Cancer Care: Paul Marik's Book on Repurposed Drugs

Paul Ellis Marik is a critical-care physician trained in Johannesburg, South Africa, who led intensive-care divisions in Philadelphia and Norfolk, Virginia, and wrote three editions of an evidence-based critical-care textbook. In 2023 he published a very different book: Cancer Care: The Role of Repurposed Drugs and Metabolic Interventions in Treating Cancer.

This page sets out what that book says about repurposed drugs — medicines and supplements already licensed or sold for other purposes — as Marik states it: the book’s editions and stated purpose, the four evidence tiers he uses to rank the agents, which agents he places in each tier, what he writes about ivermectin and mebendazole, his plain statement that cancer is not a parasitic disease, and what later published research has found for several of the agents he ranks highest. The book also gives dose schedules; this page names the agents and the tiers he assigns but leaves the doses out. The diet and lifestyle half of the book has its own page, Paul Marik’s Metabolic Approach to Cancer.

Table of Contents

  1. The Book and Its Two Editions
  2. The Book’s Stated Purpose and Why He Turned to Repurposed Drugs
  3. How Marik Ranks the Evidence in Four Tiers
  4. Tier One: The Agents He Ranks Highest
  5. Tiers Two, Three and Four
  6. Second-Edition Changes and Drug Combinations
  7. Ivermectin in Cancer Care
  8. Mebendazole and Fenbendazole in Cancer Care
  9. Cancer Is Not a Parasitic Disease, in Marik’s Words
  10. Antioxidants, Monitoring and His Later Guides
  11. Later Research on Several Tier One Agents
  12. Key Research Papers
  13. Connections
  14. Featured Videos

1. The Book and Its Two Editions

Cancer Care: The Role of Repurposed Drugs and Metabolic Interventions in Treating Cancer was published by the Front Line COVID-19 Critical Care Alliance (FLCCC), the physicians’ group Marik co-founded in April 2020. The group now calls itself the Independent Medical Alliance (IMA) and describes itself as “formerly FLCCC”.

In the preface Marik writes that he “read more than 1800 peer-reviewed papers” while preparing the book. Alongside it he published a peer-reviewed companion review with Matthew Halma and Jack Tuszynski, “Cancer Metabolism as a Therapeutic Target and Review of Interventions”, in the journal Nutrients in 2023.

He no longer treats patients himself. In the preface he writes: “While I no longer see patients directly, I will forever be bound by my Hippocratic Oath to ‘first do no harm’.”

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2. The Book’s Stated Purpose and Why He Turned to Repurposed Drugs

The book opens with a disclaimer that sets its limits. “This monograph is not intended as a stand-alone guide to treating cancer,” Marik writes. He presents it as a review of the published literature, meant to be used “primarily as adjunctive therapy in addition to the treatment provided by an oncologist” — that is, alongside cancer specialists’ care, not in place of it.

He is equally direct about what the book does not claim: “I want to be clear that I am not suggesting I have found a cure for cancer, nor am I the first to propose using repurposed drugs for cancer.”

On patient choice, he writes that a patient “may decide to forego conventional chemotherapy and radiotherapy” and has the right to make that decision “under the principles of true informed consent”. This is reported here as his stated position on patient autonomy; the same disclaimer frames the book as an addition to a cancer specialist’s treatment.

The case for repurposing

Marik’s argument for repurposing rests on the fact that doctors already use licensed medicines outside their original approval. “Around 30 percent of all prescriptions in the United States are written for off-label uses,” he writes. Repositioning existing licensed drugs, in his view, can offer “safe, affordable, and effective treatments in a short period of time”, because their safety records and manufacturing are already established.

He was not the first to make this argument for cancer. Since 2014 the Repurposing Drugs in Oncology (ReDO) project has published reviews of non-cancer drugs with anticancer evidence, starting with mebendazole and later propranolol, and in 2018 released a public database of candidate drugs. Marik cites that database in the book.

