Last updated: September 8, 2026
Momelotinib dihydrochloride is GSK’s branded myelofibrosis drug, marketed in the United States as Ojjaara. The FDA approved it in September 2023 for adults with intermediate- or high-risk primary or secondary myelofibrosis with anemia. Its commercial differentiation is the simultaneous inhibition of Janus kinase 1, Janus kinase 2, activin A receptor type 1, and related signaling pathways, which addresses anemia as well as splenomegaly and constitutional symptoms.
The product has a favorable clinical position in an anemia-heavy myelofibrosis population, but its financial trajectory depends on conversion from established ruxolitinib therapy, physician adoption of a newer treatment sequence, reimbursement, and expansion outside the United States. GSK paid approximately $1.9 billion to acquire Sierra Oncology in 2022, primarily to obtain momelotinib. Sierra had projected peak annual sales above $1 billion, while actual sales disclosure from GSK has been limited because Ojjaara remains a small component of the company’s overall portfolio (GSK, 2022; GSK, 2024).
What is momelotinib dihydrochloride and how is Ojjaara used?
Momelotinib is an oral small-molecule kinase inhibitor. The marketed active ingredient is momelotinib dihydrochloride monohydrate, commonly referred to commercially as momelotinib.
The FDA-approved indication is:
| Attribute |
Detail |
| Brand |
Ojjaara |
| Active ingredient |
Momelotinib dihydrochloride monohydrate |
| Company |
GSK |
| Dosage form |
Oral tablet |
| Strength |
100 mg, 150 mg, and 200 mg |
| FDA approval |
September 15, 2023 |
| Indication |
Intermediate- or high-risk primary myelofibrosis, post-polycythemia vera myelofibrosis, or post-essential thrombocythemia myelofibrosis in adults with anemia |
| Recommended dose |
200 mg orally once daily |
| FDA pathway |
New drug application |
| Product category |
Small-molecule oncology and hematology drug |
The label reflects the product’s main commercial distinction. Ruxolitinib, the leading JAK inhibitor in myelofibrosis, is effective against splenomegaly and symptoms but can worsen or fail to resolve anemia. Momelotinib’s ACVR1 inhibition reduces hepcidin signaling and may improve iron availability and erythropoiesis, giving GSK a differentiated position in patients with baseline or treatment-emergent anemia (FDA, 2023).
What is the commercial market for momelotinib?
The addressable market is the myelofibrosis segment of the broader myeloproliferative neoplasm market. Myelofibrosis is a rare hematologic malignancy, so revenue depends less on broad population expansion and more on treatment duration, line of therapy, pricing, and market share.
Momelotinib competes primarily against:
| Competitor |
Company |
Commercial role |
| Jakafi, Jakavi |
Incyte and Novartis |
Established JAK1/JAK2 standard |
| Vonjo |
Sobi, formerly CTI BioPharma |
Approved for myelofibrosis with severe thrombocytopenia |
| Inrebic |
Bristol Myers Squibb |
JAK2 inhibitor for intermediate- or high-risk primary or secondary myelofibrosis |
| Ojjaara |
GSK |
JAK1/JAK2 and ACVR1 inhibitor with anemia-focused positioning |
| Transfusion support and erythropoiesis-directed therapy |
Multiple providers |
Supportive treatment for anemia |
| Allogeneic stem-cell transplantation |
Specialist centers |
Potentially curative but limited to selected patients |
GSK’s target segment is particularly attractive in patients with anemia, transfusion dependence, or declining hemoglobin. That segment represents a smaller population than all patients with myelofibrosis, but it is clinically underserved and may support premium pricing.
The main commercial constraint is treatment sequencing. Many patients begin therapy with ruxolitinib and may remain on it for years if symptom and spleen control are adequate. Momelotinib therefore needs to win new diagnoses, capture patients switching because of anemia, and retain patients through disease progression.
How did the FDA approval affect the financial outlook?
