Fenbendazole

What fenbendazole is

Fenbendazole belongs to the benzimidazoles, a family of dewormers that also includes mebendazole and albendazole. It is approved for numerous animal species and acts against gastrointestinal roundworms, lungworms and tapeworms, including in cattle, sheep, horses, pigs and goats. The European assessment for veterinary medicines states that it is not used in human medicine.

Fenbendazole owes its reputation as a possible cancer drug to two strands. One is laboratory findings: in 2008, a research animal facility noticed that human lymphoma cells no longer grew in mice that received fenbendazole in their feed, and later cell experiments showed that it attacks the microtubules of cancer cells. The other is the story of Joe Tippens: he reported in a viral video that his metastatic lung cancer had disappeared after taking fenbendazole; at the same time he was receiving conventional cancer treatment. Since then, so-called fenben protocols have been circulating on social media (Krishnan 2026).

That a cheap, long-tested drug might also work against cancer is an understandable hope, especially for people with advanced disease. That makes it all the more important to look closely at what the data support and where they stop.

How it works

In parasites, benzimidazoles inhibit the assembly of tubulin into microtubules. Among other things, these tubes form the spindle apparatus that distributes the chromosomes during cell division. In addition, benzimidazoles block glucose uptake in worms, which makes the parasites’ energy supply collapse (Dogra 2018). In the mammalian body, fenbendazole is converted into oxfendazole, among other compounds, which is also an active benzimidazole.

Fenbendazole binds to mammalian tubulin with only moderate affinity. In human cancer cells it nevertheless disrupted the microtubule network and inhibited glucose uptake and the enzyme hexokinase II, on which many cancer cells depend for their energy. Whether the concentrations needed for this are reached in humans, and whether this translates into a benefit for people with cancer, is a separate question, and only studies in humans can answer it.

What the studies show

Cell experiments: a moderate microtubule inhibitor with several points of attack

In human lung cancer cells, fenbendazole bound to tubulin with moderate affinity and disrupted the microtubule network. At micromolar concentrations it killed cancer cells, moved the protective protein p53 into the mitochondria and inhibited glucose uptake, the glucose transporters (GLUT) and hexokinase II. Nude mice with human lung cancer xenografts that received fenbendazole orally for 12 days had markedly smaller tumours. The authors see this as a reason to investigate fenbendazole further as a cancer drug (Dogra 2018).

The chance finding with the vitamins

In a research animal facility, mice were treated against pinworms with fenbendazole feed, and an established model with human lymphoma cells suddenly stopped growing. The feed contained supplementary vitamins. In a targeted follow-up experiment with 20 mice in 4 groups, only the combination of fenbendazole and vitamins slowed tumour growth; fenbendazole alone or vitamins alone did not change it. The authors do not know the mechanism (Gao 2008).

No effect on mouse breast tumours

In cell culture, intensive treatments with fenbendazole were toxic to mouse breast cancer cells (EMT6), more so under oxygen deprivation. In the animal, however, fenbendazole did not change tumour growth even in maximally intensive regimens and did not enhance the effect of radiation. The authors found no evidence of a benefit in cancer therapy but consider the substance class worth further investigation (Duan 2013).

Case reports: a retracted series

In 2025, a case series was published on 3 people with advanced breast, prostate and skin cancer (melanoma) who had taken fenbendazole alongside other therapies but without chemotherapy. Two reportedly achieved complete remission and one near-complete remission. In January 2026, the publisher and editor retracted the paper: at the time of submission, the first author had offered services related to the topic and had not declared this as a conflict of interest (Makis 2025). In any case, single cases without a comparison group cannot show which part of a treatment worked.

How widespread use is

In early 2025, the combination of ivermectin and fenbendazole was recommended as a cancer treatment on a high-reach US podcast. An analysis of health records from 67 US healthcare organisations covering more than 68 million people shows that joint prescriptions of ivermectin and a benzimidazole almost doubled from January to July 2025 compared with the same period of the previous year (rate ratio 1.97); among people with cancer they rose 2.6-fold (Rockwell 2026). People who take fenbendazole without a prescription from veterinary products are not included in this analysis. More on the partner substance is on the page about ivermectin.