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3. How Marik Ranks the Evidence in Four Tiers

The core of the book’s drug chapter is a ranking. Marik sorts each drug and nutraceutical (a food-derived supplement) into one of four tiers according to what he calls “the totality of evidence” — cell studies, animal studies, observational studies in people and clinical trials taken together. An appendix to the book sets out the method he used.

The words “strong” and “weak recommendation” are Marik’s own grading terms. The sections below say which kind of evidence — cell, animal, observational or trial — applies where the book or later research makes it clear.

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4. Tier One: The Agents He Ranks Highest

In version 2.2 of the second edition, Marik places seventeen agents in Tier One, in this order:

  1. Vitamin D3
  2. Propranolol, a beta-blocker blood-pressure medicine
  3. Melatonin
  4. Metformin, a diabetes medicine
  5. Curcumin, the main active compound of turmeric
  6. Ivermectin, an antiparasitic medicine
  7. Mebendazole, together with the related antiparasitic drugs fenbendazole and albendazole
  8. Green tea catechins
  9. Omega-3 fatty acids
  10. Berberine
  11. Atorvastatin or simvastatin, cholesterol-lowering statins
  12. Sildenafil-type phosphodiesterase-5 (PDE5) inhibitors
  13. Disulfiram, a medicine used in alcohol dependence
  14. Ashwagandha
  15. Itraconazole, an antifungal medicine
  16. Mistletoe
  17. Cimetidine, a stomach-acid medicine

The list mixes prescription medicines (propranolol, metformin, the statins, the phosphodiesterase-5 inhibitors, disulfiram, itraconazole, cimetidine), antiparasitic drugs (ivermectin, mebendazole) and nutraceuticals and plant extracts (vitamin D3, melatonin, curcumin, green tea catechins, omega-3 fatty acids, berberine, ashwagandha, mistletoe). Each prescription medicine on it carries the side effects and drug interactions listed in its own prescribing information; Marik’s ranking does not change those.

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5. Tiers Two, Three and Four

Tier Two — weak recommendation

Tier Three — insufficient data

Tier Four — recommended against

The Tier Four list matters as much as Tier One for understanding the book: Marik does not endorse every alternative cancer remedy in circulation, and several long-promoted ones are among the agents he ranks against.

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6. Second-Edition Changes and Drug Combinations

The second edition reorders the tiers. In his second-edition preface Marik notes that the ranking has changed since the first. Among the changes:

Combinations rather than single agents

Marik writes that “the use of a single repurposed drug/nutraceutical is likely to be ineffective”. He describes the agents as acting additively or synergistically — each adding to, or amplifying, the effect of the others — and also with standard chemotherapy. He favours metronomic chemotherapy, a schedule of lower doses given more frequently, over the conventional pattern of high doses with long breaks.

One multi-drug example he discusses is a four-drug off-label regimen (metformin, atorvastatin, mebendazole, doxycycline) studied in the retrospective METRICS cohort, an observational review of patients’ records rather than a randomized trial.

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7. Ivermectin in Cancer Care

Ivermectin is best known as an antiparasitic medicine; its discoverers, Satoshi Ōmura and William C. Campbell, shared the 2015 Nobel Prize in Physiology or Medicine. Marik opens his ivermectin section with that history and then reviews the anticancer mechanisms reported in the laboratory. These include effects on:

These mechanisms come from cell studies and animal studies. Marik is explicit about the human evidence: “the reported clinical effectiveness is limited to small case series”. He also writes that “the optimal dosing strategy with ivermectin is unclear”, and adds a limit on where it might act: “As ivermectin does not cross the blood-brain barrier, it is likely ineffective for brain tumors.”

Independent reviews describe the same gap between the laboratory and the clinic. A 2021 review in Pharmacological Research catalogued how ivermectin inhibited several kinds of tumour cells by regulating multiple signalling pathways. A 2025 review in Current Oncology Reports found that preclinical studies (cell and animal) show anticancer effects, but that clinical evidence in humans is limited, with no large-scale randomized controlled trials confirming a benefit; it also reported cases of toxicity in cancer patients who took ivermectin on their own. The site’s page Ivermectin in Cancer Studies collects that research. Marik himself states that “There is no evidence that cancer is caused by or related to any parasitic disease” (see section 9).

