Omjjara (Momelotinib)
JAK Inhibitor for Myelofibrosis with Anaemia
Quick Facts About Omjjara
Key Takeaways
- Omjjara is the first JAK inhibitor specifically approved for myelofibrosis patients with moderate to severe anaemia, addressing an important unmet medical need.
- Its unique triple mechanism (JAK1 + JAK2 + ACVR1 inhibition) reduces spleen size, improves constitutional symptoms, and combats anaemia by lowering hepcidin levels.
- The recommended dose is 200 mg once daily, taken with or without food. Dose reductions to 150 mg or 100 mg may be needed based on blood counts or side effects.
- Regular blood tests are essential during treatment to monitor platelet counts, white blood cells, and liver function.
- Omjjara must not be used during pregnancy or breastfeeding, and effective contraception is required during treatment and for at least one week after the last dose.
What Is Omjjara and What Is It Used For?
Omjjara contains the active substance momelotinib, a type of medicine known as a protein kinase inhibitor. It was developed specifically to address the needs of patients with myelofibrosis who experience significant anaemia – a population that was historically difficult to treat with existing JAK inhibitors. Momelotinib received approval from the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA) for this specific indication.
Myelofibrosis is a rare and serious myeloproliferative neoplasm (MPN) in which the bone marrow is gradually replaced by fibrous scar tissue. This disruption in normal bone marrow function leads to a cascade of clinical problems, including a dramatically enlarged spleen (splenomegaly), severe anaemia, fatigue, night sweats, bone pain, and unintentional weight loss. The disease affects approximately 1 to 2 people per 100,000 per year worldwide, with a median age at diagnosis of around 65 years.
Myelofibrosis can be classified as either primary myelofibrosis, which arises de novo without a preceding blood disorder, or secondary myelofibrosis, which develops as a progression from other myeloproliferative neoplasms. Secondary myelofibrosis includes post-polycythaemia vera myelofibrosis (arising from a condition that causes overproduction of red blood cells) and post-essential thrombocythaemia myelofibrosis (arising from a condition that causes overproduction of platelets).
How Omjjara Works
The pathophysiology of myelofibrosis involves dysregulated signalling through the JAK-STAT pathway, which leads to excessive production of pro-inflammatory cytokines, progressive bone marrow fibrosis, and extramedullary haematopoiesis (blood cell production outside the bone marrow, particularly in the spleen). This extramedullary haematopoiesis is the primary driver of splenomegaly in myelofibrosis.
Omjjara blocks the activity of specific enzymes called Janus-associated kinases (JAK1 and JAK2) and activin A receptor type 1 (ACVR1). By inhibiting JAK1 and JAK2, momelotinib reduces the overproduction of cytokines and decreases inflammation, thereby shrinking the enlarged spleen and alleviating constitutional symptoms such as fever, night sweats, bone pain, and weight loss.
What makes momelotinib distinct from other JAK inhibitors is its additional inhibition of ACVR1. This receptor plays a crucial role in regulating hepcidin, a hormone that controls iron metabolism. In myelofibrosis, hepcidin levels are often elevated, leading to iron restriction and worsening anaemia. By blocking ACVR1, momelotinib suppresses hepcidin production, thereby increasing iron availability for red blood cell production and improving anaemia. This dual benefit – reducing spleen size while simultaneously improving anaemia – addresses a critical gap in the treatment of myelofibrosis that previous JAK inhibitors could not adequately address.
What Should You Know Before Taking Omjjara?
Contraindications
You must not take Omjjara if you are allergic (hypersensitive) to momelotinib or any of the other ingredients in the tablets (listed in the composition section below). If you are unsure whether this applies to you, consult your doctor or pharmacist before taking Omjjara. The medication is also strictly contraindicated during pregnancy and breastfeeding due to the potential risk of harm to the baby.
Warnings and Precautions
Talk to your doctor, pharmacist, or nurse before starting Omjjara or during treatment if any of the following apply to you:
- Infections: If you have an active infection or frequently develop infections. Signs of infection may include fever, chills, cough, breathing difficulties, diarrhoea, vomiting, or pain or burning sensation during urination. Omjjara can lower your white blood cell count, making you more vulnerable to infections.
