A common deworming drug used in dogs and cats may help to cure cancer in humans, but doctors urge caution over the unproven method.
Fenbendazole, known by its brand names Panacur and Safe-Guard, is an antiparasitic used in animals with parasites such as roundworms, hookworms, tapeworms and giardia.
But in recent studies that investigated its efficacy in treating cancer in humans, researchers said it could be a ‘potentially safe and effective’ alternative treatment.
In a video last month, Dr John Campbell — a former nurse educator in the UK — reviewed case studies from 2021 that found three patients with advanced cancer saw their tumors shrink after taking fenbendazole.
He said: ‘I think the drug regulators need to start looking at this as a matter of some urgency because people are dying from cancer now.
‘If something is safe and effective, surely it can be accredited for human use by our national authorizing agencies pretty quickly — if they wanted to.’
A handful of scientific papers have been published in recent years suggesting fenbendazole has anti-cancer properties — including a 2020 review from scientists in Tennessee, which found the drug slowed lung cancer growth in some mice with the disease.
Another study from this year that reviewed six human cases where tumors shrank after taking the drug concluded fenbendazole ‘stands out’ as a possible new cancer therapy.
A common deworming drug used in dogs and cats may help to cure cancer in humans, according to studies and anecdotal reports (stock image)
The above image shows a packet of fenbendazole for animals sold on Amazon. It had 2,000 purchases in the last month
Anecdotal reports from users on TikTok, YouTube and X also suggest the drug can help, with several users crediting it with ‘curing’ their cancer.
But despite the growing body of evidence, medical non-profits currently warn against using the drug — pointing out it has never been tested in large scale human clinical trials, the gold standard for showing a treatment is safe and effective.
And it is not without risks. Doctors in South Korea — which saw a surge in people taking the drug to combat cancer in 2019 — said it left some patients with intestinal necrosis, a severe medical condition where part of the intestine dies.
In October this year, a 45-year-old British man was reported to have died from liver failure after taking the drug for its alleged anti-cancer properties.
Dr Jason Williams, who uses experimental treatments for cancer patients, told DailyMail.com: ‘Fenbendazole may be useful in specific contents, but it is a double-edged sword.
‘In some cases, it could even promote cancer growth if not applied appropriately.
‘Its use must be carefully tailored to the individual patient’s situation and monitored closely.’
Fenbendazole costs about $9 for a week’s supply and is available over-the-counter and online for dogs in liquid, powder or paste form.
Owners give it to pets by mixing it with the animal’s food, and vets recommend a course of two to three weeks to clear an infection.
It is not recommended for treating cancer in dogs, although some studies and anecdotal evidence suggest it may also help to clear the disease in the animals.
In animals, the drug works by disrupting cell division in parasites by attacking the microtubules — or the tubes that pull a cell nucleus apart to lead to cell division.
Some researchers have suggested that this may also happen in human cancer cells when someone takes the drug, helping to slow or halt the disease’s progression.
Dr John Campbell, based in the UK, posted online about the drug fenbendazole and called for more research into the treatment
The above graphic shows the microtubules (red lines) that pull apart a nucleus in a cell allowing it to divide into two. Fenbendazole is said to disrupt the microtubules, stopping cell division in cancer cells
Fenbendazole belongs to the class of medications called benzimidazoles, which is the same group as a human deworming drug called Mebendazole.
This drug has been approved by the FDA for deworming use in humans and is available over-the-counter and via prescription as a chewable tablet.
It was previously sold as Vermox, available for about $2 per pill, but is now sold under the brand name Emverm for about $53 per pill without insurance.
Despite its price increase, it costs significantly less than traditional cancer treatments, which run into the tens of thousands.
Side effects may include stomach pain and discomfort, such as bloating and gas, and diarrhea – far less severe than the hair loss, fatigue, vomiting, ulcers and infertility that result from chemotherapy.
Mebendazole has been tested as a cancer treatment in clinical trials where it had some success, including in a 2022 study on patients with advanced colon cancer where it prolonged patients’ lifespans compared to those not taking the drug.
