Why is drug repurposing cheaper than traditional drug development?

Because repurposed drugs have already passed clinical safety testing, researchers already know their pharmacokinetics, pharmacodynamics, dosing, toxicity, and side-effect profiles. This skips the slowest and riskiest stages of early drug development, dramatically reducing both cost and time to reach patients.

What percentage of FDA-approved drugs come from drug repurposing?

Repurposed drugs account for approximately 30% of all drugs and vaccines approved by the US FDA, and they generate roughly 25% of the pharmaceutical industry's annual revenue.

Do NSAIDs reduce cancer risk or slow cancer progression?

Evidence indicates that NSAID use is associated with reduced cancer progression, and roughly 20% of all cancers arise from chronic inflammatory disease. Drugs such as celecoxib, diclofenac, mesalazine, sulindac, ibuprofen, and piroxicam show anti-tumor effects, although long-term dosing and risk-benefit balance still need further study.

What is the most promising repurposed drug for cancer?

There is no single winner yet. Metformin, ritonavir, nelfinavir, and itraconazole are among the most studied candidates, each acting through multiple anti-tumor mechanisms including AMPK/mTOR modulation, ER stress induction, and Hedgehog pathway inhibition.

How do repurposed drugs stay effective against drug-resistant tumors?

Many repurposed drugs act through pathways that differ from conventional chemotherapy, such as histone deacetylase inhibition, cholesterol homeostasis disruption, endoplasmic reticulum stress, and survivin downregulation. Because these mechanisms are largely independent of chemoresistance pathways, the drugs can remain effective against resistant tumors.

Are repurposed cancer drugs already approved for cancer treatment?

Most repurposed drugs discussed in current research are approved for their original indications but remain investigational for cancer. A few, such as doxorubicin and certain established agents, are already used in oncology. Most candidates are still in preclinical or early clinical stages for their new cancer applications.

Drug Repurposing for Cancer: How Old Drugs Are Becoming New Treatments (2026)

Q: What is drug repurposing in cancer?

Drug repurposing, also called drug repositioning or drug reprofiling, is the strategy of finding new therapeutic uses for drugs that are already approved for other conditions. In cancer, this means testing existing medications — from antipsychotics and NSAIDs to antivirals, diabetes drugs, antibiotics, and antifungals — for anti-tumor activity they were never designed to have.

Q: Can antipsychotic drugs really treat cancer?

Preclinical and observational studies suggest they can. Drugs such as aripiprazole, sertindole, brexpiprazole, and valproic acid have demonstrated anti-proliferative and pro-apoptotic effects against colon, gastric, breast, and brain tumors. These findings are still awaiting confirmation in large-scale clinical trials.

Here’s the short version: drug repurposing — also called drug repositioning or drug reprofiling — means taking a medicine that’s already approved for one condition and finding a new job for it. In oncology, that includes antipsychotics, anti-inflammatory drugs, antivirals, diabetes drugs, antibiotics, and even antifungals. None of them were designed to fight cancer. Some of them, it turns out, are pretty good at it anyway.

The best part? These drugs already have safety data. Researchers know their dosing, their side effects, how the body breaks them down. That means they can reach patients far faster — and at a fraction of the cost — than anything built from scratch.

What You Should Remember

Repurposing is behind roughly 30% of FDA-approved drugs and vaccines and about 25% of the pharmaceutical industry’s annual revenue.
Because the safety testing is already done, repurposed drugs skip the slowest, riskiest parts of drug development.
Aripiprazole, sertindole, and brexpiprazole — all antipsychotics — show real anti-cancer activity in colon, gastric, breast, and brain tumors.
NSAIDs like celecoxib, diclofenac, and mesalazine slow tumor growth, mostly through COX-2 inhibition.
Antivirals (acyclovir, zidovudine, nelfinavir, ritonavir) and antifungals (itraconazole, ketoconazole, mebendazole) have documented anti-tumor effects too.
Metformin, the standard first-line diabetes drug, has anti-cancer activity in prostate, breast, lung, endometrial, and pancreatic cancers.

