Old Drugs, New Questions: What to Know About Repurposed Medications for Cancer and Beyond

By Shawn Rowland, MD

If you have spent any time in online health communities lately, you have probably run into the idea that a handful of old, cheap, widely available medications might do more than we realized. Ivermectin and mebendazole, drugs most people associate with deworming a dog or treating a child's pinworms, are being discussed as possible tools against cancer. Hydroxychloroquine, metformin, and a veterinary cousin of mebendazole called fenbendazole come up in the same conversations.

I want to walk through this topic the way I would with a patient or a friend: taking it seriously, being honest about what we actually know, and being equally honest about where the science is still young. My goal here is not to tell you what to do. It is to help you understand the landscape so that you can ask better questions and make informed decisions with a clinician you trust.

What "drug repurposing" actually means

Drug repurposing simply means using an existing, approved medication for a condition it was not originally designed to treat. This is not fringe science. Aspirin started as a pain reliever and is now taken by millions for heart health. Minoxidil was a blood pressure drug before it became a hair-loss treatment. Thalidomide, infamous for tragedy, found redemption as a treatment for multiple myeloma.

The appeal in oncology is straightforward. New cancer drugs take more than a decade and often more than a billion dollars to develop. Older generic drugs already have decades of human safety data and cost pennies. As the peer-reviewed Repurposing Drugs in Oncology (ReDO) Project put it, repurposing can be seen "as a response to the declining productivity of oncological drug development, as a strategy to reduce development times, and as a source of low-cost treatments to meet the increased demands and unmet needs of cancer patients."

There is a catch, and the same academic group named it plainly. A new patented drug arrives with a built-in army of advocates funded by its manufacturer. A cheap generic does not. "For repurposed drugs," the ReDO authors wrote, "this pool of advocates is largely missing." Economists have a term for this: the "financial orphan." A drug can be promising and still go untested simply because no company stands to profit from running the expensive trials. That gap, more than anything, is why this conversation has moved to podcasts and Substacks instead of journal pages, and it is worth understanding before we go further.

The people driving the conversation

A relatively small group of physicians and patients has pushed repurposed medications into public view. It is worth knowing who they are and what they actually claim.

Joe Tippens is the patient whose story launched much of the current interest. Diagnosed with widely metastatic small-cell lung cancer and given a few months to live, he began taking fenbendazole on a veterinarian's tip and later reported a complete scan. In his own words, "I had late stage small cell lung cancer that had metastasized throughout my entire body and was told I only had a few months to live. From there, I found an unlikely pathway to 'get busy living' instead of 'get busy dying.'" To his credit, Tippens is upfront about his limits. His blog opens with a disclaimer in capital letters: "I AM NOT A DOCTOR OR A SCIENTIST, BUT SIMPLY SOMEONE WHO HAS A VERY UNUSUAL STORY TO TELL." It is also worth noting he was enrolled in an experimental immunotherapy trial at the same time, a detail that makes his case harder to interpret, not less interesting.

Dr. Kathleen Ruddy, a breast surgeon, has become one of the more visible clinical voices. "I was as astonished as anyone that simple ivermectin has great potential as an anti-cancer agent," she has said. She frames the safety case bluntly: "Ivermectin is safer than a sugar pill. You'd have to take a lot to make yourself sick." That is a striking claim, and while ivermectin does have a wide safety margin at standard doses, "safer than a sugar pill" is rhetoric, not a pharmacology statement. I will come back to the safety nuances, because they matter.

Dr. William Makis, a Canadian physician, publishes a steady stream of patient testimonials pairing ivermectin, fenbendazole, and mebendazole. A typical post reads: "IVERMECTIN and FENBENDAZOLE Testimonial - 56 year old Canadian man with Stage 4 Pancreatic Cancer reports after 6 months: dramatic tumor shrinkage." These are compelling to read. They are also, by their nature, anecdotes: self-selected, uncontrolled, and usually impossible to verify independently.

