Repurposed Drugs for Cancer

by | Feb 10, 2023 | Articles, Cancer, Conditions

Many drugs have “pleotropic” properties, meaning they have actions other than those for which the agent was specifically developed.  While the quest for better treatments for cancer is ongoing, there is still a large unmet need and increasing interest in the potential of existing drugs and natural substances for their possible pleotropic role in cancer treatment.

The “repurposing” of old medications comes about given the shortcomings of existing chemotherapy options, the high cost and time input for new drug development, and the need for more tumor specific therapies.  Drugs such as ivermectin, fenbendazole, metformin, doxycycline, and others that have a history of known safety and efficacy for other conditions may prove to be valuable additions to conventional cancer therapies.

Note these drugs are not FDA approved to treat cancer.  There may be only a few, or no clinical trials to date that confirm their safety and efficacy as anticancer drugs for humans.  The information in this article is for education purposes only.


Ivermectin is well known as an incredibly safe and effective drug for treating gastrointestinal parasitic nematodes, lungworms, lice, and mange, but it may also hold potential for treating cancer.  The story of Ivermectin starts with its origin from a soil sample from the south east coast of Honshu, Japan.  In 1970, microbiologist Satoshi Omura collected the soil and isolated an unknown species of Streptomyces bacterium.  He sent the sample to an an Irish biologist and parasitologist named Dr William Campbell who worked at Merck.  Dr Campbell noted the cultures show potent anti-parasitic effects against roundworms and isolated the active compounds.  He gave these compounds the name avermectins due to the “averminous” lack of worms that resulted.  One of the best synthetic derivatives of the naturally occurring avermectins turned out to be Ivermectin.

By the 1980s Ivermectin was being used within the veterinary realm as the largest selling animal health product in the world.  Also during this time another Merck researcher, Dr. Mohammed Aziz, helped develop a program to donate Ivermectin for treating a devastating disease called river blindness that plagued remote communities in Africa and Latin America.  In collaboration with the World Health Organization the drug continues to be distributed to these regions in an effort to completely eliminate river blindness as well as elephantiasis.  In 1987, Merck committed to donate Ivermectin – as much as needed, for as long as needed – with the goal to help eliminate river blindness.  At this time more than 4 billion doses have been given to people in 49 countries.

Satoshi Omura and William Campbell won the 2015 Nobel Prize in Physiology or Medicine for the discovery of the excellent efficacy of ivermectin against parasitic diseases.

Ivermectin as an Anti Cancer Drug

In recent years Ivermectin has been examined for its anticancer potential.  Ivermectin has been shown in laboratory research to be effective against a wide variety of cancers through multiple mechanisms, including:

  • increased programmed cell death through apoptosis, autophagy and pyroptosis
  • influence on multiple molecular targets and signaling pathways
  • Decreasing angiogenesis and metastases
  • Enhancing conventional drug activity and reducing multi-drug resistance

Ivermectin, a potential anticancer drug derived from an antiparasitic drug

“Recently, ivermectin has been reported to inhibit the proliferation of several tumor cells by regulating multiple signaling pathways. This suggests that ivermectin may be an anticancer drug with great potential.”

Ivermectin Could Be a ‘Powerful Drug’ for Fighting Cancer, Here’s Why


Developed by Janssen Pharmaceutica in the 1970s, Fenbendazole, commonly known as Fenben, is a broad spectrum anti-parasitic drug widely used in veterinary medicine for decades.  It is part of the benzimidazole family of drugs, which includes mebendazole and albendazole used in humans.  These drugs have been shown in laboratory reserarch to be toxic to cancer cells via several mechanisms, including:

  • increased cell death through apoptosis and autophagy
  • impairing glucose uptake of cancer cells
  • preventing angiogenesis
  • reducing drug resistance

Teaching an old dog new tricks: The case of Fenbendazole

Fenbendazole acts as a moderate microtubule destabilizing agent and causes cancer cell death by modulating multiple cellular pathways

“The results, in conjunction with our earlier data, suggest that Fenbendazole is a new microtubule interfering agent that displays anti-neoplastic activity and may be evaluated as a potential therapeutic agent because of its effect on multiple cellular pathways leading to effective elimination of cancer cells.”


Metformin is one of the best and most widely used drugs for treating diabetes.  It was a game changer for diabetics as the first drug that helped insulin work better instead of simply increasing insulin levels.

The beneficial effects of metformin on cancer prevention and therapy: a comprehensive review of recent advances

“Therefore, this drug can be used as a complementary therapeutic agent for cancer treatment and prevention.  In this review, we have summarized the data from various experimental and clinical studies and highlight the possible potential effects of metformin on cancer therapeutic responses.”


Doxycycline is one of the tetracycline family of antibiotics first introduced in 1967 by Pfizer.  It was known as one of the earliest broad spectrum antibiotics and is still widely used today against an wide array of gram-positive, gram negative, and “atypical” bacteria, as well as certain protozoa such as malaria.

Doxycycline as Potential Anti-cancer Agent

“In this article, we try to introduce a new concept of cancer pharmacology, by offering new off-label use of Doxycycline, which is characterized by selective toxicity, as potential anticancer agents.”

Doxycycline: new tricks for an old drug

“Taken together, these studies suggest that doxycycline, a drug that has been utilized for over 50 years as an antimicrobial agent and more recently in dermatological conditions, could also have efficacy in certain cancers.”

My Take

The good news is these drugs have been used for many years and most of them have a well known safety profile.  They are also off patent and inexpensive.  This bodes well for easy access.  The bad news is there are limited clinical trials in humans for use in cancer.  And as mentioned earlier, they are not FDA approved for treating cancer.  Some, such as fenbendazole, are not FDA approved for use in humans at all.

As there is no financial incentive for large scale clinical trials we may never see the kind of research that is needed to confirm their role in cancer therapy.  My hope is that our governmental institutions, such as the NIH, will encourage and fund the clinical research necessary to further investigate their safety and efficacy in treating cancer.


Scott Rollins, MD, is Board Certified with the American Board of Family Practice and the American Board of Anti-Aging and Regenerative Medicine.  He specializes in bioidentical hormone replacement for men and women, thyroid and adrenal disorders, fibromyalgia and other complex medical conditions.  He is founder and medical director of the Integrative Medicine Center of Western Colorado ( and Bellezza Laser Aesthetics (   Call (970) 245-6911 for an appointment or more information.



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