An article published by the BBC this week tells the worrying story of a stairlift salesman offering to sell a vulnerable cancer patient two unproven treatments for cancer unprompted. Following a tip-off, the BBC put an undercover reporter on the story, and the salesman, who they identified as Jason Sarver, confirmed to the reporter, “I’m not a doctor, I just pass what I hear on,” before offering to sell the reporter a 3-month supply of ivermectin and fenbendazole for £100 to treat cancer. The article goes on to describe how other cancer patients ignored desperate pleas to seek medical help from their loved ones, instead opting to take these drugs before they died. The BBC also reports the ease with which they were able to illegally obtain the drugs on sites such as Amazon.
Ivermectin is a very effective treatment for several human and animal parasites, while fenbendazole is used as a dewormer in veterinary medicine. Neither is licensed as a cancer treatment by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) or the FDA in the US (so far!).
In recent years, the two medicines have been widely promoted as miracle cancer drugs in alternative health circles – perhaps most prominently by Mel Gibson on a January 2025 appearance on the Joe Rogan Experience podcast. This is despite there being “zero real-world clinical evidence” to support ivermectin’s use as a cancer drug, as Macmillan Cancer Support told the BBC. In the past two years, I have seen dozens of websites, Telegram channels, and Twitter accounts promoting the drugs and providing “protocols” for patients to use.
Ivermectin first gained major prominence outside veterinary clinics and global health circles during the Covid-19 pandemic, when it was trumpeted as a possible miracle treatment for the disease. This process of taking a treatment for one disease and using it to treat another is termed ‘drug repurposing.’ Ivermectin has been no stranger to repurposing, as over the past forty years of its use, it has been studied for dozens of diseases.
While research interest in ivermectin’s purported antiviral properties had been ongoing prior to 2020, it exploded during the Covid-19 pandemic. This is also where my connection to the medicine started. In 2021, I was a master’s student at St George’s, University of London (now City St George’s) and had been given an assignment to critically appraise a preprint paper which had been widely cited to support the proposition that ivermectin acted as a ‘miracle’ cure and preventative for Covid-19.
Upon a close read, I quickly realised the paper’s introduction had been plagiarised almost in its totality – largely by aggressively running sentences from other papers through a thesaurus with little regard to the mangling they would suffer as a result. In fact, the authors did not even notice their approach had transformed the name of the virus which causes Covid-19 from “severe acute respiratory syndrome” to “extreme intense respiratory syndrome.”
Worse awaited me when I, together with several scientific fraud experts, examined the paper’s underlying data and concluded that it was mathematically impossible. In fact, so brazen was the authors’ attempt to cook the books that the dataset even included a data point from the 31st of June (a date which does not exist). After these points were raised publicly, the preprint was quickly retracted, as were some of the review papers citing it. And I achieved a mark of 72% for my university assignment.
Following on from this success, my colleagues and I investigated several other papers purporting to show benefits for taking ivermectin for Covid-19 and found several glaring errors in these too. As it stands, the weight of the evidence suggests ivermectin has little or no effect in treating or preventing Covid-19 (though you will find many dissenting voices vociferously saying otherwise).
Following my forays into the ivermectin literature, I came away having grown fascinated by the drug. It is far more than just a “horse dewormer” or, as several people in my life have mistakenly said, a “horse tranquiliser” (that would be xylazine, itself often being mistaken for ketamine). In fact, I became so fascinated by ivermectin that I have spent the past 5 years studying its effects on cancer during my master’s and (still-in-progress) PhD.
Due to the ivermectin wars during the Covid-19 pandemic, ivermectin has unfortunately gained a relatively negative valence within skeptical circles; I think this is just as unwarranted as the “miracle cure” hype about the drug. It is not the drug itself that is the problem but those using it for their own ends.
Indeed, the embrace of ivermectin by the alternative health community is a great irony given its origin as a big pharma wonder drug. Its precursor molecule was discovered in a soil sample in Japan by Satoshi Ōmura and was later developed in the US by William Campbell of Merck. It quickly revolutionised the treatment of several parasitic diseases in animals and later humans – particularly in the global South. In 2015, the two discoverers of the drug were awarded a Nobel Prize in medicine for their work (alongside Tu Youyou for her work on artemisinin).
In many ways, ivermectin is an excellent drug: highly effective for its intended purpose, incredibly cheap to manufacture, and very safe (unless you’re a collie dog). Given its success and dirt-cheap manufacturing cost, Merck has donated 4.4 billion doses of the drug to treatment programmes worldwide since 1987.
Ivermectin and cancer: the evidence
I am far from the only one in the scientific community studying the effects of ivermectin in cancer. There has been interest in the drug in cancer research circles since at least the early 2000s, but despite a slew of promising laboratory results, no clinical trial has yet confirmed any clinical benefit.
While I would love to come away from my years of work with a simple answer to the question of whether ivermectin cures cancer, I unfortunately have not. In laboratory dishes ivermectin certainly kills cancer cells, substantially boosts the efficacy of several other more conventional chemotherapy drugs, and appears to act through plausible mechanisms. Evidence from animal studies and across several tumour types paints a similarly rosy picture. Nonetheless, I am left with strong doubts.
