivermectin, fenbendazole and albendazole against naturally occuring gastrointestinal nematodiasis infection in Black Bengal Goat of Bangladesh
Randomized controlled trial evaluating the efficacy of injectable ivermectin, and oral fenbendazole and albendazole against naturally acquired gastrointestinal nematodiasis in Black Bengal goats in Sylhet, Bangladesh, finding ivermectin most effective (100% EPG reduction and fav…
DOI: 10.14419/ijbr.v3i1.4267 -
Effect of the antiparasitic drugs fenbendazole and ivermectin on the soil nematode Pristionchus maupasi
This study investigates the ecotoxic effects of the antiparasitic drugs fenbendazole and ivermectin on the soil nematode Pristionchus maupasi, revealing that neither drug has acute toxic effects at naturally excreted concentrations in cattle dung.
DOI: 10.1016/j.vetpar.2004.06.003 -
Prevalence of strongyles and efficacy of fenbendazole and ivermectin in working horses in El Sauce, Nicaragua
This study investigates the prevalence of strongyle infections and evaluates the efficacy of ivermectin and fenbendazole treatments in working horses in El Sauce, Nicaragua, revealing high infection rates and effective treatment outcomes without signs of anthelmintic resistance.
DOI: 10.1016/j.vetpar.2011.04.002 -
Cyathostome fecal egg count trends in horses treated with moxidectin, ivermectin or fenbendazole
This study evaluates the efficacy of moxidectin, ivermectin, and fenbendazole in reducing cyathostome fecal egg counts in horses, finding that moxidectin was significantly more effective than the other two treatments over a 112-day period.
DOI: 10.1016/s0304-4017(01)00495-2 -
A field evaluation of anthelmintics for control of cyathostomes of horses in Brazil
This study evaluates the efficacy of ivermectin, piperazine citrate, and fenbendazole, both alone and in combination, for controlling cyathostome infections in horses in Brazil, revealing significant differences in treatment effectiveness and suggesting emerging resistance to ce…
DOI: 10.1016/0304-4017(91)90122-c -
Multiple anthelmintic resistance in a goat herd
A 30-month field study of a Virginia goat herd demonstrates widespread anthelmintic resistance in Haemonchus contortus to ivermectin, levamisole, and benzimidazole drugs, shows partial reversal of levamisole efficacy after withdrawal, reveals limited and variable efficacy of fen…
DOI: 10.1016/s0304-4017(99)00174-0 -
DIAGNOSIS-BASED TREATMENT OF HELMINTHS IN CAPTIVE AND WILD CHEETAHS ( ACINONYX JUBATUS )
A Namibia-based study at the Cheetah Conservation Fund evaluated parasite excretion in captive and wild cheetahs, tested the efficacy of routine deworming with fenbendazole, compared post-treatment parasite clearance between groups, and concluded that parasite loads can be manag…
DOI: 10.1638/2012-0028r1.1 -
An investigation of anthelmintic efficacy against strongyles on equine yards in S cotland
This study investigates the efficacy of three classes of anthelmintics against strongyles in equids on livery yards in Scotland, revealing widespread resistance to fenbendazole while demonstrating acceptable efficacy for pyrantel, ivermectin, and moxidectin.
DOI: 10.1111/evj.12079 -
Prevalence of gastrointestinal parasites in alpacas: A preliminary 1-year longitudinal study on a farm in Jeju, Korea
A year-long longitudinal study on a single alpaca farm in Jeju, Korea, assessing the prevalence and diversity of gastrointestinal parasites after fenbendazole treatment, revealing low overall parasite prevalence with evidence of reinfection pressure and implications for integrat…
DOI: 10.3347/phd.25042 -
Drug-Induced Liver Injury in a Patient with Nonsmall Cell Lung Cancer after the Self-Administration of Fenbendazole Based on Social Media Information
This case report describes an 80-year-old woman with advanced nonsmall cell lung cancer who developed severe drug-induced liver injury after self-administering fenbendazole based on social media information, with liver enzymes normalizing after cessation and no observed antitumo…
DOI: 10.1159/000516276 -
Anthelmintic resistance of horse strongyle nematodes to fenbendazole in Lithuania
Fenbendazole resistance among Cyathostominae in Lithuanian horse stables is widespread, with FBZ failing in several stables and showing variable FECRT results, underscoring the need for alternative parasite-control strategies.