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8. Mebendazole and Fenbendazole in Cancer Care

Mebendazole is a benzimidazole, a family of worm medicines that also includes albendazole and the veterinary drug fenbendazole. Marik groups the three together in Tier One. He describes mebendazole’s reported anticancer actions as:

On the human evidence he again states the limit plainly: clinical use “is limited to a few case reports … and a small case series”. Mebendazole was also one of the four drugs in the off-label regimen studied in the retrospective METRICS cohort.

What later reviews found

The site’s page Benzimidazoles: Mebendazole and Fenbendazole in Cancer covers this research in more depth. As Marik puts it: “There is no evidence that cancer is caused by or related to any parasitic disease.”

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9. Cancer Is Not a Parasitic Disease, in Marik’s Words

Because two of his Tier One agents are antiparasitic drugs, Marik addresses directly the idea that cancer is a parasite problem. His statement is unambiguous:

“There is no evidence that cancer is caused by or related to any parasitic disease.”

He explains why antiparasitic drugs appear in a cancer book at all: they act on cancer “via specific biochemical pathways specific to the cancer cell which are distinct from their anti-parasitic mechanisms of action.” In other words, in his account ivermectin and mebendazole are of interest because of what they do to cancer-cell machinery — microtubules, growth signalling, stem-cell pathways — not because they kill a hidden parasite.

The site’s Cancer and Parasites section reports research and claims about parasites and about antiparasitic drugs in cancer, including the pages on ivermectin and on mebendazole and fenbendazole. Readers coming from that section will find that Marik, who ranks both drugs in Tier One, states that “There is no evidence that cancer is caused by or related to any parasitic disease.”

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10. Antioxidants, Monitoring and His Later Guides

Oral antioxidant supplements

One of the book’s less expected positions concerns antioxidants. Marik writes that oral antioxidant supplements — vitamins A, C and E, coenzyme Q10 and N-acetylcysteine — “should be avoided in patients with cancer”, especially during chemotherapy and radiotherapy. He contrasts this with high-dose intravenous vitamin C, which he says acts differently by generating reactive oxygen species; he nonetheless places high-dose intravenous vitamin C in Tier Three (insufficient data). This is his stated position in the book, reported as his.

Monitoring

Marik describes following a patient’s response with positron emission tomography (PET) scans every three months, tumour markers in the blood and circulating tumour DNA, and writes of tapering a regimen gradually rather than stopping it abruptly.

Later guides

After the second edition, Marik wrote a series of shorter guides on the Independent Medical Alliance website, among them “The Approach to Repurposed Drugs for Cancer” (with a co-author, first issued in 2025 and last updated in March 2026), “Stopping the 10 Deadliest Cancers”, “Targeting Cancer Stem Cells”, “Perioperative Repurposed Drugs for Cancer” and “Cancer Resistance Mitigation”. The 2025 guide offers a “Limited” and an “Aggressive” approach, explaining that “The goal in both is to block multiple cancer stem cell (CSC) pathways”, and tells readers: “Always discuss these with your physician before starting or adjusting therapy.”

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11. Later Research on Several Tier One Agents

Several of Marik’s Tier One agents have been tested in pooled analyses of human studies. The results below come from the abstracts of those papers and are described as the papers state them. None of them tested Marik’s combinations; each looked at one agent or one drug class.

A hazard ratio or relative risk below 1 means fewer events in the treated group; above 1 means more. Where a result is “not significant”, the study could not distinguish the effect from chance.