FDA approval converted momelotinib from a development asset into a commercial hematology product. GSK obtained the asset through its $1.9 billion acquisition of Sierra Oncology, which closed in July 2022. Sierra had acquired worldwide rights from Gilead Sciences in 2018 after Gilead discontinued development in earlier strategic circumstances (GSK, 2022; Sierra Oncology, 2022).
The investment thesis rested on three factors:
- A sizeable unmet need in anemic myelofibrosis.
- A differentiated mechanism relative to ruxolitinib.
- Potential peak annual sales above $1 billion.
The commercial ramp is likely to be gradual. Hematology drugs often require specialist diagnosis, sequencing decisions, payer review, and treatment-center adoption. GSK’s established oncology infrastructure reduces launch friction, but the company entered a market with entrenched prescribing patterns and competing JAK inhibitors.
GSK’s public reporting has not provided a detailed standalone revenue series sufficient to establish a full audited sales trajectory for Ojjaara. The product’s early commercial value should therefore be evaluated through launch indicators such as formulary access, new-patient starts, prescription volume, treatment duration, international approvals, and the proportion of prescriptions in second-line or anemia-driven use.
What were the key clinical and regulatory milestones?
| Date |
Milestone |
| 2018 |
Sierra Oncology obtained worldwide rights to momelotinib from Gilead Sciences |
| 2022 |
GSK completed acquisition of Sierra Oncology for approximately $1.9 billion |
| 2022 |
MOMENTUM Phase 3 data supported efficacy in symptomatic and anemic myelofibrosis |
| September 15, 2023 |
FDA approved Ojjaara |
| 2023 |
GSK began U.S. commercialization |
| 2024 |
European Commission authorization expanded commercial reach outside the United States |
The FDA approval was supported by data from the MOMENTUM trial and a set of prior momelotinib studies. The approval recognized clinically relevant effects on symptoms, spleen response, and transfusion independence in patients with anemia (FDA, 2023).
The European authorization is commercially important because myelofibrosis treatment is concentrated in specialist hematology centers across major European markets. European pricing and reimbursement negotiations, however, can delay revenue realization compared with the United States.
What patents protect momelotinib and when does exclusivity end?
Momelotinib is protected by a combination of composition-of-matter, salt, formulation, and method-of-use rights. The commercial exclusivity profile is expected to extend into the early 2030s through issued patents and regulatory exclusivity, subject to patent-term adjustments, patent-term extension, litigation outcomes, and the specific Orange Book entries for Ojjaara.
Composition and chemical-form patents
Earlier patent families cover momelotinib and related pyrimidine-based kinase inhibitor compounds. Later families cover specific salts, crystalline forms, pharmaceutical compositions, and manufacturing processes. Salt and solid-form claims can remain commercially relevant even when earlier compound claims approach expiration.
Method-of-use patents
Method-of-use protection is particularly important for Ojjaara because the product’s differentiation is tied to treatment of anemic myelofibrosis. Claims may address treatment of myelofibrosis, anemia, transfusion dependence, spleen symptoms, or dosing regimens.
Method claims are less valuable than a broad composition patent against an ordinary generic because a generic applicant may attempt a section viii carve-out from a patented indication. Their practical value increases when the branded label and treatment guidelines concentrate use in the protected population.
Orange Book status
Ojjaara is an FDA-approved small molecule and is eligible for Orange Book listing. A generic applicant would generally challenge listed patents through an Abbreviated New Drug Application and could file a Paragraph IV certification alleging that a listed patent is invalid, unenforceable, or not infringed.
No publicly established Paragraph IV litigation against Ojjaara was identified in the source set used for this analysis through mid-2024. The absence of an identified challenge does not remove future generic-entry risk. Generic companies normally assess market size before investing in a Paragraph IV case, and the timing of such a challenge depends on expected commercial value.
What generic entry risks exist for momelotinib?
Momelotinib has no biosimilar risk because it is a small molecule, not a biologic. The relevant threat is an ANDA-based generic.
