Sohonos (palovarotene)
An approved treatment for Fibrodysplasia Ossificans Progressiva.
The same compound appears under different names depending on the context. Here is how to identify Palovarotene wherever you encounter it, plus the key facts at a glance.
- Generic name
- Palovarotene
- Brand name
- Sohonos
- Drug class
- Retinoic acid receptor gamma agonist
- Manufacturer
- Ipsen
- How it's taken
- Taken by mouth with food, ideally at the same time each day.
The first approved treatment for FOP, and still the only one approved for children younger than 12. A second drug, Pasatru (garetosmab), was approved for adults in August 2026. Sohonos is a daily oral pill, with a higher dose during flare-ups, that roughly halved the volume of new bone forming in soft tissue in the trial behind its 2023 approval. It carries a boxed warning for birth defects and for stopping bone growth in children.
Where Palovarotene fits
The first approved treatment for FOP and the only one approved for children younger than 12. Pasatru (garetosmab), an antibody given by IV infusion, was approved for adults in August 2026. Sohonos' purpose is to reduce how much new bone forms, particularly around flare-ups; it does not reverse existing ossification, and the trade-off against growth-plate closure is why it is not used in younger children. Zilurgisertib (Atebrioz), an ALK2 inhibitor, was approved on September 25, 2026 for patients 12 and older, making it the third option.
How Palovarotene works
In FOP, a mutation in the ACVR1 gene makes a bone-formation receptor called ALK2 fire when it should not. Soft tissue injured by a bump, an injection or nothing at all responds by turning into bone, and that bone is permanent. Palovarotene is a retinoid, a vitamin A relative, that binds the gamma form of the retinoic acid receptor. Through that receptor it turns down the signaling downstream of ALK2, reducing the differentiation of cells into cartilage and bone. The label states it reduces the volume of new heterotopic ossification; it does not remove bone already formed.
Mechanism: Oral retinoid selective for the retinoic acid receptor gamma that dampens the overactive ALK2 (ACVR1) bone-forming signal driving FOP, reducing the volume of new bone that forms in muscle and soft tissue
Side effects and safety
- Premature growth-plate closure. skeletal maturity assessed before treatment and growth monitored during it; the reason the indication starts at 8 for girls and 10 for boys
- Dry skin, lips and eyes. with rash, hair loss and skin peeling; managed with emollients, sunscreen and artificial tears, sometimes a dose reduction
- Bone density loss. decreased vertebral bone mineral density; periodic imaging for spinal fracture
- Psychiatric effects. depression, anxiety, mood changes and suicidal thoughts; new or worsening symptoms should be reported
- Night blindness. can make driving at night hazardous
- Negative pregnancy test before starting for anyone who could become pregnant
- Baseline skeletal maturity, then linear growth in children
- Periodic spine imaging for vertebral fracture
- Mood and sleep changes
Sohonos carries a boxed warning with 2 parts. First, embryo-fetal toxicity: like all retinoids it causes birth defects, it is contraindicated in pregnancy, and it may only be prescribed when pregnancy prevention conditions are met, including a negative pregnancy test before starting. Second, premature epiphyseal closure: it can permanently close the growth plates in growing children, stopping bone growth early, which is why the indication starts at age 8 for girls and 10 for boys and why skeletal maturity is assessed before treatment and growth monitored during it. Further warnings cover dry skin, lips and eyes with rash, hair loss and skin peeling, managed with emollients, sunscreen and artificial tears; loss of vertebral bone density with periodic spinal fracture checks; psychiatric effects including depression, anxiety, mood changes and suicidal thoughts; and night blindness. The most common reactions, in at least 10% of patients, were dry skin, dry lips, joint pain, itching, limb pain, rash, hair loss, redness, headache, back pain, skin peeling, nausea, musculoskeletal pain, muscle pain, dry eye, hypersensitivity, swelling and fatigue. Suspected reactions can be reported to Ipsen at 1-855-463-5127.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Palovarotene
Taken by mouth with food, ideally at the same time each day. For patients 14 and older: 5 mg once daily as the chronic dose, raised at the start of a flare-up to 20 mg daily for 4 weeks and then 10 mg daily for 8 weeks, a 12-week flare course that restarts if another flare occurs. Under 14, both daily and flare doses are weight-adjusted, with daily doses of 2.5 to 5 mg. A flare-up is defined as at least one symptom consistent with a previous flare, such as pain, swelling or redness, or a substantial injury likely to trigger one. Doses can be reduced for side effects.
Availability and cost
Only available as the brand-name product.