What Drug Repurposing Actually Means

Cancer care has a frustrating problem. The treatments that work tend to be expensive, and most of them come with serious side effects. Developing a new drug from nothing takes years of research, a mountain of money, and most candidates never make it to market.

Drug repurposing takes a different route. Instead of starting from zero, scientists look at medicines that are already approved for humans and ask: what else could this do? The answers have been surprising.

Consider the numbers. Roughly 30% of drugs and vaccines approved by the US FDA trace back to repurposing. That work generates about a quarter of the industry’s yearly revenue.

The most famous example is sildenafil — Viagra. It was built as a blood pressure and angina drug, and only became famous for erectile dysfunction after phase II trials revealed an unexpected side effect. Aspirin, minoxidil, and valproic acid all found second careers the same way.

Why Oncology Keeps Coming Back to This Idea

Drug resistance is the wall that cancer therapy keeps hitting. Tumor cells develop resistance to chemotherapy through a mix of mechanisms — poor blood supply to the tumor, high interstitial fluid pressure, hypoxia, and the toxicity of the drugs themselves. Each mechanism chips away at treatment effectiveness.

Repurposed drugs get around part of this problem. They already have known toxicity profiles and known mechanisms of action, so they can move into patient trials quickly. And because many of them work through pathways that conventional chemo doesn’t touch, they can stay effective against resistant tumors.

How Researchers Actually Find These New Uses

It’s a mix of computation, experiment, and combination. A few approaches come up over and over:

Knowledge-based repurposing digs through existing drug data — targets, chemical structures, pathways, known adverse effects — to predict targets, biomarkers, or disease pathways nobody had linked together before.

Target-based repurposing runs high-throughput screens of drug compounds against proteins or biomarkers of interest, then filters candidates through in silico screening of drug databases, using ligand-based screening or molecular docking.

Gene expression profiling looks at which genes are switched on in a cell under different conditions. DNA microarrays track specific genes; sequencing captures everything that’s active at once.

Network-based methods — like weighted gene co-expression network analysis, or WGCNA, if you like acronyms — pull in data from multiple sources to map relationships between gene sets and clinical traits.

Virtual docking predicts how small-molecule ligands bind to macromolecular targets, which lets researchers screen tens of thousands of molecules from ligand databases in a reasonable time.

None of this would work at the current scale without the flood of genomics and proteomics data, or the computing power to make sense of it. Open-access databases and high-throughput platforms changed the game.

Can Antipsychotic Drugs Treat Cancer?

Yes, and the evidence is more convincing than most people expect. Observational studies have found that patients on antipsychotics for schizophrenia show lower rates of colon, rectal, and prostate cancer. At the molecular level, these drugs hit multiple pathways that end in tumor cell death.

Aripiprazole, used for bipolar disorder and schizophrenia, slows cell proliferation and tumor growth in colon cancer, glioma, and gastric cancer. Lab studies show it kills PANC-1, PSN-1, and A549 cancer cells at concentrations that leave normal cells alone. It triggers apoptosis in both cancer cells and cancer stem cells, and it pushes cancer stem cells to differentiate into non-cancer stem cells.

Sertindole looks promising for breast and gastric cancer. It drives production of reactive oxygen species, which set off autophagy and cell death in neuroblastoma cells. And because antipsychotics cross the blood-brain barrier, sertindole might help keep breast cancer from spreading to the brain.

Brexpiprazole, the newer kid on the block, works as a chemosensitizer in pancreatic cancer and non-small cell lung cancer by dialing down survivin, an anti-apoptotic protein. It makes glioblastoma stem cells vulnerable to osimertinib, an EGFR-TKI, and lowers the expression of stem cell markers CD133, Bmi1, Nanog, and Sox2.

Valproic acid, familiar from epilepsy and bipolar disorder treatment, acts through epigenetic mechanisms. It inhibits histone deacetylases, which cuts tumor cell proliferation, triggers differentiation, and blocks the growth of new blood vessels.

