Repurposed medications: When biology reveals more than planned

What if the most powerful breakthroughs in medicine weren't new drugs at all — but new uses for the ones we already have? Once a compound enters the body, biology often reveals far more potential than its original purpose ever intended.

Modern medicine often frames drugs as precision tools – engineered for a specific target, a specific disease, and a specific outcome. Yet history consistently shows us something different: once a compound enters the body, it rarely limits itself to a single pathway. Biology is interconnected, adaptive, and often far more creative than our original intentions.

This reality has given rise to one of the most powerful – and underappreciated – approaches in medicine: drug repurposing. Rather than starting from scratch, repurposing asks a simple but profound question: what else does this molecule do?

Food as the first repurposed medicine

Long before pharmaceuticals, humans were already repurposing substances without realizing it. Many foods were consumed for flavor, sustenance, or tradition, only later to be understood as biologically active compounds.

Turmeric, used for centuries as a spice, was eventually shown to influence inflammatory pathways and oxidative stress (anti-inflammatory and antioxidant activity via NF-κB and cytokine modulation). Garlic, once valued for taste and preservation, affects cholesterol metabolism, immune signaling, and microbial balance (antimicrobial, lipid-lowering, and mild antithrombotic effects). Ginger calms the digestive tract and eases nausea, while modulating inflammation (GI-motility effects). Green tea, long enjoyed as a daily beverage, contains epigallocatechin gallate (EGCG), a compound now recognized for its cardioprotective, neuroprotective, and metabolic effects (how the body uses energy, processes sugar and fat, and regulates metabolism).

These discoveries didn't change how long humans had used these foods – they changed how we understood them.

The same principle applies to medications.

Medications that morphed from their original purpose

Some of the most important advances in medicine occurred not when new drugs were invented, but when familiar ones were seen in a new light.

Here are a few examples of well-established drug repurposing. Each of these stories reinforces the same idea: a drug's first use is not necessarily its most important one.

Aspirin

Originally developed to be a less-irritating form of salicylic acid from white willow bark for the purpose of reducing pain and fever, Aspirin was later found to inhibit platelet aggregation. This transformed it into a therapy for possibly preventing heart attacks and strokes.

Minoxidil

Developed as an oral drug for high blood pressure and ulcers, clinicians noticed unexpected hair growth. This observation led to its widespread topical use for hair loss.

Metformin

Originally created from the Galega officinalis plant (French lilac) to lower blood sugar in diabetes, metformin was later shown to influence cellular energy sensing and insulin signaling.

Sildenafil (Viagra)

Initially developed for angina and hypertension, sildenafil failed at its original goal but revealed a powerful effect on blood vessel dilation: for erectile dysfunction and pulmonary hypertension.

Statins

First derived from the Penicillium citrinum fungi microorganisms and intended to lower cholesterol, statins were later shown to reduce inflammation and stabilize arterial plaques.

Ketamine

Long used as a general anesthetic, Ketamine was discovered to have rapid antidepressant effects.

Ivermectin: Repurposing – and resistance

Ivermectin was developed as an antiparasitic medication (from the soil-dwelling bacterium Streptomyces avermitilis), targeting specific ion channels that parasites rely on. Its effectiveness and safety profile made it one of the most widely used drugs in the world for parasitic disease control (later leading to a 2015 Nobel Prize due to its impact on global health). But as with many medications, its biological activity did not stop there.

Beyond its antiparasitic action, ivermectin has demonstrated anti-inflammatory properties: It has been shown to influence cytokine signaling and immune pathways involved in chronic inflammation. These effects help explain its usefulness in inflammatory skin conditions and ongoing research into inflammatory diseases such as arthritis.

Topical ivermectin is already an established treatment for rosacea, where it reduces inflammation and targets Demodex mites. This is a clear example of repurposing moving from observation to accepted clinical use.

Perhaps the most compelling area of ivermectin research lies in oncology. A growing body of preclinical studies has shown that ivermectin can interfere with metabolic processes that cancer cells depend on for survival.

Specifically, studies* have demonstrated that ivermectin can:

• Disrupt mitochondrial respiration: This means interfering with how cells use oxygen to make energy inside their "power plants" (the mitochondria), making it harder for fast-growing cells to survive.

• Interfere with glucose transport: This refers to blocking or slowing how cells take in sugar from the bloodstream, limiting the fuel they rely on to grow and divide.

• Reduce ATP (energy) production: ATP is the cell's main energy currency; reducing ATP production leaves cells with less energy to carry out vital functions.

• Alter cellular redox balance: This means upsetting the balance between harmful oxidative molecules and the cell's ability to neutralize them, which can push stressed cells toward damage or death.

Cancer cells rely heavily on altered energy metabolism to sustain rapid growth and resist cell death. By disrupting these pathways, ivermectin has shown* anticancer and anti-inflammatory effects in laboratory, animal models, and in tens of thousands of humans globally.

Repurposing is a strategy

Drug repurposing does not replace rigorous science; it focuses it. Ivermectin belongs in this conversation not just because it is a powerful cure for many illnesses including cancer, but because it exemplifies a recurring pattern in medicine: molecules often do far more than we initially recognize. The question remains, who will invest millions of dollars in official trials to bring ivermectin to market, when a medication cannot be patented?

Selected references & further reading

• Ashburn TT, Thor KB. Drug repositioning: identifying and developing new uses for existing drugs. Nature Reviews Drug Discovery.

• Cheng F et al. Network-based approaches for drug repurposing. Nature Communications.

• Barabási AL et al. Network medicine: a network-based approach to human disease. Nature Reviews Genetics.

• Pollak M. Metformin and cancer: rationale and clinical applications. Nature Reviews Cancer.

• Juarez M et al. Ivermectin inhibits cancer cell growth via disruption of mitochondrial function. Biochemical and Biophysical Research Communications.

• Zhang X et al. Ivermectin induces apoptosis and suppresses tumor growth through metabolic pathway disruption. International Journal of Molecular Sciences.

• Dou Q et al. Repurposing ivermectin for cancer treatment: molecular mechanisms and therapeutic potential. American Journal of Cancer Research.

• Crump A, Ōmura S. Ivermectin, 'wonder drug' from Japan: the human use perspective. Proceedings of the Japan Academy.

• Steinhoff M et al. Ivermectin therapy for inflammatory skin diseases. Journal of the American Academy of Dermatology.

• Hanahan D, Weinberg RA. Hallmarks of cancer: the next generation.

Play in the dirt = for health's sake!

Did you know that ivermectin has a deep and natural connection with bacteria strains?

Ivermectin was developed from avermectins, a group of naturally occurring compounds discovered in the 1970s from the soil-dwelling bacterium Streptomyces avermitilis. The bacterium was isolated by Japanese microbiologist Satoshi Ōmura, and later through chemical modification to improve safety and effectiveness, ivermectin was created, becoming a widely used treatment for parasitic infections in humans and animals.

The primary way humans interact with S. avermitilis is through direct contact with earth and dust. When you smell the fresh scent of rain on dry soil (called petrichor), you are actually smelling geosmin, a compound produced by Streptomyces bacteria, including S. avermitilis. These bacteria are abundant in garden soil, agricultural fields, and compost piles worldwide. Activities like gardening or playing in the dirt release their drought-resistant spores into the air, where they can be inhaled or touch your skin. Historically, humans likely consumed more Streptomyces by eating raw, soil-dusted foods. Modern cooking and thorough washing have significantly reduced our intake of these bacteria, which some researchers believe might be linked to a rise in certain immune-related gut issues. Small amounts of S. avermitilis have been found in the healthy human skin, respiratory tract, and gastrointestinal system.