Generic-entry risk is shaped by four factors:
| Risk factor |
Effect on Ojjaara |
| Patent expiry |
Determines the earliest routine generic launch date |
| Paragraph IV challenge |
Can accelerate litigation and create a launch opportunity before expiry |
| Formulation and salt protection |
May block simple substitution if valid and enforceable |
| Market size |
Determines whether a generic company can justify development and litigation costs |
A generic could target the active pharmaceutical ingredient and seek approval for non-protected indications through a label carve-out. GSK’s protection is stronger if the relevant Orange Book patents cover the active compound or a necessary salt or formulation rather than only a narrow anemia-related use.
The likely base case is continued branded exclusivity through the early 2030s, followed by rapid price erosion if multiple generic suppliers enter. The pace of erosion would depend on whether the product has become a standard second-line therapy and whether patients can be switched without clinical monitoring or specialist oversight.
Which companies are challenging momelotinib commercially?
The strongest current competitive pressure comes from companies selling alternative JAK inhibitors rather than from generic manufacturers.
Incyte
Incyte’s Jakafi is the principal incumbent. It has broad physician familiarity, long-term clinical use, and a large installed patient base. Its weakness is anemia, particularly in patients who develop or already have significant hemoglobin impairment.
Sobi and CTI BioPharma
Vonjo is positioned around myelofibrosis with severe thrombocytopenia. Its clinical niche differs from momelotinib’s anemia-focused positioning, but overlap exists in patients with cytopenias and advanced disease.
Bristol Myers Squibb
Inrebic competes directly in intermediate- and high-risk myelofibrosis. Commercial performance depends on its efficacy profile, tolerability, and use after or instead of ruxolitinib.
Emerging therapies
The pipeline includes investigational combinations involving BET inhibitors, LSD1 inhibitors, PI3K or AKT pathway agents, telomerase inhibitors, and novel anti-fibrotic therapies. These programs could pressure momelotinib if they improve survival, reverse fibrosis, or control symptoms without worsening cytopenias.
How strong is the momelotinib patent estate?
The patent estate is commercially meaningful but should not be treated as equivalent to a single, invulnerable composition-of-matter patent.
Its strengths are:
- Multiple patent families rather than one isolated filing.
- A differentiated clinical use in anemia-associated myelofibrosis.
- Protection covering the active ingredient, pharmaceutical forms, and therapeutic applications.
- A regulatory launch date that leaves meaningful commercial life before expected early-2030s patent expiry.
Its limitations are:
- Older compound patents may have less remaining term than newer formulation or use patents.
- Method-of-use claims can be vulnerable to label carving and non-infringement arguments.
- Generic applicants may challenge salt, crystalline-form, or formulation claims.
- The product’s addressable market is specialized, which can limit expected damages in litigation.
The estate is stronger for maintaining branded use through the core commercial period than for guaranteeing a long post-expiry monopoly.
What licensing deals affect momelotinib?
The critical transaction was GSK’s acquisition of Sierra Oncology. Sierra had licensed worldwide momelotinib rights from Gilead Sciences in 2018. GSK then obtained the asset through the Sierra acquisition rather than through a new direct product license.
The transaction path matters because it explains the asset’s valuation and ownership history:
| Party |
Role |
| Gilead Sciences |
Original developer and prior rights holder |
| Sierra Oncology |
Licensee and late-stage developer |
| GSK |
Current owner and commercial sponsor |
| FDA |
U.S. regulator |
| European Commission |
European Union marketing authorization authority |
No separate major co-commercialization agreement is central to the current commercial model. GSK controls global commercialization, subject to regional regulatory and reimbursement processes.
What revenue exposure does momelotinib create for GSK?
Momelotinib is strategically important but financially small relative to GSK’s largest products, including respiratory and infectious-disease franchises. Its value lies in portfolio diversification and the possibility of building a specialty hematology franchise.
The main revenue drivers are:
- U.S. patient uptake in newly diagnosed and previously treated myelofibrosis.
- Switching from ruxolitinib in patients with anemia.
- Reimbursement for a branded specialty drug.
- European launch execution.