- Chronic hepatitis B: If you have a history of long-term hepatitis B infection, as it may become reactivated during treatment with Omjjara. Your doctor will test you for hepatitis B before starting treatment.
- Bleeding or bruising: If you experience unusual bleeding or bruising under the skin, prolonged bleeding after blood draws, or gum bleeding. These may be signs of low platelet counts (thrombocytopenia), a common side effect of Omjjara.
- Liver problems: If you have impaired liver function, your doctor may need to prescribe a lower dose of Omjjara and will monitor your liver function tests more frequently.
A class of medications similar to Omjjara (JAK inhibitors used for rheumatoid arthritis) has been associated with increased risks of certain serious conditions. Before or during treatment, discuss the following risk factors with your doctor:
- Age over 65: Patients aged 65 and older may have an increased risk of heart problems (including heart attack) and certain types of cancer.
- Cardiovascular disease: Current or past heart problems may increase the risk of major adverse cardiovascular events during JAK inhibitor treatment.
- History of cancer: Past or current malignancies should be discussed with your doctor.
- Smoking: Current or past smoking history is an additional cardiovascular risk factor.
- Blood clots (thrombosis): If you have a history of deep vein thrombosis (DVT) or pulmonary embolism (PE), or have risk factors for blood clots, such as recent major surgery, use of hormonal contraceptives or hormone replacement therapy, or a family history of clotting disorders.
Your doctor may recommend regular skin examinations while you are taking Omjjara, as JAK inhibitors have been associated with an increased risk of non-melanoma skin cancer. Report any new or changing skin lesions to your doctor promptly.
Blood Tests and Monitoring
Before and during treatment, your doctor will perform regular blood tests to monitor your blood cell counts (red blood cells, white blood cells, and platelets) and liver function. Based on these results, your doctor may adjust your dose or temporarily interrupt treatment. It is essential to attend all scheduled blood test appointments to ensure the safe and effective use of Omjjara.
Use in Children and Adolescents
Omjjara should not be given to children or adolescents under 18 years of age. This medication has not been studied in this age group, and its safety and efficacy in paediatric patients have not been established.
Pregnancy and Breastfeeding
Omjjara must not be taken during pregnancy. If you are pregnant, think you might be pregnant, or are planning to have a baby, do not take this medicine as it may harm the unborn child. Your doctor may ask you to take a pregnancy test before starting treatment to confirm that you are not pregnant.
If you are a woman of childbearing potential, you must use a highly effective method of contraception while taking Omjjara and for at least 1 week after the last dose. It is currently unknown whether Omjjara reduces the effectiveness of hormonal contraceptives. Therefore, it is recommended to also use a barrier method (such as a condom) during treatment and for at least 1 week after the last dose.
If you become pregnant while taking Omjjara, contact your doctor immediately.
Omjjara must not be used during breastfeeding. It is unknown whether the medication passes into breast milk, and a risk to the breastfed child cannot be excluded. Discuss with your doctor before taking this medicine if you are breastfeeding.
It is unknown whether Omjjara affects male or female fertility. Animal studies have shown effects on fertility. If you or your partner are planning to have a baby, consult your doctor before or during treatment.
Driving and Operating Machinery
Omjjara may cause side effects that affect your ability to drive or operate machinery safely. If you experience dizziness or blurred vision, do not drive or use machines until these symptoms have resolved. Consider these potential effects when deciding to perform activities requiring alertness and clear vision.
How Does Omjjara Interact with Other Drugs?
It is crucial to inform your doctor, pharmacist, or nurse about all medicines you are taking, have recently taken, or might take. This includes herbal remedies and over-the-counter medications. Omjjara can affect how some other medicines work, and other medicines can affect how Omjjara works. Drug interactions can change drug levels in the blood, either increasing the risk of side effects or reducing the therapeutic effect of the medication.