And in lab studies that suggested it could be effective against breast cancer and brain cancer.
Other studies have raised concerns over the drug, however, including a 2021 clinical trial involving 10 patients with advanced liver or colon cancer who were given mebendazole twice a day. After eight weeks, treatment was discontinued because of cancer progression.
In five cases, patients had ‘hyperprogression.’
Scientists at the Williams Institute in California say they do prescribe mebendazole to patients in some circumstances. In a video, a doctor at the Institute said: ‘Menbendazole, taken for what it’s worth, is an FDA approved drug. Fenbendazole is not.’
Studies on fenbendazole have so far only considered case studies on using the drug and lab studies, but have not considered a scientific review.
The above shows the cancerous pancreas of mice before (left) and after (right) they were treated with mebendazole, which is an anti-parasitic agent approved for use in humans
Cases include an 83-year-old man with stage four lymphoma, blood cancer, who took up to six pills a day for a year. Evidence showed the patient’s cancer improved over this time and did not spread.
In another case, a 63-year-old man with advanced renal cell carcinoma started to take fenbendazole three days per week after standard treatments caused severe side effects. Scans later showed the tumor in his left kidney had nearly completely disappeared, while a tumor on his pancreas also shrunk.
Doctors have suggested that these, as well as other cases, may be because of fenbendazole — but they stress they are also anecdotal and patients are simultaneously taking other standard treatments, which may be behind the change.
Using fenbendazole to treat cancer was first popularized by Joe Tippens from Oklahoma, who took the drug once a day for three consecutive days to fight his lung cancer.
He credited the drug with causing the disease to subside, but at the same time he was also on a clinical trial for the immunotherapy drug Keytruda — which is approved for fighting lung cancer.
His claims went viral in South Korea and were shared by local singer Kim Chul-min — who was also battling lung cancer.
Veterinarians at the time reported they were being inundated with phone calls from people seeking doses of the drug.
The country’s ministry of Food and Drug Safety warned at the time: ‘High doses of the drug administered over a long period can cause serious damage to blood, nerves and liver.’
The Korean Medical Association also cautioned: ‘We can’t recommend the use of the drug as no clinical trials have been conducted on humans and its safety has not been confirmed.’
To be approved for use in humans, fenbendazole would have to go through at least three costly clinical trials.
The above video, posted to TikTok, suggested some people may take fenbendazole – which is available as a powder – by mixing it with olive oil
The results would then need to be evaluated by the FDA before the drug could be approved for use in humans to treat cancer.
The process would likely take years and cost in excess of $30million.
Caroline Geraghty, a specialist cancer information nurse at Cancer Research UK, told DailyMail.com: ‘There is insufficient evidence that fenbendazole can cure cancer.
‘The drug has not gone through any clinical trials to find out if it is a safe or effective treatment.’
She added: ‘Unsubstantiated claims that fenbendazole can cure cancer are misleading and can cause harm.
‘Cancer patients should treat any information promoting unconventional treatments online with caution, and always discuss with their doctor before considering new therapies.’
Resurfacing claims about the drug on YouTube, Dr Campbell said: ‘Of course the researchers and the writers here say further research is necessary… we always need more details.
‘But there you go three patients basically, basically… cured of their cancers. Read the paper for yourself, that’s what they seem to be saying to me.’
Regardless, people continue to post online about the anti-cancer benefits of fenbendazole.
One user said on X: ‘A good friend of mine was diagnosed with incurable, terminal cancer, and given less than six months to live.
‘I convinced him to start taking fenbendazole and apricot seeds. He was diagnosed over a year ago and is cancer free now.’
Another user said: ‘It absolutely cured my prostate cancer. The cancer had grown outside the wall. They were giving me a death sentence. I took fenbendazol. Cancer gone.’
And a third said on YouTube: ‘Fenbendazole cured my dog of “terminal” squamous cell carcinoma. Fantastic stuff!
‘My dog had two months to live, I gave her fenben, and 2.5 years later she’s fine!’
