Prescriptions for the anti-parasite medication ivermectin doubled in the months following an endorsement by a celebrity during a high-profile podcast as an off-label cancer treatment, a UCLA-led study finds.
The endorsement came on January 9, 2025, when actor Mel Gibson appeared on The Joe Rogan Experience and described three friends with stage IV cancer who he said recovered after taking ivermectin and fenbendazole. Clips of the segment were viewed tens of millions of times across social media in the weeks that followed.
Although ivermectin and benzimidazole drugs like fenbendazole have shown anti-cancer activity in laboratory cells and animal studies, no clinical trials have shown they are safe or effective for treating cancer in people. Ivermectin is FDA-approved for parasitic infections in humans; fenbendazole is approved only for veterinary use.
The increases were largest among men, White patients, residents in the US south, and people with cancer.
The findings, published May 12 in the peer-reviewed journal JAMA Network Open, raise concerns that celebrity endorsements like this could influence people to turn to unproven treatments, at the risk of delaying or forgoing conventional treatments that have been confirmed to work.
“As a primary care doctor, I want my patients and people across the country to have the chance to get treatments we know can help them live longer, healthier lives," said senior author Dr. John N. Mafi, an associate professor-in-residence of medicine, division of general internal medicine and health services research at the David Geffen School of Medicine at UCLA. “When prescribing for an unproven cancer treatment more than doubles after a single podcast, especially among men and people in the South, it raises a concern that patients may be skipping or delaying treatments we know work in favor of something that hasn't been proven to help them.”
The researchers compared prescription patterns for the combination ivermectin-benzimidazole among people with and without cancer from January 1 through July 31, 2025 following the endorsement to prescription patterns for the medication combination from the corresponding year-ago period. They used de-identified electronic health records from more than 68 million patients from the multicenter US TriNetX research network capturing prescriptions given to 18- to 90-year-old patients in ambulatory care and emergency departments.
They found that overall prescribing rates within the entire cohort doubled during the months following the endorsement compared with the similar year-ago period. Among people with cancer, prescribing rates were more than 2.5 times higher during the more recent period. In the US South, those rates were more than three times higher during the six months in 2025 compared with the same period the previous year.
“We often focus on how to efficiently get evidence into practice,” said Dr. Michelle Rockwell, an assistant professor of family and community medicine at Virginia Tech and the study’s lead author. ”But these findings remind us that some forces can influence care very quickly. The challenge for health systems is how to meet patients in that moment with information that is both timely and trustworthy.”
The study has some limitations. The study’s observational design cannot establish cause and effect. Given that it was a convenience sample, it may not be representative of the entire US. Also, it focused on physician orders rather than actual use of the drug.
The findings raise several questions that warrant further study: whether patients are substituting ivermectin-benzimidazole for proven cancer treatments, whether its use leads to adverse outcomes, which physicians are prescribing it and in what settings, and what strategies can counter misinformation at the point of care.
“Not all widely shared health information is accurate, even when it comes from familiar or influential sources,” said co-author Dr. Katherine Kahn, Distinguished Professor of Medicine at the Geffen School and member of the UCLA Health Jonsson Comprehensive Cancer Center. “Using unproven treatments can carry real risks, especially if it delays care that is known to work. Clinicians and health systems play a critical role in helping patients navigate information and make informed decisions.”
Study co-authors are Sitaram Vangala of UCLA and Dr. A Mark Fendrick of the University of Michigan.
The National Institute on Aging (R01AG070017-01) and an NIA Beeson Emerging Leaders in Aging Research Career Development Award (K76AG064392-01A1) supported this study.