Dr. Paul Marik and the Front Line COVID-19 Critical Care Alliance (FLCCC) brought a more structured, protocol-driven approach. Marik's view, laid out in his free book Cancer Care: The Role of Repurposed Drugs and Metabolic Interventions in Treating Cancer, is that cancer should be understood less as a purely genetic disease and more as a disorder of cellular metabolism, and that drugs like metformin, mebendazole, and ivermectin are worth using for their metabolic effects rather than their original purpose. The FLCCC protocol organizes these agents into tiers and is the closest thing this movement has to a written, citable framework.

Dr. Justus Hope, who writes under a pen name, is perhaps the most enthusiastic. "We are witnessing the greatest transformation in cancer medicine since the discovery of chemotherapy," he has written. It is a bold framing. Bold framing is not evidence, but it captures the conviction driving this community.

What the science actually shows

Here is where honesty matters most, because the evidence is not all one thing. It runs along a spectrum, and knowing where a given claim sits on that spectrum is the single most useful skill you can bring to this topic.

At one end are laboratory and animal studies. There is a genuine and growing body of this work. Ivermectin has been shown in cell and animal studies to interfere with several pathways cancer cells rely on. Mebendazole disrupts the internal scaffolding that cells need to divide. These findings are real and they are why serious researchers find the topic interesting. But a result in a petri dish or a mouse is a starting point, not a finish line. The history of cancer research is full of compounds that dazzled in the lab and disappointed in people.

In the middle are case reports and testimonials, the Tippens and Makis stories. These can generate hypotheses and they can offer hope, but they cannot tell us how often something works, in whom, or whether the drug was even responsible. People who recover tell their stories; the data from those who did not are rarely collected.

At the stronger end are actual human clinical trials, and this is where I would point anyone who wants the most solid footing. Mebendazole has gone through early-phase trials in brain cancer at Johns Hopkins. Among the wider repurposing field, some agents have surprisingly good human data: cimetidine, an old heartburn drug, was associated with markedly better survival in a subset of colorectal cancer patients in a controlled trial, and itraconazole, an antifungal, showed a meaningful survival signal in a lung cancer study. These are the kinds of findings that deserve real attention precisely because they come from controlled human research rather than testimonials.

So when someone tells you "ivermectin cures cancer," the accurate response is more careful: there are plausible mechanisms, encouraging laboratory work, a collection of anecdotes, and early human research, but we do not yet have the large controlled trials that would let anyone honestly use the word "cure." That is not a dismissal. It is simply where the evidence stands today.

The part that is not in doubt: these are proven, safe medicines for other uses

One reason these drugs are even in the conversation is that we know them extremely well, and it is worth remembering what they are unambiguously good at.

Ivermectin is FDA-approved and highly effective for parasitic infections like strongyloidiasis and river blindness, and it is a mainstay, used off-label, for scabies and stubborn head lice. In a topical cream it is approved for rosacea. Mebendazole is a frontline treatment for the common intestinal worms, pinworm, roundworm, hookworm, and whipworm, and a single short course is among the safest interventions in all of medicine. These are not exotic claims. They are decades of established practice, and they are the foundation for the reasonable observation that these drugs are, at appropriate doses, generally well tolerated.

That track record is genuine, and it is part of why the cancer question is worth asking at all. But "safe as an occasional dewormer" and "safe at high doses, taken daily, for months, alongside other drugs" are different statements, and conflating them is where people get into trouble.

Where caution genuinely matters

I am all for patients being curious and engaged. I am also a physician, and there are real considerations I would not want anyone to skip.

Dose and duration change the risk picture. The cancer protocols use far higher doses, taken far longer, than any antiparasitic use. Fenbendazole, the veterinary drug in the Tippens protocol, has documented cases of liver injury in people using it for cancer. Mebendazole's rare serious effects show up almost exclusively at high, prolonged doses. Hydroxychloroquine can affect the eyes and heart. None of this means these drugs are dangerous in the way that word usually implies, but it does mean monitoring, periodic bloodwork especially for the liver, matters.

Interactions are easy to overlook. Ivermectin can increase the effect of the blood thinner warfarin. It interacts with certain antifungals and heart medications in ways that can raise the amount reaching the brain. These are manageable, but only if someone is actually managing them.

And the most important point of all: please do not abandon conventional treatment based on a testimonial. The most heartbreaking situations I can imagine are the ones where someone with a treatable cancer turns away from proven therapy in favor of an unproven one. Many of the physicians in this space are explicit that they see repurposed drugs as a complement to standard care, not a replacement for it. That is the right framing.