A daily oral small molecule for an ultra-rare disease that had no other approved treatment until 2026. As an oral drug it avoids infusion-center costs, but the flare-up dosing means quantities vary month to month, which prior authorization processes handle poorly.
Help paying for Sohonos
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Insurance and case manager help
Patient Access Managers verify benefits and help with prior authorizations and appeals; a Patient Education Liaison provides education on FOP and SOHONOS.
The official page does not say who qualifies. Ask the program. · source - Copay help
Copay support for eligible commercially insured patients. Not available with Medicare, Medicaid, VA or TRICARE, or to residents of Massachusetts or California.
For: private insurance · source - Free medicine program
Free drug for US residents who are uninsured or functionally uninsured, face financial hardship, and meet financial eligibility criteria.
For: no insurance, underinsured · source
Good to know: Same IPSEN CARES copay and Patient Assistance Program terms apply across Ipsen products. Mon-Fri 8 AM-8 PM ET.
- From a charity · International FOP AssociationDental Care Travel Stipend Program fundApply directly
Pays for: Travel and lodging to see an FOP dental expert for medically necessary procedures, up to $1,500 per year.
The foundation says: “Status not shown on page”
Access and eligibility
Approved for adults and for children aged 8 and older if female and 10 and older if male, a split that exists because girls finish growing earlier and the drug stops growth-plate development. The pivotal trial enrolled only patients with the R206H mutation, which accounts for the large majority of FOP, so patients with rarer ACVR1 variants are inside the label but outside the trial. Pregnancy is a contraindication, and females of reproductive potential must meet pregnancy-prevention conditions to receive it.
Source: FDA Drugs@FDA (NDA 215559)
Access program details are provided for informational purposes and may vary based on insurance coverage, geographic location, and individual circumstances. Confirm current eligibility directly with the manufacturer or your specialty pharmacy.
Clinical trial results
Approval rested on Study 301 (NCT03312634), a single-arm study of 97 patients with FOP and the R206H mutation, aged 4 and older, compared against 101 untreated patients from a natural history study. New bone was measured by low-dose whole-body CT, read blinded to which study the images came from. Patients on the chronic-plus-flare regimen formed a mean of 9.4 cubic centimeters of new heterotopic bone per year against 20.3 in the untreated group, a difference of about 10.9 cubic centimeters a year with a wide confidence interval of 0.6 to 21.2. The treated group was younger on average, 15 years against 18. As with other single-arm rare disease trials, the comparison to an external cohort is the main limit on how firm that number is.
Development history
Palovarotene was originally developed by Roche and then Clementia Pharmaceuticals for FOP; Ipsen acquired Clementia in 2019. The FDA issued a complete response letter in 2022, and after resubmission approved Sohonos on August 16, 2023 as the first treatment for FOP. The age floor in the indication, and the boxed warning on growth plates, reflect a finding during development that the drug closed growth plates in children who were still growing.
Explore Fibrodysplasia Ossificans Progressiva trials
Other Fibrodysplasia Ossificans Progressiva treatments
FOP had no approved treatment until August 2023. Management was avoidance: preventing the falls, injections and surgeries that trigger flares, and steroids at the start of a flare to blunt it. Sohonos is the first drug that acts on the disease mechanism, and it does so indirectly, through a retinoid receptor that dampens the ALK2 signal rather than blocking ALK2 itself.
In August 2026 the FDA approved a second FOP drug for adults, Pasatru (garetosmab), an antibody given by IV infusion that blocks a protein called activin A. Direct ALK2 inhibitors are the next generation. Zilurgisertib (Atebrioz), approved September 25, 2026 for patients 12 and older, offers a different mechanism with a different side-effect profile, without the retinoid burden of Sohonos; its full label was not yet posted at the time of this update. For a child under the Sohonos age floor, that pipeline is where the near-term hope sits.
Common questions about Palovarotene
▸What is Palovarotene (Sohonos)?
The first approved treatment for FOP, and still the only one approved for children younger than 12. A second drug, Pasatru (garetosmab), was approved for adults in August 2026. Sohonos is a daily oral pill, with a higher dose during flare-ups, that roughly halved the volume of new bone forming in soft tissue in the trial behind its 2023 approval. It carries a boxed warning for birth defects and for stopping bone growth in children.
▸How does Palovarotene work?