Drugs That May Increase Omjjara Side Effects
| Drug | Common Use | Interaction Type |
|---|---|---|
| Ciclosporin (cyclosporine) | Prevention of transplant rejection | May increase momelotinib blood levels |
Drugs That May Reduce Omjjara Effectiveness
Strong CYP3A4 enzyme inducers can accelerate the metabolism of momelotinib, reducing its blood levels and potentially decreasing its therapeutic effect. These medications should be used with caution or alternatives considered:
| Drug | Common Use | Mechanism |
|---|---|---|
| Carbamazepine | Epilepsy and seizure control | CYP3A4 induction |
| Phenobarbital | Epilepsy and seizure control | CYP3A4 induction |
| Phenytoin | Epilepsy and seizure control | CYP3A4 induction |
| St John's Wort (Hypericum perforatum) | Herbal remedy for depression | CYP3A4 induction |
Drugs Affected by Omjjara
Momelotinib may alter the blood levels of certain other medications by affecting drug transport proteins or metabolic enzymes. Your doctor may need to adjust the dose of these medications or monitor you more closely:
| Drug | Common Use | Effect |
|---|---|---|
| Rosuvastatin | Cholesterol lowering | Increased rosuvastatin levels |
| Sulfasalazine | Rheumatoid arthritis | Increased sulfasalazine levels |
| Metformin | Blood sugar control (diabetes) | Altered metformin levels |
| Theophylline | Breathing difficulties (asthma/COPD) | Altered theophylline levels |
| Tizanidine | Muscle spasticity | Increased tizanidine levels |
| Cyclophosphamide | Cancer treatment | Altered cyclophosphamide levels |
What Is the Correct Dosage of Omjjara?
Always take this medicine exactly as your doctor or pharmacist has told you. Check with your doctor or pharmacist if you are not sure. Omjjara is a long-term treatment and you should continue taking it for as long as your doctor advises. Your doctor will regularly monitor your condition to ensure the treatment is working as intended.
Adults
Standard Dosing
The recommended starting dose is 200 mg once daily, taken by mouth. Take Omjjara at the same time each day, with or without food. Swallow the tablet whole with water.
Dose Adjustments
Your doctor may recommend a lower starting dose if you have liver problems (hepatic impairment). During treatment, the dose may be reduced to 150 mg or 100 mg once daily, or treatment may be temporarily interrupted, depending on your blood test results and any side effects you experience, such as abnormal bleeding, bruising, diarrhoea, or nausea.
| Patient Group | Starting Dose | Notes |
|---|---|---|
| Adults (normal liver function) | 200 mg once daily | Standard recommended dose |
| Adults (hepatic impairment) | Reduced dose as determined by physician | Closer monitoring of liver function required |
| Children and adolescents (<18 years) | Not recommended | Safety and efficacy not established |
Children
Omjjara is not recommended for use in children and adolescents under 18 years of age. The safety and efficacy of momelotinib have not been studied in the paediatric population, and there is no relevant indication for its use in this age group as myelofibrosis is exceedingly rare in children.
Elderly Patients
No specific dose adjustment is required for elderly patients based on age alone. However, older patients may be more susceptible to certain side effects, including infections and thrombocytopenia, and your doctor will monitor you accordingly. As myelofibrosis predominantly affects older adults (median age at diagnosis approximately 65 years), extensive clinical experience exists with momelotinib in elderly patients.
Missed Dose
If you miss a dose of Omjjara, simply skip the missed dose and take your next dose at the regularly scheduled time the following day. Do not take a double dose to make up for a forgotten dose. Taking extra medicine will not improve your condition and may increase the risk of side effects.
Overdose
If you accidentally take more Omjjara than your doctor has prescribed, contact your doctor immediately or go to the nearest hospital emergency department. Take the medicine packaging with you so the healthcare team knows exactly what you have taken. Overdose symptoms may include an exaggeration of the known side effects, such as severe nausea, diarrhoea, dizziness, or abnormal blood counts.
What Are the Side Effects of Omjjara?
The side effects of Omjjara are classified by how frequently they occur. It is important to be aware of these potential effects and to discuss any concerns with your healthcare provider. Some side effects can be managed with dose adjustments, while others may require additional treatment or temporary interruption of Omjjara.
Serious Side Effects
Certain side effects can be serious and require immediate medical attention. Seek emergency care before taking your next scheduled dose if you experience any of the following:
- Infections – Signs include fever, chills, cough, difficulty breathing, diarrhoea, vomiting, or pain during urination. Infections can be serious in patients with reduced immune function.