DOI: 10.1186/s13028-022-00645-y -
Competitive Inhibition of High-Affinity Oryzalin Binding to Plant Tubulin by the Phosphoric Amide Herbicide Amiprophos-Methyl
This study investigates the competitive inhibition of high-affinity oryzalin binding to plant tubulin by the phosphoric amide herbicide amiprophos-methyl (APM), revealing that APM depolymerizes microtubules and inhibits tobacco cell growth through a substoichiometric mechanism.
DOI: 10.1104/pp.105.1.309 -
Regulation of the microtubule-lysosome interaction: activation by Mg2+ and inhibition by ATP
This study investigates the regulatory effects of ATP and magnesium ions (Mg2+) on the interaction between microtubules and lysosomes, demonstrating that Mg2+ activates and ATP inhibits this interaction, with implications for understanding intracellular transport mechanisms.
DOI: 10.1016/0167-4889(88)90158-9 -
Myelin-associated Glycoprotein Inhibits Microtubule Assembly by a Rho-kinase-dependent Mechanism
This study investigates how myelin-associated glycoprotein (MAG) and Nogo-66 inhibit microtubule assembly in neurons through a Rho-kinase-dependent mechanism, highlighting the role of collapsing response mediator protein-2 (CRMP-2) in this process.
DOI: 10.1074/jbc.M510934200 -
Disruption of microtubules in rat skeletal muscle does not inhibit insulin- or contraction-stimulated glucose transport
Disrupting microtubules in rat skeletal muscle does not block insulin- or contraction-stimulated GLUT4-mediated glucose transport, whereas nocodazole inhibits transport through a microtubule‑independent mechanism, suggesting microtubules are not essential for GLUT4 translocation…
DOI: 10.1152/ajpendo.00238.2002 -
Two new dammarane-type triterpenoids and other constituents from Gymnosporia diversifolia with anti-inflammatory and cytotoxic activities
Isolation of two new dammarane-type triterpenoids from Gymnosporia diversifolia and their anti-inflammatory and cytotoxic activities, supported by in silico docking and molecular dynamics suggesting a dual-target mechanism on tubulin and BCL-2 with compound 15 as the most promis…
DOI: 10.1039/d5ra07080e -
Antimitotic Sulfonamides Inhibit Microtubule Assembly Dynamics and Cancer Cell Proliferation
This study investigates the antiproliferative mechanisms of five indole sulfonamides, demonstrating their ability to inhibit microtubule assembly dynamics and induce apoptosis in HeLa cancer cells.
DOI: 10.1021/bi0523409 -
Conformation-Dependent Ligand Regulation of ATP Hydrolysis by Human KSP: Activation of Basal Hydrolysis and Inhibition of Microtubule-Stimulated Hydrolysis by a Single, Small Molecule Modulator
This study characterizes a novel small molecule modulator, KSPA-1, which activates basal ATP hydrolysis by human kinesin spindle protein (KSP) while inhibiting microtubule-stimulated ATP hydrolysis, providing insights into a new mechanism for targeting KSP in cancer therapy.
DOI: 10.1021/ja710889h -
Mechanism of Action of Tubulysin, an Antimitotic Peptide from Myxobacteria
This study characterizes the mechanism of action of tubulysin A, a cytotoxic antimitotic peptide from myxobacteria, showing that it inhibits tubulin polymerization, disrupts microtubule dynamics in cells, induces apoptosis, and competitively (noncompetitively) interferes with vi…
DOI: 10.1002/cbic.200500421 -
MOLECULAR MOTORS CONTROL LENGTH OF ANTIPARALLEL MICROTUBULE OVERLAPS
This study uses Monte Carlo simulations to investigate how molecular motors, specifically Xklp1, regulate the length of antiparallel microtubule overlaps in the presence of PRC1, proposing two models of inhibition mechanisms and concluding that the allosteric inhibition model al…
DOI: 10.1142/s0217984911500278 -
Role of microtubule actin crosslinking factor 1 (MACF1) in bipolar disorder pathophysiology and potential in lithium therapeutic mechanism
This is a narrative review synthesizing evidence that microtubule actin crosslinking factor 1 (MACF1) plays a central role in bipolar disorder pathophysiology through cytoskeletal regulation, neuronal development, immune signaling, and mitochondria, and may mediate aspects of li…
DOI: 10.1038/s41398-023-02483-6