The Most Overlooked Opportunity in Modern Medicine? Repurposing Existing Drugs

It’s not often that a conversation fundamentally reframes how you think about medicine, longevity, and the future of health. But that’s exactly what happened when physician-scientist David Fajgenbaum, M.D., MBA, MSc, joined us on the mindbodygreen podcast. 

His story is remarkable: A former Division I athlete who became a medical student, then a critically ill patient nearly dying five times from Castleman disease—and ultimately the researcher who helped discover the treatment that saved his own life.

That experience didn’t just change the trajectory of his health. It changed his purpose. Today, he’s one of the youngest tenured professors at the University of Pennsylvania School of Medicine, co-founder of Every Cure, and a leading voice in the movement to repurpose existing drugs for new, overlooked uses. His work is rooted in a simple but profound idea: many of the medicines we need already exist—we just haven’t connected them to the right diseases yet.

Most people assume modern medicine has treatments for the majority of diseases. But according to Fajgenbaum, that’s far from true. There are roughly 18,000 known diseases and only 4,000 approved drugs, many of which were designed decades ago for very specific uses. That leaves tens of thousands of conditions with no available treatment and countless patients without options.

What’s surprising is that many approved drugs have far broader effects than their labels suggest. Biology doesn’t follow marketing boundaries; a medicine developed for one condition may also benefit a completely different one. 

“There are a lot of examples where diseases look very different, but the underlying problem in the body can be treated with the same drug,” Fajgenbaum explained on the podcast.

So why aren’t we using more drugs this way? Fajgenbaum says it comes down to incentives. Once a drug becomes generic, no one benefits financially from proving it can treat another disease. Large trials cost millions of dollars, and when no one stands to profit, no one funds the research, even if lives could be saved.

This realization became deeply personal when Fajgenbaum nearly died from Castleman disease. After multiple relapses and no treatment options left, he turned to the scientific literature himself. He eventually found clues pointing to an existing drug, sirolimus, that could help regulate the immune pathway fueling his condition. That drug, already sitting in pharmacies nationwide, ended up saving his life.

Identifying repurposing opportunities used to take years of manual research. Now, thanks to the platform his nonprofit Every Cure is building, AI can analyze the world’s biomedical knowledge and evaluate 75 million drug–disease combinations in a matter of hours.

This field, what he calls computational pharmacophenomics, scores how likely each drug is to help each disease. From there, researchers can focus on the most promising leads.

The efficiency is unprecedented. Early prototypes took 100 days to run these analyses. Now it takes 17 hours.

This kind of acceleration could reshape how quickly patients get help. Instead of spending 10 to 15 years developing a new molecule, researchers can identify an existing drug, study its safety profile, look for real-world signals from doctors already using it off-label, and move into trials far more quickly.

Fajgenbaum believes autoimmune diseases are among the ripest for breakthroughs. With many shared biological pathways (and decades of medications already developed to target them), there is huge potential to match existing immune-modulating drugs to conditions no one has tested them on.

Fajgenbaum’s story is extraordinary, but the vision behind it is refreshingly practical: the future of medicine might be hidden in the medicines we already have. With the help of AI, we may soon uncover treatments for diseases that have stumped researchers for decades.