- Low platelet count (thrombocytopenia) – May cause easy bruising, prolonged bleeding from cuts, or spontaneous bleeding. This is one of the most common serious side effects.
- Signs of blood clots – Sudden breathlessness, chest pain, leg swelling, or leg redness. These require emergency medical care.
Side Effects by Frequency
Very Common
May affect more than 1 in 10 people
- Infections (including respiratory and urinary tract infections)
- Low platelet count (thrombocytopenia)
- Dizziness
- Headache
- Cough
- Diarrhoea
- Nausea
- Abdominal pain
- Weakness (asthenia)
- Fatigue
Common
May affect up to 1 in 10 people
- Low white blood cell count (neutropenia) – may increase infection risk
- Vitamin B1 (thiamine) deficiency – may cause loss of appetite, listlessness, irritability
- Numbness, tingling, or weakness in arms, hands, legs, or feet (peripheral neuropathy)
- Abnormal tingling sensation (paraesthesia)
- Fainting (syncope)
- Spinning sensation (vertigo)
- Blurred vision
- Sudden flushing of the face, neck, or upper chest
- Localised bleeding under the skin (haematoma)
- Low blood pressure – may cause faintness when standing up
- Constipation
- Vomiting
- Skin rash (redness, swelling, or skin pain)
- Joint pain (arthralgia)
- Pain in arms, legs, hands, or feet
- Fever
- Elevated liver enzymes (ALT and AST) – may indicate liver problems
- Bruising
When to Contact Your Doctor
Contact your doctor, pharmacist, or nurse if any of the above side effects become severe or bothersome, or if you notice any side effects not listed here. It is particularly important to report any signs of infection, unusual bleeding or bruising, or symptoms that suggest blood clots (see warnings section above). Your doctor may adjust your dose or prescribe additional medications to help manage side effects.
How Should You Store Omjjara?
Keep this medicine out of the sight and reach of children at all times. Do not use this medicine after the expiry date stated on the bottle label and carton after "EXP". The expiry date refers to the last day of the stated month.
Omjjara should be stored in the original bottle to protect it from moisture. The bottle contains a desiccant (a small packet or canister that absorbs moisture) and a polyester coil – do not remove these from the bottle. Do not swallow the desiccant. There are no special temperature storage requirements, so the medicine can be kept at normal room temperature.
Do not throw away any medicines via wastewater or household waste. Ask your pharmacist how to dispose of medicines you no longer use. These measures help to protect the environment and ensure the safe disposal of potentially hazardous substances.
What Does Omjjara Contain?
Active Substance
The active substance in Omjjara is momelotinib, present as momelotinib dihydrochloride monohydrate. Each tablet contains the equivalent of 100 mg, 150 mg, or 200 mg of momelotinib.
Inactive Ingredients (Excipients)
Tablet core: Microcrystalline cellulose, lactose monohydrate, sodium starch glycolate (type A), magnesium stearate, colloidal anhydrous silica, and propyl gallate.
Film coating: Opadry II brown, containing polyvinyl alcohol, macrogols, titanium dioxide (E171), talc, yellow iron oxide (E172), and red iron oxide (E172).
Tablet Appearance and Packaging
| Strength | Shape | Colour | Markings |
|---|---|---|---|
| 100 mg | Round | Brown | Underlined "M" on one side, "100" on the other |
| 150 mg | Triangular | Brown | Underlined "M" on one side, "150" on the other |
| 200 mg | Capsule-shaped (oblong) | Brown | Underlined "M" on one side, "200" on the other |
Omjjara film-coated tablets are supplied in a white bottle with a tamper-evident seal and a child-resistant cap. Each bottle contains 30 tablets, a silica gel desiccant, a polyester coil, and is packaged in a cardboard carton.
Frequently Asked Questions About Omjjara
Omjjara is used to treat disease-related splenomegaly (enlarged spleen) and other symptoms in adult patients with myelofibrosis who have moderate to severe anaemia. Myelofibrosis is a rare blood cancer in which the bone marrow is replaced by scar tissue. This includes both primary myelofibrosis and secondary forms that develop from polycythaemia vera or essential thrombocythaemia. Omjjara is unique among JAK inhibitors because it also targets ACVR1, which helps improve anaemia – a common and debilitating feature of the disease.