Registered trials

On October 14, 2026, ClinicalTrials.gov listed no trial that specifically tests fenbendazole in humans. It appears only in the long list of candidate drugs of a single-arm, non-randomized screening study from China that began in 2017, whose status has been unknown since 2019 and for which no results are available (NCT03299452).

Where the data stop

• A benefit for people with cancer. There is no controlled study in humans, neither on tumour response nor on survival. The only published case series with remissions was retracted.
• The transferability of the animal data. Positive and negative animal experiments contradict each other. Whether the concentrations effective in the laboratory are reached in humans can only be answered by studies in humans, and there are none.
• The Joe Tippens protocol. It rests on a single case who was receiving conventional cancer treatment at the same time. Which part worked cannot be separated this way.
• Safety in humans. Systematic safety data are lacking. What exists are case reports, and several of them describe severe liver injury.

Status, approval and legal

Fenbendazole is not approved as a medicine for humans in Germany, the EU or the USA. The European assessment for veterinary medicines states that it is not used in human medicine; in the USA it is approved only for animals (Thakurdesai 2024). For food from treated farm animals, maximum residue limits have been set in the EU.

Veterinary medicines containing fenbendazole are prescription-only in Germany: the German Prescription Drugs Ordinance (AMVV) lists fenbendazole “for use in animals” in Annex 1, and it may only be dispensed on a veterinary prescription. Products for animals are not intended for humans. Use against cancer is not approved anywhere.

Safety

In animals, fenbendazole is considered well tolerated and its acute toxicity is low. On repeated administration, however, rats and mice showed liver damage with elevated laboratory values and enlarged livers, and high doses affected the gastrointestinal tract and bone marrow. The European assessment names the effect on reproduction as the greatest concern: fenbendazole and related substances were teratogenic in several animal species. Like many benzimidazoles, it can act as a spindle poison and cause mis-segregation of chromosomes during cell division (EMEA/CVMP).

In humans there are only case reports, and several describe severe liver injury. A 67-year-old woman with a history of colon cancer came to hospital with jaundice; a biopsy confirmed severe hepatocellular injury, and her values normalized 3 months after stopping (Thakurdesai 2024). A 47-year-old woman with metastatic colon cancer on immunotherapy developed severe liver injury after increasing the amount she was taking herself. It initially looked like a side effect of immunotherapy, resolved quickly after fenbendazole was stopped, and immunotherapy could be continued without renewed liver injury (Krishnan 2026).

Important: Fenbendazole must not replace cancer treatment. If you take it or are considering it, tell your treatment team. Liver injury can interrupt ongoing therapy, and under immunotherapy it can be mistaken for an immunotherapy side effect, which can lead to unnecessary suppression of the immune system or treatment breaks (Krishnan 2026).

Sources

• Dogra N et al., Sci Rep 2018 – fenbendazole as a moderate microtubule inhibitor, cell experiments and xenograft mouse model
• Gao P et al., J Am Assoc Lab Anim Sci 2008 – unexpected tumour inhibition by fenbendazole only in combination with supplementary vitamins, lymphoma xenografts in SCID mice
• Duan Q et al., Anticancer Res 2013 – fenbendazole as a potential anticancer drug: no effect on EMT6 mouse breast tumours
• Makis W et al., Case Rep Oncol 2025 – case series of 3 patients self-administering fenbendazole, retracted (RETRACTED, retraction January 2026)
• Thakurdesai A et al., ACG Case Rep J 2024 – severe, histologically confirmed liver injury after self-administration of fenbendazole
• Krishnan A et al., World J Clin Cases 2026 – fenbendazole-induced liver injury under immunotherapy, differentiation from immunotherapy hepatitis
• Rockwell MS et al., JAMA Netw Open 2026 – prescriptions of ivermectin plus a benzimidazole after a podcast recommendation, 68 million patient records
• ClinicalTrials.gov NCT03299452 – single-arm screening study of drug combinations in advanced solid tumours (China), fenbendazole on the candidate list, status unknown
• EMEA, Committee for Veterinary Medicinal Products (CVMP) – Oxfendazole, Fenbendazole, Febantel, Summary Report (1): toxicology and maximum residue limits
• German Prescription Drugs Ordinance (AMVV), Annex 1 – fenbendazole for use in animals prescription-only