Prescriptions for an antiparasitic drug spiked for cancer patients after a celebrity endorsed the medication during a recent episode of Joe Rogan’s podcast.

Ivermectin–benzimidazole, a combination of antiparasitic medications, was touted as an off-label cancer treatment during actor Mel Gibson’s January 2025 appearance.

Gibson spoke about three of his friends who had stage 4 cancer, noting that “all three of them don’t have cancer right now at all.” When Rogan asked what treatments they used, Gibson replied, “Ivermectin, fenbendazole.”

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Ivermectin is an antiparasitic medication used in humans and animals to treat infections caused by certain worms and parasites.

Fenbendazoleis, a veterinary antiparasitic drug used to treat worms in animals, belongs to the benzimidazole class of medications, according to medical sources.

“I don’t believe that there is anything that can afflict mankind that hasn’t got a natural cure for it,” Gibson added.

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Researchers from the Virginia Tech Carilion School of Medicine, UCLA and the University of Michigan analyzed the health records of over 68 million patients in ambulatory care settings. 

They checked for increases in same-day prescribing of ivermectin plus a benzimidazole: albendazole, fenbendazole, mebendazole or thiabendazole – with the goal of determining whether Gibson’s endorsement resulted in a spike.

Following the episode, which was viewed 60 million times in the month after airing, overall prescribing rates nearly doubled, rising 2.5 times among cancer patients.

Among those patients, larger increases were seen in men, White patients, people ages 18-64 and those who lived in southern states, the researchers found.

The study, which was published in JAMA Network Open on Tuesday, did not measure any safety outcomes of the drug combination.

No clinical trials have supported the safety or effectiveness of ivermectin–benzimidazole for treating cancer, experts noted.

“Clinicians talk about how difficult it is when the patient demands or asks for a medication that they really feel passionately might help,” said lead author Michelle Rockwell, PhD, RD, a health services researcher at Virginia Tech, in a press release. “And that’s where I think these celebrity influencers really play a big role.”

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While some laboratory and animal studies have shown that these drugs can promote anti-cancer activity, the required dose for even a small effect would “typically be considered toxic for humans,” according to Skyler B. Johnson, MD, of the University of Utah Huntsman Cancer Institute.

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Johnson, who was not involved in the research, shared with CIDRAP News his concerns about ivermectin’s effect on how the body processes cancer treatments and other medications.

The study did have some limitations, including that it was observational in design and could not prove that Gibson’s appearance led to the increase in prescriptions. Also, the fact that prescriptions were ordered does not necessarily mean that they were filled or used.

It is also possible that some patients sought out ivermectin without a prescription, perhaps from agricultural retailers who sell it for livestock.

There is also the potential that cancer status was misclassified, the researchers noted.

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The study also did not assess whether patients were taking ivermectin alongside conventional treatment or if they used it as a substitute.

Patients should consult a qualified healthcare professional for medical guidance before making treatment decisions, doctors say.