Drug Repurposing: Often a Lifeline for Patients Living with Rare Diseases

The U.S. Food and Drug Administration (FDA) announced in May 2026 that it was soliciting public comments on its efforts to find new indications for existing FDA-approved drugs to expand treatment options for rare diseases. The FDA specifically requested information on drugs with sufficient evidence to support repurposing to treat other disease states, those with preliminary evidence supporting further study, and those with preclinical data supporting further study (FDA, 2026).

Drug repurposing occurs when a medicine already approved for one disease gains approval for a different therapeutic use. A recent study found that 451 drugs received approval for new therapeutic uses between 1985 and 2024, with oncological and neurological disorder uses benefiting the most (Akodad et al., 2026).

Akodad et al. also found that ~30% of efforts to repurpose drugs to treat other conditions are successful in receiving regulatory approval, compared to just 10% of new drug applications. For pharmaceutical companies, this can significantly cut research and development costs, with many of the early-phase testing related to pharmacokinetics (the onset, duration, and intensity of a drug’s effects) and pharmacodynamics (what a drug does to the body)—often referred to as PK/PD—already studied and determined. Additionally, the safety profiles of those drugs have already been determined, reducing the time and expense required on the march to FDA approval.

Drug repurposing can also efficiently identify treatments for hard-to-treat and rare conditions. One such condition, Myasthenia Gravis (MG), has seen recent developments that demonstrate the importance of drug repurposing.

MG is a chronic autoimmune neuromuscular disorder characterized by fluctuating muscle weakness (twitching) and fatigue. It has been referred to as “snowflake disease,” not because the patients are weak, but because no two snowflakes are alike. As such, symptoms of MG vary widely from patient to patient and may include: weakness of the eye muscles, drooping of one or both eyelids, blurred or double vision, changes in facial expressions, difficulty swallowing, shortness of breath, impaired speech, and/or weakness in the arms, hands, fingers, legs, and neck. Moreover, it affects drastically different demographic groups, with Women under the age of 40 and Men over the age of 60 being impacted (National Institutes of Health, 2026).

Over the past decade, a number of older medications have been tested for repurposing for the treatment of MG symptoms, including ephedrine (a central nervous system stimulant and sympathomimetic agent) as an add-on treatment to enhance muscle strength, eculizumab (a long-acting injectable medication used to treat a type of blood disease called paroxysmal nocturnal hemoglobinuria), and rituximab (a drug used to treat non-Hodgkin lymphoma, chronic lymphocytic leukemia, rheumatoid arthritis, granulomatosis with polyangiitis, microscopic polyangiitis, and pemphigus vulgaris). While these medications are not cures and their efficacy in treating MG is still being studied, they show significant promise (Stieglbauer et al, 2017; Weinreich, 2017; Lente Wijnsma et al., 2019).

Take Tasha White from St. Louis, Missouri, as an example. Living with MG since she was only 6 years old, Tasha is no stranger to drug repurposing to alleviate the very debilitating symptoms that plague her autoimmune system. Though approved to treat certain types of cancer, Rituxan (rituximab) has served as a lifeline for Tasha's quality of life. In her case, the repurposed drug destroys specific immune cells, called B cells, that produce the harmful autoantibodies attacking her neuromuscular junctions.

(Learn more about Tasha's nonprofit, My Walk With MG)

Drug repurposing offers an opportunity to take drugs already proven safe for use in humans and test their efficacy in treating rare conditions and diseases, such as MG. It may also serve to reduce research and development costs, particularly as R&D costs and late-stage attrition (people leaving clinical trials) continue to rise (Fernald et al., 2024).

But, again…these things take time, patience, and funding. All things that are currently in short supply.