The list keeps going. Phenothiazines push tumor stem cells toward differentiation. Olanzapine wrecks cholesterol homeostasis in tumor cells. SSRIs, tricyclic antidepressants, and MAO inhibitors like selegiline, phenelzine, and tranylcypromine (which target LSD1) all show some anti-cancer activity.

Do Anti-Inflammatory Drugs Prevent or Treat Cancer?

Inflammation is one of the drivers of cancer. Around 20% of all cancers grow out of chronic inflammatory disease. The inflammatory mediators — cytokines, chemokines, growth factors, proteolytic enzymes — help cancer cells survive, multiply, and pile up mutations.

NSAIDs, used by about 30 million people worldwide, work by blocking cyclooxygenase (COX), the enzyme that makes prostaglandins and thromboxane. COX-1 handles everyday jobs like protecting the stomach lining; COX-2 shows up during pain and inflammation. The anti-cancer evidence mostly involves COX-2.

The highlights:

Mesalazine (5-ASA), the ulcerative colitis drug, inhibits tumor growth in colorectal cancer. It activates PPAR transcription factors to block the Wnt/β-catenin pathway, downregulates COX-2, interferes with PP2A, suppresses EGFR, blocks c-Myc, and promotes regulatory T cells through the aryl hydrocarbon receptor. It does a lot.
Sulindac cuts the recurrence of familial adenomatous polyposis.
Ibuprofen and piroxicam are linked to lower risk of breast cancer and colorectal cancer.
Diclofenac slowed pancreatic tumor progression in mice by boosting apoptosis and cutting angiogenesis. Combined with sorafenib, it worked against melanoma cells.
Celecoxib, a selective COX-2 inhibitor, suppresses breast cancer cell growth by inhibiting aromatase and estrogen receptor α, and reduced tumor development in rat models.

Read enough of these studies and the pattern is hard to miss: NSAID use keeps coming up associated with reduced cancer progression.

Can Antiviral Drugs Fight Cancer?

Antivirals are built to suppress viral replication, not to kill viruses directly. That hasn’t stopped several from showing genuine anti-cancer activity:

Acyclovir slows breast cancer cell growth by regulating cytokine production and switching on Caspase-3-mediated apoptosis. It also blocks colony formation and cell invasion.
Zidovudine (azido thymidine), the first approved HIV treatment, shows anti-cancer effects in leukemia, lymphoma, Kaposi sarcoma, and pancreatic cancer. It inhibits telomerase, which pushes cells into apoptosis.
Brivudine (RP101) suppresses chemoresistance, and with bortezomib it limits the growth of resistant multiple myeloma cells. It’s in phase II trials alongside gemcitabine for pancreatic cancer.
Nelfinavir, an HIV protease inhibitor, induces endoplasmic reticulum stress and the unfolded protein response while inhibiting Akt signaling. It has activity in non-small cell lung cancer, ovarian cancer, liposarcomas, and breast cancer, and reached phase II trials for head and neck cancer.
Ritonavir impedes the cell cycle, triggers apoptosis, and interferes with the AKT and NF-κB pathways. It inhibits survivin in lung cancer, disrupts Akt-regulated proliferation in breast cancer, lowers GLUT4 glucose transporter levels, and inhibits the proteasome and HSP90. Paired with delanzomib, it synergistically induced ER stress and suppressed mTOR signaling in renal cancer cells.

Do Diabetes Drugs Have Anti-Cancer Effects?

Diabetes affects roughly 400 million people worldwide. Some of its treatments have turned out to do more than manage blood sugar.

Metformin, the first-line oral drug for type 2 diabetes, lowers hepatic gluconeogenesis and improves insulin sensitivity. Its anti-neoplastic activity shows up in prostate, breast, lung, endometrial, and pancreatic cancers. It works two ways: it lowers insulin levels, which slows tumor progression, and it acts directly on cancer cells by inhibiting the mitochondrial electron transport chain. In breast cancer, it activates AMPK signaling, which then inhibits the mTOR pathway.

Thiazolidinediones (TZDs) — troglitazone, rosiglitazone, and pioglitazone — look promising in breast and prostate cancer. They work through PPARγ-dependent mechanisms (forming a heterodimer with the retinoid X receptor to activate genes that slow proliferation and promote differentiation and apoptosis) and PPARγ-independent mechanisms (PTEN/AMPK, AKT/mTOR, and degradation of cyclins D1 and D3).