How to approach this wisely

If this topic interests you or someone you love, here is what I would suggest. Bring it to your oncologist or physician rather than going it alone, and bring specifics, the actual drugs, doses, and any studies you have found, so the conversation can be concrete. A good clinician would rather discuss this openly than have you do it in secret. Ask about monitoring and interactions with your current medications. And calibrate your expectations to the evidence: be most confident about these drugs' approved uses, genuinely interested in the early cancer research, and appropriately skeptical of anyone promising certainty.

The story of repurposed medications is, at its heart, a story about good questions that our system is poorly designed to answer, because no one profits from answering them. That is a legitimate frustration, and it is why so many people feel they have to figure this out themselves. My hope is that better information helps you do that more safely, and in partnership with someone qualified to help.

Appendix: Examples of published protocols

Because people always ask "but what do these actually look like," here are several of the most-cited protocols, reproduced as their authors have published them. I want to be very clear about why I am including these and how to read them. These are not my recommendations, and they are not a menu to order from. They are documented examples, with real doses, so you can see what proponents are actually describing and bring something concrete to a conversation with your physician. The doses are higher and the durations longer than any approved use of these drugs, several of these agents can affect the liver, and they carry drug interactions, so monitoring and medical supervision are not optional. Published versions also vary and get updated, so treat these as snapshots.

The Joe Tippens Protocol (the original patient-popularized regimen)

• Fenbendazole 222 mg per day, commonly taken 3 days on, 4 days off
• Vitamin E (around 800 IU per day, often paused on fenbendazole days in some versions)
• Bio-available (nano) curcumin, around 600 mg per day
• CBD oil

FLCCC / Dr. Paul Marik "Cancer Care" Protocol (a fixed-dose, tiered framework; agents are organized by evidence tier in the full book)

• Ivermectin 12 to 18 mg per day (roughly 1 mg/kg), taken with food
• Mebendazole 100 to 200 mg per day
• Vitamin D3 20,000 to 50,000 IU per day, dosed to a target blood level
• Metformin 1,000 mg twice daily
• Atorvastatin 40 mg twice daily
• Melatonin 20 to 40 mg at night, plus curcumin, omega-3, green tea catechins, and berberine
• The full protocol and its rationale are in Marik's free book, Cancer Care: The Role of Repurposed Drugs and Metabolic Interventions in Treating Cancer (FLCCC / IMA Health)

Dr. William Makis weight-based approach (doses scaled to body weight and stratified by how aggressive the cancer is)

• Ivermectin from 0.5 mg/kg three times weekly for lower-grade situations up to 1 to 2.5 mg/kg daily for aggressive disease, taken with a fatty meal
• Fenbendazole from 222 mg three times weekly up to around 1,000 mg per day
• Mebendazole from 200 mg up to 1,500 mg per day
• Supportive agents he describes include vitamin D3, intravenous vitamin C, curcumin, and berberine, with liver-function monitoring on a regular schedule

The Care Oncology Clinic ("COC") metabolic protocol (a more conventional-adjacent, clinic-administered four-drug regimen studied as an add-on to standard care)

• Atorvastatin 40 to 80 mg per day
• Metformin 500 mg, increased to twice daily
• Doxycycline 100 mg per day
• Mebendazole 100 mg per day

A few honest notes on these. The Tippens regimen centers on fenbendazole, a veterinary drug not approved for human use, which is the version most associated with reported liver injury. The two FLCCC dosing schemes that circulate (the fixed doses in the Cancer Care book versus a weight-based version in a separate publication) are not identical, so people sometimes conflate them. And the Care Oncology protocol, notably, was generally used alongside standard oncology care rather than instead of it, which is the spirit in which most clinicians in this space intend all of this.

---

This article is for general educational purposes and is not medical advice. The medications discussed are not FDA-approved to treat cancer, and the cancer-related uses described here are unproven and experimental. Nothing here should be used to diagnose or treat any condition or to make decisions about your care without consulting a qualified, licensed healthcare professional. Do not start, stop, or change any treatment based on this article, and never discontinue recommended cancer therapy without speaking to your oncologist.