Followers of IMA will know that repurposed drugs like ivermectin and fenbendazole are part of our ever-expanding cancer treatment guidance. Now, that guidance is under pressure from the largest oncology society in America.
In June 2026, the American Society of Clinical Oncology published a clinical notice recommending against the use of ivermectin and fenbendazole for cancer treatment outside of clinical trials. ASCO’s message to oncologists: patients are finding these drugs through social media, and that is a safety problem.
IMA’s Chief Scientific Officer Dr. Paul Marik sees it differently. In a detailed response on Substack, he argues that ASCO is overlooking the evidence that does exist and holding these drugs to a standard that only well-funded pharmaceutical products can realistically meet.
This is not an argument for patients to self-prescribe or replace standard oncology care. It is an argument about which kinds of evidence count, and who gets to decide.
What ASCO Said — and What It Leaves Out
ASCO’s notice states that there is “no robust, peer-reviewed clinical evidence” that these agents are safe or effective for any human cancer, and that well-designed clinical trials are needed. It points to just one in-progress trial and one planned trial.
What the notice does not address, according to Dr. Marik, is everything else: the preclinical research, the mechanistic studies, the pharmacologic data, the observational clinical experience, and the growing body of real-world outcomes. ASCO focused on what is absent. It did not engage with what is present.
Dr. Marik identifies three reasons the standard ASCO is demanding does not fit these therapies:
- Cost: A phase III oncology randomized controlled trial (RCT) can cost hundreds of millions of dollars. For patented drugs that generate billions in revenue, that investment makes sense. For cheap generics and nutraceuticals, there is often no one willing to fund it. The absence of trials is not proof that the drugs do not work.
- Complexity: Cancer protocols built from repurposed drugs may use five, ten, or fifteen agents at once, each targeting a different pathway. Testing every combination in separate RCTs is logistically impossible.
- Real-world mismatch: RCT patients are carefully selected. Many real-world cancer patients are older, sicker, and managing multiple conditions. The patients actually using repurposed drugs are the ones least likely to qualify for the trials being demanded.
Marik points to efforts like the Care Oncology Clinic’s METRICS study as a more realistic model: track structured outcomes from patients on a defined protocol and compare survival against expected benchmarks.
“Demanding a large RCT before even considering low-cost therapies may sound scientific, but it can function as a gatekeeping strategy.” — Dr. Paul Marik
A Better Way to Study These Drugs
The alternative Dr. Marik proposes is not weaker evidence. It is different evidence: track real patients, document outcomes carefully, compare results against matched populations, and replicate independently. Studies in the New England Journal of Medicine and a Cochrane review have shown that well-designed observational studies can produce results comparable to randomized trials.
If you were with IMA during COVID, this will feel familiar. Inexpensive repurposed drugs dismissed not because the science was settled, but because they didn’t fit the system. That fight is now playing out in cancer care.
“The goal should not be to lower scientific standards. The goal should be to use the right standard for the right question.” — Dr. Paul Marik
Dr. Marik’s argument is ultimately about clinician freedom: the ability to consider all reasonable options for individual patients, especially adjunctive therapies supported by biology, clinical experience, and real-world outcomes.
The question is whether medicine is willing to consider the full spectrum of credible evidence when caring for individual patients. At IMA, we believe scientific rigor and clinical judgment should complement one another, not compete. Patients deserve physicians who can thoughtfully evaluate every reasonable option in pursuit of the best possible outcome.
Related Reading
- Hub: Cancer Resource Hub
- Video: Cancer Care: Preventing Cancer — The ROOT Protocols
- Guide: The Approach to Repurposed Drugs for Cancer
- Monograph: Cancer Care: Repurposed Drugs & Metabolic Interventions
- Post: Why Randomized Controlled Trials Are Poorly Suited to Testing Repurposed Drugs and Nutraceuticals in Cancer (Dr. Marik’s full Substack response)