What About Antibiotics?

Bacterial infections can set up conditions that favor carcinogenesis — toxin secretion, genomic instability, resistance to cell death. The antibiotics add another layer:

Clarithromycin (Biaxin) was first tested for lung cancer back in 1997. Its anti-tumor activity was much stronger in combination with other drugs.
Doxycycline blocks iNOS, which tumors need for development, growth, and angiogenesis. In colon cancer, combined with a COX-2 inhibitor, it causes G0/G1 cell cycle arrest and inhibits matrix metalloproteinase. In breast cancer, it suppresses the cancer stem cell phenotype and mitochondrial biogenesis.
Doxorubicin, technically an antibiotic subclass, treats breast cancer by intercalating into DNA and causing breaks that stop replication.

Do Antifungal Drugs Show Anti-Cancer Activity?

Fungal infections kill around 2 million people worldwide each year, mostly patients with compromised immune systems. The antifungals have joined the repurposing conversation too:

Itraconazole inhibits the AKT/mTOR pathway in endothelial cells, endometrial carcinoma, melanoma, and glioblastoma. It reverses P-glycoprotein-driven chemoresistance, regulates Hedgehog signaling, and inhibits both angiogenesis and lymphangiogenesis.
Ketoconazole has anti-cancer activity in prostate, melanoma, breast, and hepatocellular carcinoma. In prostate cancer cells it inhibits exosome biogenesis, with better tolerance and fewer side effects than many alternatives.
Mebendazole triggers cell cycle arrest in non-small cell lung cancer through tubulin depolymerization. It also radiosensitizes breast cancer cells and shrinks the cancer stem cell population through the Hedgehog pathway.

The Catch: What’s Still Missing

The evidence looks good, but it’s mostly preclinical. The exact molecular targets of many repurposed drugs aren’t fully mapped, and dosing for cancer is often different from dosing for the original condition. Large-scale clinical trials will decide which of these candidates actually earn a place in treatment protocols.

That said, the timeline advantage is real. These drugs don’t need to be re-proven safe from the ground up. The most likely future isn’t one magic repurposed drug — it’s combinations: existing affordable medicines working alongside chemotherapy, immunotherapy, and targeted agents. For patients who’ve run out of options, that’s a meaningful hope, and it’s closer than a brand-new molecule would be.

Common Questions, Straight Answers

What is drug repurposing in cancer? Taking a drug already approved for another condition and testing it for anti-tumor activity. The candidates range from antipsychotics to antifungals.

Why is it cheaper than traditional drug development? The safety work is already done. Researchers know the dosing, toxicity, and side effects, which skips years of early-stage development and cuts both cost and risk.

What share of FDA approvals comes from repurposing? Roughly 30% of all drugs and vaccines approved by the US FDA, representing about 25% of annual pharmaceutical industry revenue.

Can antipsychotic drugs really treat cancer? Preclinical and observational evidence says the direction is real — aripiprazole, sertindole, brexpiprazole, and valproic acid all show anti-proliferative and pro-apoptotic effects against colon, gastric, breast, and brain tumors. Clinical validation is still underway.

Do NSAIDs reduce cancer risk? The evidence points that way, and about 20% of cancers grow out of chronic inflammation. Celecoxib, diclofenac, and mesalazine all show anti-tumor effects, though long-term dosing and risks need more study.

Which repurposed drug is the most promising? There’s no single winner yet. Metformin, ritonavir, nelfinavir, and itraconazole are among the most studied, and each works through multiple anti-tumor mechanisms.

How do repurposed drugs stay effective against resistant tumors? Many act through pathways chemotherapy doesn’t touch — histone deacetylase inhibition, cholesterol disruption, ER stress, survivin downregulation. That’s what lets them keep working where chemo stops.

This article is for informational purposes only and does not constitute medical advice. Always talk to a qualified healthcare professional before starting, stopping, or changing any medication.