While both Omjjara (momelotinib) and ruxolitinib inhibit JAK1 and JAK2, momelotinib has an additional mechanism of action: it also inhibits ACVR1 (activin A receptor type 1). This additional inhibition reduces hepcidin levels in the body, which improves iron metabolism and stimulates red blood cell production. As a result, Omjjara can help improve anaemia, whereas ruxolitinib often worsens it. This makes Omjjara particularly suitable for myelofibrosis patients with moderate to severe anaemia, including those who have become anaemic during prior JAK inhibitor therapy.
Yes, Omjjara can be taken with or without food. There are no specific dietary restrictions associated with the medication. The most important thing is to take it at the same time each day to maintain consistent blood levels. Swallow the tablet whole with a glass of water.
If you miss a dose, simply skip it and take your next dose at the scheduled time the following day. Do not take a double dose to compensate for a missed dose. Taking extra medicine will not improve your condition and may increase the risk of side effects. If you frequently forget doses, consider setting a daily alarm or using a pill organiser to help you remember.
Your doctor will perform regular blood tests before and during treatment to monitor your blood cell counts (including red blood cells, white blood cells, and platelets) and liver function (ALT and AST enzyme levels). These tests help detect potential complications early, such as thrombocytopenia (low platelets) or neutropenia (low white blood cells). Based on the results, your doctor may adjust your dose or temporarily interrupt treatment. Follow your doctor's schedule for blood tests closely.
No, Omjjara is not a cure for myelofibrosis. It is a treatment that helps manage the symptoms of the disease, including reducing spleen size, alleviating constitutional symptoms (such as fatigue, night sweats, and bone pain), and improving anaemia. The only potentially curative treatment for myelofibrosis is allogeneic stem cell transplantation, which is only suitable for a subset of patients. Omjjara is a long-term therapy that should be continued as long as your doctor recommends.
References
This article is based on the following peer-reviewed sources, regulatory documents, and international guidelines:
- European Medicines Agency (EMA). Omjjara (momelotinib) – Summary of Product Characteristics (SmPC). European public assessment report (EPAR). Available at: ema.europa.eu. Last updated 2025.
- U.S. Food and Drug Administration (FDA). Omjjara (momelotinib) – Prescribing Information. Approved September 2023.
- Verstovsek S, Gerber JM, Engelbrecht C, et al. MOMENTUM: momelotinib versus danazol in symptomatic and anaemic myelofibrosis patients previously treated with a JAK inhibitor. The Lancet. 2023;401(10373):269–280.
- Mesa RA, Kiladjian JJ, Catalano JV, et al. SIMPLIFY-1: A Phase III Randomized Trial of Momelotinib Versus Ruxolitinib in Janus Kinase Inhibitor–Naïve Patients With Myelofibrosis. Journal of Clinical Oncology. 2017;35(34):3844–3850.
- NCCN Clinical Practice Guidelines in Oncology: Myeloproliferative Neoplasms. National Comprehensive Cancer Network. Version 2.2025.
- Tefferi A. Primary myelofibrosis: 2023 update on diagnosis, risk-stratification and management. American Journal of Hematology. 2023;98(5):801–821.
- World Health Organization (WHO). WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. 5th edition. 2022.
- Harrison CN, Schaap N, Vannucchi AM, et al. Janus kinase-2 inhibitor fedratinib in patients with myelofibrosis previously treated with ruxolitinib (JAKARTA-2): a single-arm, open-label, non-randomised, phase 2, multicentre study. The Lancet Haematology. 2017;4(7):e317–e324.
Medical Editorial Team
This article has been written and reviewed by iMedic's medical editorial team, comprising board-certified specialists in haematology, oncology, and clinical pharmacology. Our team follows international guidelines from the EMA, FDA, WHO, and NCCN, applying the GRADE evidence framework to ensure the highest quality of medical information.
Conflict of Interest Statement: iMedic receives no commercial funding from pharmaceutical companies. All content is editorially independent. The medical editorial team has no financial relationships with the manufacturers of Omjjara or any competing products.