David Fajgenbaum has earned a spot on the prestigious TIME100 Health 2025 list. His inclusion recognizes his groundbreaking work in drug repurposing, a journey that began with a life-threatening personal health crisis.

A Critical Diagnosis and a Vow

While a third-year medical student, Fajgenbaum suddenly became critically ill. After taking an exam, he rushed to the emergency room where blood tests revealed a dire situation. A doctor informed him that his vital organs—liver, kidneys, bone marrow, heart, and lungs—were all failing simultaneously.

Fajgenbaum faced rapid decline over eleven weeks, eventually being told by doctors that he would not survive. At age 25, a priest administered his last rites as he suffered from Castleman disease, an extremely rare inflammatory condition not even covered in medical school curricula.

Facing death, Fajgenbaum made a solemn promise to his family: “I was going to dedicate the rest of my life—however long that might be—to trying to find a drug that could save my life,” he stated.

Discovering the Cure Within Existing Medicine

Determined, Fajgenbaum began running experiments on his own blood samples. He identified a previously missed defect: mTOR hyperactivation. This finding led him to investigate sirolimus, an mTOR inhibitor already in use to prevent organ transplant rejection.

Suspecting its relevance due to the targeted pathway, he proposed the drug to his physicians. After one doctor prescribed it, Fajgenbaum began taking sirolimus, which ultimately saved his life. More than a decade later, he still takes three pills daily, and this drug has since altered the treatment protocol for Castleman disease.

FoundCare and the Future of Drug Repurposing

This near-death experience fueled Fajgenbaum’s ambition to identify other FDA-approved drugs that could treat various diseases lacking effective options. He noted that physicians already possess the authority to prescribe existing drugs for new uses if the potential benefits outweigh the risks.

He founded FoundCare, a nonprofit organization that utilizes artificial intelligence to explore new applications for already-approved medications. The system compares approximately 4,000 drugs against 18,500 diseases, scoring them based on predicted efficacy.

Accelerating Impact and Saving Lives

Once promising drug-disease matches are identified, FoundCare initiates laboratory testing or connects researchers with clinicians willing to prescribe the repurposed treatments. Fajgenbaum emphasized the immediate impact: “People were literally dying of these diseases before, and now they can live with these solutions that were already there.”

In 2024, the Advanced Research Projects Agency for Health provided support for this work. To date, Fajgenbaum’s team has successfully identified or advanced 14 repurposed treatments across five rare diseases.

Fajgenbaum shared moving anecdotes about the results, including a man who could walk his daughter down the aisle due to a new treatment, and a young woman inspired to become a nurse after her life was saved. “All I can think about is the impact and how many lives we can touch,” he said, stressing the urgency: “It's just a matter of how fast we can do it, because we’re in a race against time.”