Some of the most significant drug approvals of the past decade came not from entirely new molecules, but from existing drugs — already approved, already manufactured, already understood — that were found to work in entirely new diseases. Drug repurposing, also called drug repositioning, is the systematic effort to find new therapeutic applications for compounds that have already passed safety testing. For biotech investors, repurposing programs offer a distinctive risk-reward profile: lower development costs and faster timelines than novel drug discovery, but real clinical uncertainty about whether known biology translates to a new indication.
The Short Answer
| Drug repurposing is the process of investigating and developing an existing drug — already approved for one indication — for use in a different disease or condition. Because the drug has already been through safety testing and manufacturing scale-up, repurposing programs can skip or shorten the early development stages, reducing development cost and timelines compared to starting from a new compound. Repurposing is particularly common in oncology, rare diseases, and areas where new drug discovery has proven especially difficult. |
How Drug Repurposing Became a Serious Development Strategy
Drug repurposing has always happened in some form — sildenafil (Viagra) was originally developed as a cardiovascular drug and found its most famous indication almost accidentally during trials. Thalidomide, the drug whose safety failures in the 1960s triggered the modern clinical trial framework, was later found to be effective in multiple myeloma and leprosy complications and was reapproved under strict safety protocols. These early examples were largely serendipitous.
The systematic approach to repurposing accelerated in the 2000s and 2010s as genomic databases, high-throughput drug screening, and computational drug discovery tools made it possible to search for mechanistic overlap between approved drugs and new disease targets at scale. The growing cost and failure rate of novel drug discovery — with average development costs exceeding $1 billion and Phase 3 failure rates above 50% — made the economics of repurposing increasingly attractive relative to starting from a new chemical entity.
The COVID-19 pandemic dramatically accelerated public awareness of drug repurposing. Dexamethasone — a decades-old corticosteroid — was identified through the RECOVERY trial as the first treatment shown to reduce mortality in hospitalized COVID-19 patients, representing one of the most impactful drug repurposing findings in recent history.
The Development Advantages of Repurposing
The core advantage of repurposing over novel drug discovery is the pre-existing safety and manufacturing data. An approved drug already has a known safety profile in humans, established manufacturing processes, and an existing regulatory relationship with the FDA. This means a repurposing program typically starts at Phase 2 rather than Phase 1, eliminating the safety-finding stage and compressing the overall timeline.
For a drug with Orphan Drug Designation in its new indication, the cost advantages multiply: the 50% tax credit on clinical costs applies, the FDA filing fee is waived, and seven years of market exclusivity provides commercial protection. Many rare disease repurposing programs have been funded and executed by small biotech companies precisely because the lower clinical development cost makes the economics viable even for modest-sized patient populations.
How the FDA Handles New Indications for Approved Drugs
When a company seeks FDA approval for an existing drug in a new indication, it files a supplemental NDA (sNDA) or supplemental BLA (sBLA), adding the new indication to the existing approval. The FDA reviews the new clinical data package supporting the new indication through the same PDUFA review process as an original application. The company still needs to conduct and file clinical trials demonstrating safety and efficacy in the new indication — the shortcut is in not needing to repeat the foundational safety and manufacturing work, not in skipping the efficacy evidence.
Notable Repurposing Examples Investors Should Know
Metformin — the first-line diabetes drug — is among the most actively investigated repurposing candidates, with clinical trials underway studying its potential in cancer prevention, aging, and neurodegeneration. Thalidomide and its derivative lenalidomide transformed from a notorious safety disaster to a cornerstone of multiple myeloma treatment. Rapamycin (sirolimus), originally developed as an immunosuppressant for organ transplant, is now being investigated for aging-related conditions and rare genetic diseases. Each of these represents a commercial opportunity built on biology that was discovered after the drug’s original approval.
What This Does Not Guarantee
| Drug repurposing does not guarantee clinical success in the new indication. A drug that is safe and effective in one disease context can fail entirely in a different one — biology does not transfer automatically across indications. The abbreviated development timeline also means there can be less preclinical rationale built up for the new indication compared to a purpose-built drug program. Investors should require the same level of clinical evidence scrutiny for repurposing programs as for any other pipeline asset. |
Key Takeaways
- Drug repurposing investigates existing approved drugs for new therapeutic indications, leveraging pre-existing safety data and manufacturing infrastructure
- Repurposing programs typically start at Phase 2 rather than Phase 1, reducing development timelines and costs compared to novel drug discovery
- The COVID-19 pandemic produced one of the most impactful repurposing examples: dexamethasone, identified through the RECOVERY trial as reducing mortality in hospitalized patients
- New indications for approved drugs are filed as supplemental NDAs or BLAs — the company still must demonstrate safety and efficacy in the new indication
- Orphan Drug Designation for a repurposed drug provides the same financial incentives as for a novel drug, making rare disease repurposing economically viable for small companies
- Notable repurposing successes include thalidomide/lenalidomide (multiple myeloma), sildenafil (pulmonary arterial hypertension), and rapamycin (multiple investigational applications)
- Repurposing does not eliminate clinical risk — efficacy in one indication does not predict efficacy in another
Sources
1. FDA — Supplemental Applications: https://www.fda.gov/drugs/types-applications/supplemental-applications-prescription-drugs
2. RECOVERY Trial — Dexamethasone: https://www.recoverytrial.net
3. NIH — Drug Repurposing: https://ncats.nih.gov/research/research-activities/ntu/repurposing
4. PubMed: https://pubmed.ncbi.nlm.nih.gov
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