As already stated, to date no large-scale clinical trial has been conducted to assess the effects of ivermectin on cancer. There is one extremely dubious observational study published in the journal of Anticancer Research in June 2026 involving 197 patients (though 38.1% did not complete follow-up). The study relies on patient self-reported outcomes, has no control group or radiological confirmation, and was conducted by a platform that sells ivermectin to cancer patients. The study also cites a paper on fenbendazole which had already been retracted at the time of publication. The journal’s editors have since launched an investigation into the paper’s data integrity and ethical oversight and slapped a prominent Expression of Concern on it. Beyond this questionable study, two small-scale trials are currently recruiting patients.
Therefore, the remaining evidence currently available is anecdotal social posts, podcast appearances, or laboratory-based research. Unfortunately, the anecdotal evidence is quite mixed. While some anonymous Twitter users claim great success, Scott Adams, the right-wing political commentator and creator of the Dilbert cartoons, experimented with using ivermectin and fenbendazole to treat his metastatic prostate cancer before later declaring the drugs had no effect and subsequently passing away.
An ineffective medicine having no effect is the best outcome in the circumstances. In worst-case scenarios, the ineffective drug may hasten the course of the patient’s disease or interfere with other treatments the patient is taking.
Ivermectin is broken down in the liver by an enzyme called CYP3A4 (responsible for the grapefruit warning on some prescription medication). It also breaks down many other drugs, including cancer treatments such as docetaxel and the prostate cancer drugs abiraterone and enzalutamide (incidentally, drugs Scott Adams may have been prescribed for his tumour). Because ivermectin competes for the same enzyme, a patient’s other medications may be cleared faster or slower than their oncologist intended, leading to a patient having too little of a drug that was working, or too much of one that is toxic at high concentrations.
More directly, high doses of ivermectin (and most protocols circulating online use high doses) have been known to cause ataxia, seizures and coma in patients. This risk is heightened in some patients due to specific gene mutations affecting the blood-brain barrier.
Perhaps most importantly, oncologists are always working against a clock. Patient outcomes tend to be better the earlier a tumour is identified, and the clock doesn’t pause while patients seek out alternative treatments.
Regarding the laboratory evidence, skeptical readers will no doubt be familiar with the XKCD comic which succinctly makes the point “When you see a claim that a common drug or vitamin kills cancer cells in a petri dish, keep in mind: So does a handgun.”
When studying a drug in a laboratory, scientists often start with a cell-level model of cancer. We focus on cancer cells grown in a nutrient broth a few million at a time, then stick drugs on them and watch what happens at the whole-cell or molecular level. This greatly simplifies things experimentally and is an excellent starting point. Unfortunately, it comes with the minor inconvenience of ignoring the other 30ish trillion cells that make up the average human.
This stripping away of biological detail goes some way to explaining why very few scientific findings successfully make the transition from laboratory to clinical care, and why just about everything appears to cure or cause cancer (according to newspaper headlines at least). When you strip away detail to model a disease more simply, you risk drawing overly optimistic or pessimistic conclusions from your data.
Related to this, the ivermectin dose most researchers use in the laboratory far exceeds the doses used safely in clinical settings. While animal studies show that potentially safe doses can have positive effects, there is still a significant difference between a laboratory mouse and a human cancer patient.
Another problem with the search for a miracle “cancer” cure is that cancer is not one disease but many. Different cancers in even the same organ can have widely different outcomes, and each arises for different reasons. A person claiming a cure for “cancer” should be looked at with just as much skepticism as one who says they have a tyre that fits every vehicle.
Unfortunately, we have also been here many times before. Ivermectin is not the first drug with highly exciting pre-clinical evidence.
Scientific history is replete with examples of other drugs that have been hailed as possible repurposed cancer cures and then failed spectacularly. One relatively recent example is the first-line diabetes drug metformin. Early laboratory and animal studies showed strong support for its use in cancer care, but when human trials materialised, the benefit proved absent. This is the norm, not the exception, with repurposed drugs. There is little reason to expect ivermectin to buck this trend. However, despite this – and perhaps blinded by my fascination with the drug – I am certainly not against well-conducted clinical trials testing it.
While those in conspiracy circles have much to reckon with, those of us in the skeptical or scientific community must also wrestle with our reflexive dismissal of ivermectin. Patients are clearly interested and laughing off ivermectin as just a “horse dewormer” is not an effective counter. We need to treat patients with empathy, understanding, and curiosity. Ivermectin is a damn good drug, and we can acknowledge that without buying into any claims about its efficacy in treating cancer.
The grifters selling ivermectin on Amazon or Twitter aren’t just selling pills; they’re selling hope, so we should provide our own hope. It’s sometimes underappreciated how much cancer outcomes have improved over the past 50 years, and early and ongoing engagement with an oncologist is far better than turning up with metastatic cancer once you have tried everything else.
Unfortunately, until clinical trials start reporting results, we won’t know for certain whether ivermectin can help improve cancer outcomes. But until then, let’s try to remember that good medical advice typically arrives via a peer-reviewed paper, not a stairlift.
