Since Hollywood star Mel Gibson said his friends’ cancers had been reversed by the dewormer ivermectin, social media has gone into a frenzy. But is there any evidence that it can work? Bryan Hubbard reports
What have parasites got to do with cancer? If you read Facebook, Instagram and X posts, you’d think quite a lot: For one, the antiparasitic drug ivermectin is being touted as a cancer treatment, and some parasites have been discovered to start cancer, while others have been harnessed to slow the spread of tumors.
Ivermectin, an antiparasitic that treats worm infections, crashed into the public consciousness as a possible cancer therapy last year when Hollywood star Mel Gibson announced to the 11 million listeners to the Joe Rogan podcast that several friends had seen their cancer reverse after taking the drug.
It was also touted as an effective therapy to combat the SARs-CoV-2 virus responsible for the Covid-19 epidemic five years ago. However, it was never tested by a mainstream that was instead waiting for a vaccine to be developed.
The idea that ivermectin could treat cancer isn’t new. Scientists have been investigating its cancer-fighting qualities for more than 30 years.
Although the drug was approved in 1987 to treat worm and parasite infections in people, researchers have been finding that the broad-spectrum antiparasitic can interfere with the internal communication systems of malignant cells. Laboratory tests appear to prove the theory.
One study, published in the influential journal Nature, discovered that when it was used to augment an antibody therapy, the drug caused cell death in a line of breast cancer cells and even targeted those that were causing the tumor to spread. The researchers, from Beckman Research Institute in California, found that ivermectin was affecting secondary tumors as well.1
Parasites can also cause—and treat—cancer. Chronic infection from worms (helminths) can start the cancer cycle by causing inflammation and tissue damage, and organisms like Schistosoma haematobium and liver flukes are recognized carcinogens. Conversely, some parasite-derived molecules are being harnessed to modulate immune responses to tumors.
But the focus of late has been on ivermectin, and yet, say skeptics, research has never stepped beyond the test tube to demonstrate that it can work in cancer patients. That is, until now. A new review has tested the effectiveness of ivermectin—taken with mebendazole, another antiparasitic that treats intestinal infections with threadworms, roundworms and hookworms—on 197 cancer patients.2
The patients, with an average age of 67 and a variety of different cancers, were given one or two capsules daily, containing 25 mg ivermectin and 250 mg mebendazole each, for six months. Before starting the ivermectin treatment, 37 percent had aggressive cancers that were spreading, and 20 percent had been fighting cancer for over five years.
A research team from the McCullough Foundation in Dallas, Texas, reported an overall clinical benefit ratio of 84 percent; in other words, the vast majority saw some noticeable benefit. Nearly half saw their cancer regress, and some even reported that their symptoms had completely disappeared. The disease stabilized in more than 30 percent of the patients, and it worsened in around 16 percent.
The study hasn’t been peer reviewed or published, and an earlier study by the foundation that looked at the effects of ivermectin on Covid-19 patients was withdrawn by the medical journal, Future Microbiology. The new study also relies on patients reporting their own progress.
But the lead investigator, Nicolas Hulscher, believes his team has nonetheless established that ivermectin is worthy of serious consideration as a cancer therapy. He points out that their study isn’t the first to demonstrate the effectiveness of ivermectin in people.
A study in China reported significant effects of ivermectin on glioblastoma, a type of brain tumor that resists other therapies.3 A small randomized controlled trial found that combining mebendazole with Avastin (bevacizumab), a drug for advanced colorectal cancer, and FOLFOX4 chemotherapy in patients with metastatic colorectal cancer dramatically improved response rates from 10 percent to 65 percent while increasing life expectancy from three to nine months.4
A 2025 case series reported complete or near-complete remission in three patients with advanced cancers (breast, prostate and melanoma) who self-administered fenbendazole, an antiparasitic to treat worm infection, and achieved dramatic tumor regression and remission of up to three years without chemotherapy.5
Mainstream medicine has started to put a toe into ivermectin waters. Although America’s drug regulator the Food and Drug Administration (FDA) is opposed to off-label use of ivermectin as a cancer therapy, the US National Cancer Institute (NCI) announced this year that it will carry out preclinical trials with cancer patients. NCI Director Anthony Letai launched the initiative to bridge the chasm between “intense public interest” and reliable studies.
But NCI researchers, perhaps not such avid readers of social media, have questioned the move, arguing that other non-chemo therapies are more deserving of research. Countering the criticism, Letai has said that ivermectin “is not going to be a cure-all for cancer.”
Perhaps not, but it could help, and Chinese researchers think they know why. A research team from Bengbu Medical College in Anhui Province have discovered that it has “powerful antitumor effects, including the inhibition of proliferation, metastasis and angiogenic activity” for a variety of cancers. It interferes with the tumor’s signaling pathways by interacting with PAK1 kinase, a protein that keeps cells alive.