In FOP, a mutation in the ACVR1 gene makes a bone-formation receptor called ALK2 fire when it should not. Soft tissue injured by a bump, an injection or nothing at all responds by turning into bone, and that bone is permanent. Palovarotene is a retinoid, a vitamin A relative, that binds the gamma form of the retinoic acid receptor. Through that receptor it turns down the signaling downstream of ALK2, reducing the differentiation of cells into cartilage and bone. The label states it reduces the volume of new heterotopic ossification; it does not remove bone already formed.
▸What are the side effects of Palovarotene?
Sohonos carries a boxed warning with 2 parts. First, embryo-fetal toxicity: like all retinoids it causes birth defects, it is contraindicated in pregnancy, and it may only be prescribed when pregnancy prevention conditions are met, including a negative pregnancy test before starting. Second, premature epiphyseal closure: it can permanently close the growth plates in growing children, stopping bone growth early, which is why the indication starts at age 8 for girls and 10 for boys and why skeletal maturity is assessed before treatment and growth monitored during it. Further warnings cover dry skin, lips and eyes with rash, hair loss and skin peeling, managed with emollients, sunscreen and artificial tears; loss of vertebral bone density with periodic spinal fracture checks; psychiatric effects including depression, anxiety, mood changes and suicidal thoughts; and night blindness. The most common reactions, in at least 10% of patients, were dry skin, dry lips, joint pain, itching, limb pain, rash, hair loss, redness, headache, back pain, skin peeling, nausea, musculoskeletal pain, muscle pain, dry eye, hypersensitivity, swelling and fatigue. Suspected reactions can be reported to Ipsen at 1-855-463-5127.
▸How is Palovarotene taken?
Taken by mouth with food, ideally at the same time each day. For patients 14 and older: 5 mg once daily as the chronic dose, raised at the start of a flare-up to 20 mg daily for 4 weeks and then 10 mg daily for 8 weeks, a 12-week flare course that restarts if another flare occurs. Under 14, both daily and flare doses are weight-adjusted, with daily doses of 2.5 to 5 mg. A flare-up is defined as at least one symptom consistent with a previous flare, such as pain, swelling or redness, or a substantial injury likely to trigger one. Doses can be reduced for side effects.
▸Is Palovarotene FDA approved?
Yes, Palovarotene (Sohonos) is FDA approved (2023) for the treatment of Fibrodysplasia Ossificans Progressiva.
▸What is Sohonos approved for?
Sohonos (palovarotene) is approved to reduce the volume of new heterotopic ossification, meaning new bone forming in muscle and soft tissue, in adults and in children aged 8 and older for females and 10 and older for males with fibrodysplasia ossificans progressiva. The FDA approved it on August 16, 2023 as the first treatment for FOP.
▸Why are the age limits different for boys and girls?
Because Sohonos can permanently close the growth plates, ending bone growth early, and girls typically finish growing sooner than boys. The indication starts at 8 for females and 10 for males, and skeletal maturity is assessed before treatment. This is one half of the drug's boxed warning.
▸How much does Sohonos reduce new bone?
In the pivotal study, 97 treated patients formed a mean of 9.4 cubic centimeters of new bone per year against 20.3 in 101 untreated patients from a natural history study, roughly a halving, with a confidence interval of 0.6 to 21.2 cubic centimeters. The comparison is to an external cohort rather than a randomized placebo group.
▸Does Sohonos remove bone that has already formed?
No. The label describes it as reducing the volume of new heterotopic ossification. Bone already formed is permanent, which is why treatment aims to prevent flares and limit what each flare leaves behind.
▸What are the side effects of Sohonos?
The boxed warning covers birth defects, so it is contraindicated in pregnancy, and premature closure of growth plates in children. Other warnings include dry skin, lips and eyes, hair loss, loss of spinal bone density, depression and suicidal thoughts, and night blindness. The most common side effects were dry skin, dry lips, joint pain, itching and limb pain.
▸How is Sohonos taken?
By mouth with food. Patients 14 and older take 5 mg daily, rising to 20 mg daily for 4 weeks and then 10 mg for 8 weeks at the start of a flare-up. Younger patients get weight-adjusted doses. The 12-week flare course restarts if another flare-up or significant injury occurs.
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- Ipsen / FDA · 2026-08. SOHONOS (palovarotene) capsules, for oral use: US Prescribing Information. https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all&query=SOHONOS
- U.S. Food and Drug Administration · 2023-08-16. SOHONOS approval, NDA 215559, August 16 2023. https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=215559
- ClinicalTrials.gov. An Efficacy and Safety Study of Palovarotene for the Treatment of FOP (MOVE, Study 301). https://clinicaltrials.gov/study/NCT03312634