The FDA approved rusfertide on August 28, the first hepcidin-mimicking peptide to reach the market. It is cleared for adults with polycythemia vera whose disease is not controlled well enough by existing treatment, and it will be sold as MIMRYLO.
Polycythemia vera is a blood cancer in which the bone marrow makes too many red blood cells. The blood thickens, which raises the risk of clots, strokes, and heart attacks, and patients live with fatigue and itching. Polycythemia vera is a myeloproliferative neoplasm, a cancer of the blood-forming machinery itself. The oldest treatment is also the bluntest: phlebotomy, drawing off a pint of blood on a schedule to keep the red-cell count down, sometimes for years, often alongside cytoreductive drugs such as hydroxyurea, interferon, or ruxolitinib that suppress the marrow.
A hormone the drug copies
Rusfertide is a synthetic peptide that imitates hepcidin, the hormone the liver makes to control iron traffic. Hepcidin locks iron away in storage and limits how much reaches the marrow, and the marrow needs iron to build red cells. By mimicking that signal, the drug starves red-cell production of its raw material rather than poisoning the dividing cells the way older marrow-suppressing agents do. It is a once-weekly injection under the skin, discovered by Protagonist Therapeutics ↗ and developed and commercialized by Takeda.
The approval rests on VERIFY, a phase 3 double-blind trial of 293 patients that added rusfertide or a placebo to each patient's existing care. Presented at the 2025 meeting of the American Society of Clinical Oncology ↗ by Andrew Kuykendall of Moffitt Cancer Center, it hit its primary endpoint: 76.9 percent of patients on rusfertide were classed as responders during weeks 20 to 32, against 32.9 percent on placebo. Patients on the drug needed far less bloodletting, a mean of 0.5 phlebotomies over the study window versus 1.8, and held their hematocrit, the fraction of blood made up of red cells, under the 45 percent safety threshold far more consistently, 62.6 percent of the time versus 14.4 percent. The most common side effects were injection-site reactions and anemia.
What the endpoint does and does not cover
The win is real but narrow, and worth reading precisely. The response endpoint is a composite of avoiding phlebotomy and keeping hematocrit controlled. Those are direct measures of the disease's day-to-day burden and the strongest predictors doctors track, but they are not the outcomes that make polycythemia vera dangerous. The trial did not show that rusfertide prevents the clots and strokes that thickened blood causes, nor that it slows the disease's slow drift toward myelofibrosis or leukemia, the transformations that shorten lives. Those play out over years, and a trial scored at 32 weeks cannot see them.
The anemia signal is the mechanism showing its other face. A drug that works by restricting iron will, pushed too far, leave too little for normal red-cell production, so the same lever that controls the disease is the one that has to be watched. And the pivotal data have been presented at conferences, at ASCO and later at the American Society of Hematology, but not yet published in a peer-reviewed journal, so the full dataset is not on the table.
Still, this is a genuine milestone for peptide therapeutics. Injectable peptides have crowded into metabolic disease, where the GLP-1 drugs dominate the conversation, but rusfertide is a peptide hormone-mimic winning approval in hematology, a first-in-class mechanism in a disease that has leaned on bloodletting since antiquity. Peptidemodel hosts no card for rusfertide yet, and the platform's hepcidin entries are unrelated anticancer peptides rather than this iron-regulating mimic, a gap the approval makes worth closing.