- Treatment persistence and transfusion-independence benefits.
- Potential use in additional myelofibrosis subgroups, if supported by regulators.
The main downside risks are slower physician adoption, restrictive payer policies, limited diagnosis rates, competing JAK inhibitors, adverse-event concerns, and future combination therapies.
A $1 billion peak-sales outcome would require substantial penetration of the anemia-focused myelofibrosis population and durable treatment use. It should be viewed as a development-era commercial target rather than a reported financial result.
What is the likely market trajectory through patent expiry?
| Period |
Expected market dynamics |
| 2023-2024 |
U.S. launch, specialist education, formulary placement, early switching from incumbent JAK therapy |
| 2025-2027 |
International expansion, broader treatment sequencing, assessment of persistence and real-world anemia benefit |
| 2028-2030 |
Mature branded market, greater pressure from competing mechanisms and possible Paragraph IV activity |
| Early 2030s |
Expected patent-expiry window for key protection, subject to Orange Book status and litigation |
| Post-expiry |
Generic substitution, price erosion, and potential preservation of limited branded use through differentiated formulations or clinical positioning |
The most important near-term commercial question is whether physicians use momelotinib early in the treatment pathway or reserve it for patients who become anemic on ruxolitinib. Early-line adoption would materially expand revenue potential. A predominantly later-line role would support a narrower but clinically defensible market.
Key Takeaways
- Momelotinib dihydrochloride is marketed by GSK as Ojjaara for anemic intermediate- or high-risk myelofibrosis.
- Its main differentiation is ACVR1 inhibition and a clinical profile designed to address anemia, symptoms, and splenomegaly.
- GSK acquired Sierra Oncology for approximately $1.9 billion, making momelotinib a strategic specialty-hematology asset.
- The commercial opportunity is concentrated in patients with anemia, transfusion dependence, or inadequate tolerance of established JAK therapy.
- Ruxolitinib remains the main incumbent competitor; Vonjo and Inrebic compete in overlapping cytopenic or advanced-disease populations.
- Momelotinib faces generic rather than biosimilar risk.
- The patent estate likely supports branded commercialization into the early 2030s, subject to the specific Orange Book listings and litigation outcomes.
- No established Paragraph IV challenge was identified through mid-2024 in the reviewed public record.
- GSK’s $1 billion-plus peak-sales thesis remains dependent on market share, treatment sequencing, international reimbursement, and long-term use.
FAQs
Is momelotinib the same as Ojjaara?
Yes. Ojjaara is the GSK brand name for momelotinib dihydrochloride monohydrate tablets.
Does momelotinib compete directly with Jakafi?
Yes. Both drugs are JAK-pathway therapies for myelofibrosis. Momelotinib is differentiated by its anemia-focused clinical profile and ACVR1 inhibition.
Is momelotinib a biologic or a small molecule?
Momelotinib is an orally administered small-molecule kinase inhibitor. Future competition would come through generic applications, not biosimilar applications.
Who owns the momelotinib patent rights?
GSK is the current commercial owner after acquiring Sierra Oncology. Sierra had previously obtained worldwide rights from Gilead Sciences.
Could momelotinib receive additional indications?
Potential expansion would depend on clinical evidence and regulatory review. The most commercially relevant opportunities would involve additional myelofibrosis populations or earlier treatment use, but no unapproved indication should be treated as part of the current revenue base.
References
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GSK. (2022). GSK completes acquisition of Sierra Oncology. GSK plc.
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GSK. (2024). Annual report 2023. GSK plc.
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U.S. Food and Drug Administration. (2023). Ojjaara prescribing information. Center for Drug Evaluation and Research.
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U.S. Food and Drug Administration. (2023). FDA approves treatment for adults with myelofibrosis who have anemia. U.S. Department of Health and Human Services.
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Sierra Oncology. (2022). Sierra Oncology acquisition by GSK completed. Sierra Oncology, Inc.
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European Medicines Agency. (2024). Ojjaara: EPAR product information. European Medicines Agency.