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Key Research Papers

  1. Halma MTJ, Tuszynski JA, Marik PE. Cancer Metabolism as a Therapeutic Target and Review of Interventions. Nutrients. 2023;15(19):4245. — PubMed PMID: 37836529
  2. Pantziarka P, Bouche G, Meheus L, Sukhatme V, Sukhatme VP, Vikas P. The Repurposing Drugs in Oncology (ReDO) Project. Ecancermedicalscience. 2014;8:442. — PubMed PMID: 25075216
  3. Pantziarka P, Verbaanderd C, Sukhatme V, Rica Capistrano I, Crispino S, Gyawali B, et al. ReDO_DB: the repurposing drugs in oncology database. Ecancermedicalscience. 2018;12:886. — PubMed PMID: 30679953
  4. Pantziarka P, Bouche G, Sukhatme V, Meheus L, Rooman I, Sukhatme VP. Repurposing Drugs in Oncology (ReDO)-Propranolol as an anti-cancer agent. Ecancermedicalscience. 2016;10:680. — PubMed PMID: 27899953
  5. Pantziarka P, Bouche G, Meheus L, Sukhatme V, Sukhatme VP. Repurposing Drugs in Oncology (ReDO)-mebendazole as an anti-cancer agent. Ecancermedicalscience. 2014;8:443. — PubMed PMID: 25075217
  6. Juarez M, Schcolnik-Cabrera A, Dueñas-Gonzalez A. The multitargeted drug ivermectin: from an antiparasitic agent to a repositioned cancer drug. Am J Cancer Res. 2018;8(2):317-331. — PubMed PMID: 29511601
  7. Tang M, Hu X, Wang Y, Yao X, Zhang W, Yu C, et al. Ivermectin, a potential anticancer drug derived from an antiparasitic drug. Pharmacol Res. 2021;163:105207. — PubMed PMID: 32971268
  8. Patel Y, Chawla J, Parmar MS. Ivermectin in Cancer Treatment: Should Healthcare Providers Caution or Explore Its Therapeutic Potential? Curr Oncol Rep. 2025;27(9):1070-1079. — PubMed PMID: 40715995
  9. Guerini AE, Triggiani L, Maddalo M, Bonù ML, Frassine F, Baiguini A, et al. Mebendazole as a Candidate for Drug Repurposing in Oncology: An Extensive Review of Current Literature. Cancers (Basel). 2019;11(9):1284. — PubMed PMID: 31480477
  10. Chai JY, Jung BK, Hong SJ. Albendazole and Mebendazole as Anti-Parasitic and Anti-Cancer Agents: an Update. Korean J Parasitol. 2021;59(3):189-225. — PubMed PMID: 34218593
  11. Blum CB, McMenamin M, Khoo T, Edwin JM, Jose P, O'Callaghan LA. From anthelmintic to neuro-oncology: A systematic review of mebendazole repurposing for brain tumour therapy. Br J Clin Pharmacol. 2026. — PubMed PMID: 42120351
  12. Nguyen J, Nguyen TQ, Han BO, Hoang BX. Oral Fenbendazole for Cancer Therapy in Humans and Animals. Anticancer Res. 2024;44(9):3725-3735. — PubMed PMID: 39197912
  13. Keum N, Lee DH, Greenwood DC, Manson JE, Giovannucci E. Vitamin D supplementation and total cancer incidence and mortality: a meta-analysis of randomized controlled trials. Ann Oncol. 2019;30(5):733-743. — PubMed PMID: 30796437
  14. Wen J, Yi Z, Chen Y, Huang J, Mao X, Zhang L, et al. Efficacy of metformin therapy in patients with cancer: a meta-analysis of 22 randomised controlled trials. BMC Med. 2022;20(1):402. — PubMed PMID: 36280839
  15. Zhang F, Wang Y, Liu F, Li Y, Liu X, Ren X, et al. Impact of beta blockers on cancer neuroimmunology: a systematic review and meta-analysis of survival outcomes and immune modulation. Front Immunol. 2025;16:1635331. — PubMed PMID: 40842986

PubMed Topic Searches

  1. Drug repurposing in cancer
  2. Ivermectin and cancer
  3. Mebendazole and cancer
  4. Propranolol and cancer survival
  5. Paul Marik’s papers on cancer

Further Reading

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Connections