Ivermectin also promotes apoptosis, the immune system’s messaging system that tells damaged cells to die. And it inhibits tumor stem cell development while supercharging the effectiveness of standard cancer therapies.6
The idea that parasites cause cancer was championed in the 1990s by Canadian naturopath Hulda Clark. She was a controversial figure who claimed that parasites were the cause of all cancers; she called out the flatworm, or giant intestinal fluke, Fasciolopsis buski, as the culprit.
Her unorthodox ideas—outlined in her book The Cure for all Cancers (ProMotion Publishing, 1993)—attracted plenty of criticism. For one, the fluke is found exclusively in Asia, so how could that explain the high number of cancer cases in the West?
The Swiss Study Group for Complementary and Alternative Methods in Cancer (SCAC) warned cancer patients to steer clear of Clark and her antidotes. “There is no scientific basis for Hulda Clark’s hypotheses and recommendations, including her suggested treatments. As a whole, Clark’s thesis cannot be comprehended, nor is it proven.”
Prominent alternative medicine proponent Andrew Weil followed suit, warning that “no studies have backed up her bizarre claims, and it’s unclear whether the cancer patients she’s supposedly cured ever had cancer to begin with.”
Clark didn’t help her case by dying from cancer in 2009, and although she may have overplayed her hand—while promoting her own zapper as the cure—researchers have discovered that she was onto something.
The blood fluke (S. haematobium) causes chronic bladder inflammation, leading to squamous cell carcinoma of the bladder, while liver flukes (Opisthorchis viverrini) have been linked to bile duct cancers. A US Centers for Disease Control and Prevention study discovered in 2015 that the dwarf tapeworm (Hymenolepis nana) can become malignant and cause tumors in immunosuppressed people.
Parasite infection causes persistent tissue damage and cellular turnover, promoting mutations, and parasite eggs can act directly as carcinogens. Parasites also interfere with the immune system and can suppress its natural ability to combat cancerous cells.
But when parasites trigger cancer, it usually happens in poor areas. Parasite-related cancer risk is often linked to chronic, untreated infections in regions where healthcare is inaccessible, and the remedy is often as simple as improved sanitation; early treatment of parasitic infections can prevent these cancers.
But where there’s a disease, there’s often also the remedy. The field of onco-parasitology is exploring whether helminth-derived molecules can be used for novel anticancer treatments.
Helminths, or parasitic worms, could trigger the immune system to fight tumors just as they have evolved to modulate our response for their own survival. Helminth antigens can shift the immune environment from pro-tumorigenic to anti-tumorigenic, sometimes activating CD8+ T cells or natural killer cells to attack tumors.
Early tests are looking at harnessing antigens from two helminths, Echinococcus granulosus and Taenia crassiceps, which have shown the ability to inhibit tumor growth and reduce metastasis in animal models of breast and colorectal cancer. Common anthelmintic drugs like mebendazole are being investigated for their ability to disrupt microtubule formation in cancer cells, similar to how they kill parasitic worms.
Despite these promising signals, critics argue that the interest in ivermectin is driven more by social media than by science. Its anticancer abilities have rarely been proven beyond the laboratory test tube, and any human trials have been far too small—although the McCullough study appears to answer that point.
Ivermectin advocates also downplay the dangers: High off-label doses can cause brain swelling, seizures and liver damage, the critics say, and the positive effects seen in the lab have been achieved only with very high doses.
But as we’ve developed very little that successfully combats cancer, other than in its earliest stages, we should be exploring anything that shows promise. When it comes to cancer therapy, the worm must indeed turn.
Ivermectin is a Nobel Prize–winning “wonder drug” discovered in the late 1970s that started life as a veterinary antihelmintic (dewormer) in 1981. Approved for human use in 1987, it became a cornerstone for treating onchocerciasis (river blindness) and other parasitic infections.
Its origins began in 1974 with soil samples taken near a golf course in Kawana, Japan, which microbiologist Satoshi Ōmura tested to isolate the bacterium Streptomyces avermitilis.
Researchers at Merck identified that avermectins, components of the bacteria, had powerful antiparasitic effects in animals. In 1981, ivermectin was launched as Ivomec, a successful dewormer for livestock and pets. Just six years later, it was approved for human use to combat Onchocerca volvulus, the parasite that causes river blindness.
The two men behind ivermectin—Ōmura and Merck’s William C. Campbell—were awarded the Nobel Prize in Physiology or Medicine in 2015.
What do you think? Start a conversation over on the... WDDTY Community
Great news! Discounts are available based on your cart total. Check the details below:
