JAK1/JAK2 inhibitor

Jakafi (ruxolitinib)

Also marketed as Jakafi XR. An approved treatment for Chronic Graft-versus-Host Disease, Myelofibrosis and Polycythemia Vera.

FDA Approved (2021)by Incyte Corporation

Preclinical

Phase 1

Phase 2

Phase 3

Approved

2021

Drug facts

The same compound appears under different names depending on the context. Here is how to identify Ruxolitinib wherever you encounter it, plus the key facts at a glance.

Generic name: Ruxolitinib
Brand names: Jakafi, Jakafi XR
Development code: INCB018424
Drug class: JAK1/JAK2 inhibitor
Manufacturer: Incyte Corporation
How it's taken: Taken as an oral tablet, either Jakafi 10mg twice daily or the extended-release Jakafi XR 22mg once daily (approved May 2026).

An oral JAK1/JAK2 inhibitor approved for chronic graft-versus-host disease in adults and children 12 years and older after failure of one or two prior lines of systemic therapy.

In the REACH-3 trial, 70% of people on Jakafi responded by the start of the 7th treatment cycle, against 57% on other treatments their doctors chose, according to the FDA label.
Jakafi has also been FDA approved since November 2011 for adults with intermediate or high-risk myelofibrosis, including primary myelofibrosis and myelofibrosis that follows polycythemia vera or essential thrombocythemia.
In the COMFORT-I trial, 42% of people on Jakafi had their spleen shrink by at least 35% at week 24, compared with less than 1% on placebo, according to the FDA label.
Since December 2014, Jakafi has also been FDA approved for adults with polycythemia vera whose disease did not respond well enough to hydroxyurea or who could not tolerate it.
In the RESPONSE trial, 60% of people on Jakafi kept their hematocrit (the share of blood made of red cells) under control without needing blood removed at week 32, compared with 19% on other treatments, according to the FDA label.

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Where Ruxolitinib fits

For chronic GVHD, Jakafi is approved after 1 or 2 earlier systemic treatments, and other approved options include ibrutinib (2017), belumosudil (2021), and axatilimab (2024) for different lines of therapy.

For myelofibrosis, fedratinib (Inrebic), pacritinib (Vonjo) and momelotinib (Ojjaara) are also FDA approved, and no head-to-head trial has compared them with Jakafi.
For polycythemia vera, Jakafi is used after hydroxyurea has not worked well enough or could not be tolerated, and no head-to-head trial has compared it with the other approved polycythemia vera treatments.

How Ruxolitinib works

After a bone marrow or stem cell transplant, donor immune cells sometimes attack the recipient's tissues, causing chronic graft-versus-host disease. This immune attack is fueled by inflammatory signaling molecules (cytokines) that communicate through JAK1 and JAK2 proteins inside immune cells. Ruxolitinib blocks both JAK1 and JAK2, effectively turning down the volume on these inflammatory signals.

When JAK signaling is inhibited, several things happen: production of inflammatory cytokines decreases, activated immune cells calm down, and protective regulatory T cells (Tregs) expand. This rebalancing of the immune system helps reduce the attack on the patient's tissues while preserving some immune function against infections.

In the landmark REACH-3 trial, ruxolitinib produced responses in 70% of patients and delivered median failure-free survival of 38.4 months compared to just 5.7 months with best available therapy, establishing it as the standard second-line treatment for cGVHD.

Side effects and safety

What patients report

Blood counts are monitored regularly during treatment. The label also warns about serious infections (including tuberculosis, PML and hepatitis B flare-ups), flares of symptoms if treatment is stopped (seen mainly in myelofibrosis), non-melanoma skin cancer (regular skin checks), higher cholesterol, and, based on another JAK inhibitor, a higher risk of heart attack, stroke, blood clots, lymphoma and other cancers, especially in current or past smokers.

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 Ruxolitinib

Taken as an oral tablet, either Jakafi 10mg twice daily or the extended-release Jakafi XR 22mg once daily (approved May 2026). Treatment continues until cGVHD progression or unacceptable side effects. No food restrictions. Dose adjustments may be needed based on blood counts or drug interactions.

For myelofibrosis, the starting dose depends on the platelet count before treatment. It is 20mg twice daily (or Jakafi XR 44mg once daily) when platelets are above 200 x 10^9/L, 15mg twice daily (XR 33mg) from 100 to 200 x 10^9/L, and 5mg twice daily (XR 11mg) from 50 to under 100 x 10^9/L. Blood counts are checked every 2 to 4 weeks until the dose is stable, and the dose is lowered or paused when platelets or neutrophils fall.

The highest dose is 25mg twice daily (XR 55mg once daily), and the label says Jakafi should be stopped if the spleen has not shrunk and symptoms have not improved after 6 months.

For polycythemia vera, the starting dose is 10mg twice daily, or Jakafi XR 22mg once daily. The label lowers the dose when hemoglobin is 8 to under 10g/dL or platelets are 50 to under 75 x 10^9/L, and pauses treatment when hemoglobin is under 8g/dL, platelets are under 50 x 10^9/L or neutrophils are under 1 x 10^9/L. People with polycythemia vera and moderate or severe kidney problems start at 5mg twice daily (XR 11mg once daily).

Starting Jakafi? Your first 90 daysWhat happens before the first fill, the dose steps, the required tests and who to call, from the label and the drugmaker's own program.

Prescribing Jakafi? REMS, monitoring and prior authorization criteria for prescribers

Availability and cost

No generic available

Only available as the brand-name product.

Help paying for Jakafi

With private insurance, the drugmaker's copay card can lower what you pay for Jakafi. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE, but charity funds often can. Of the 10 charity funds for the conditions it treats, 5 were open on October 26, 2026. People on Medicare may still qualify for the drugmaker's free medicine program. Without insurance, you can apply to the drugmaker's free medicine program, which sets its own eligibility rules. Pick your insurance below to see which offers fit you.

Your insurance

From the drugmaker

Jakafi (Ruxolitinib)

IncyteCARES

Official program page Call 1-855-452-5234

Copay help
Eligible commercially insured patients may pay as little as $0 per month for Jakafi or Jakafi XR; annual benefit maximum applies. Government-insured and uninsured patients are not eligible.
For: private insurance · source
Free medicine program
Free Jakafi for uninsured patients, Medicare Part B/D/Advantage patients, or patients whose coverage was exhausted or denied, if they meet household income criteria.
For: no insurance, underinsured, Medicare · source
Bridge or quick-start supply
Free 30-day supply if commercial or exchange-plan coverage is delayed; proof of the insurance claim and delay is required.
For: private insurance · source
Other support
If not eligible for Incyte programs, IncyteCARES can share information on independent foundations that may help with drug, travel or lodging costs.
The official page does not say who qualifies. Ask the program. · source

Good to know: Patients in Alternate Funding Programs are not eligible for free drug. Phone line Mon-Fri 8 AM-8 PM ET.

Checked on the drugmaker's official pages on September 24, 2026. Programs change; confirm with the program before you rely on it.

Charity funds

From a charity · TotalAssist (formerly PAN Foundation)
Graft-vs-Host Disease (GVHD) fund
Open
Apply on the foundation’s page
Pays for: Out-of-pocket costs for approved medications, up to $9,500 per year. Requires health insurance (any kind).
From a charity · NMDP (formerly Be The Match / National Marrow Donor Program)
NMDP Patient Financial Assistance Grants fund
Apply directly
Apply on the foundation’s page
Pays for: Out-of-pocket costs before and after blood or marrow transplant, ongoing GVHD treatment costs, clinical-trial travel and financial-crisis grants.
The foundation says: “Status not shown on page”
From a charity · Blood Cancer United (formerly The Leukemia & Lymphoma Society)
Clinical Trials Co-Pay Fund (all blood cancers) fund
Open
Apply on the foundation’s page
Pays for: Insurance premiums and treatment-related copays, deductibles and coinsurance, up to $3,500 per year. Requires health insurance (any kind).
From a charity · Blood Cancer United (formerly The Leukemia & Lymphoma Society)
Patient Aid Program fund
Open
Apply on the foundation’s page
Pays for: One-time $100 stipend for non-medical expenses (transportation, food, housing, utilities); no income or insurance requirement, up to $100 per year.
The foundation says: “CURRENT FUND STATUS: Open. Fund is currently Open.”
From a charity · CancerCare Co-Payment Assistance Foundation
Myeloproliferative Neoplasms fund
Open
Apply on the foundation’s page
Pays for: Copays, coinsurance and deductibles for treatment, up to $7,000 per year. Requires Medicare, Medicaid or TRICARE.
The foundation says: “Status: Open. Grant Amount: $7,000 (Initial Grant Amount $7,000; Program CAP Amount $10,000)”
From a charity · TotalAssist (formerly PAN Foundation)
Myeloproliferative Neoplasms fund
Open
Apply on the foundation’s page
Pays for: Out-of-pocket costs for approved medications, up to $9,500 per year. Requires health insurance (any kind).
From a charity · The Assistance Fund
Myeloproliferative Neoplasms (MPN) fund
Waitlist
Apply on the foundation’s page
Pays for: Copays, coinsurance, deductibles and other health-related expenses.

Status as each foundation showed it on October 26, 2026.

Every program and charity fund for Chronic Graft-versus-Host Disease →

Every program and charity fund for Myelofibrosis →

Every program and charity fund for Polycythemia Vera →

More ways to get help paying for treatment →

Insurance said no? Your Insurer Denied a Rare Disease Drug and Fewer Than 1 in 100 People Appeal, So Here Is the Playbook · 14 min read

Ruxolitinib treatment timeline for Chronic Graft-Versus-Host Disease

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Answer the first 3 questions to see your plan.

Stage 1 of 5 · Start to 1 mo

Starting ruxolitinib

You are beginning ruxolitinib after your chronic GVHD did not respond well enough to corticosteroids. The usual starting dose is 10mg twice daily, though your transplant team may start lower if your blood counts are borderline. During this first month, your team will check your complete blood count every 2 to 4 weeks until your dose is stable, and will also monitor for viral reactivations: particularly cytomegalovirus (CMV), which can reactivate when JAK inhibitors further suppress your immune system. Your team may check CMV PCR levels regularly during the first few months. Ruxolitinib works by dialing down the overactive immune signaling (JAK1/JAK2 pathways) that drives GVHD, so you may notice some symptom improvement within the first few weeks, particularly in skin, mouth, or joint tightness. However, the full effect takes longer to develop. You are likely still on corticosteroids at this point. Your team will want to see a response before beginning any steroid taper. Some antifungals and antibiotics, such as fluconazole and voriconazole, can raise ruxolitinib levels. With fluconazole at 200mg a day or less, the cGVHD starting dose is lowered to 5mg twice daily, or 11mg once daily for Jakafi XR. Higher fluconazole doses should be avoided. Make sure your team knows all the medications you are taking.

Coming up

Over the next few weeks, your team will evaluate how your blood counts are holding up and whether your GVHD symptoms are starting to improve. If your counts drop significantly, your dose may be reduced temporarily. If you tolerate the drug well and symptoms are improving, your doctor may begin a slow steroid taper, typically reducing prednisone by about 10-20% every 1-2 weeks. If symptoms are unchanged after the first month, your team will likely continue at the current dose for a longer trial before making changes, since some patients take 2-3 months to respond. If you develop a serious infection or dangerously low counts, your team may pause ruxolitinib temporarily.

Get in touch with your transplant team if you notice

Fever, chills, or signs of infection: contact your transplant team immediately (post-transplant patients on JAK inhibitors are at increased infection risk, including CMV reactivation)
Unusual bruising, bleeding gums, or blood in stool (possible low platelet count)
Severe fatigue, dizziness, or shortness of breath at rest (possible severe anemia)
New or worsening skin rash, mouth sores, or eye dryness spreading rapidly (possible GVHD flare despite starting treatment)
Chest pain or irregular heartbeat

Questions to take to your next visit

What is my starting dose, and how will you decide whether to adjust it?
How often will I need blood count checks during the first few weeks?
Am I still at risk for CMV or other viral reactivations, and are you monitoring for that?
When can we start reducing my steroid dose?
What symptoms should make me call you right away versus waiting for my next appointment?
Are there medications or supplements I should avoid while on ruxolitinib?

See Chronic Graft-Versus-Host Disease trials enrolling now

Every stage of Ruxolitinib treatment at a glance

Starting ruxolitinib Start to 1 mo

Early response assessment 1 mo to 3 mo

You have been on ruxolitinib for 1-3 months and your transplant team is evaluating your initial response. In the REACH-3 trial, the overall response rate was 70%, meaning most patients showed at least some improvement in one or more organs. Your team is comparing your current organ scores (skin, mouth, eyes, joints, liver, lungs, GI tract) to where you started. If your symptoms have improved and your blood counts are stable, you may be in the early stages of a steroid taper. Some patients respond quickly within the first month, while others take longer. If your response has been partial so far, that does not mean the drug is failing. Partial responses can continue to deepen over the next several months. If you are not seeing any improvement at all, your team will discuss whether to continue longer, adjust the dose, or consider adding or switching to another agent.

If you are responding, the focus shifts to two goals: deepening the GVHD response and tapering steroids. In the final REACH-3 analysis, about 60% of people who responded to ruxolitinib were estimated to still be responding at 36 months. Your steroid taper will continue gradually. If you experience a GVHD flare during the taper, your team may temporarily increase the steroid dose while keeping ruxolitinib steady. For patients with no response after 3 months, your team will likely discuss second-line or third-line alternatives such as belumosudil, ibrutinib, or axatilimab. Once your dose is stable, blood counts are checked as your team decides. The label also advises a cholesterol check about 8 to 12 weeks after starting.

Formal response assessment 3 mo to 6 mo

This is the key decision window. Your transplant team now has enough data to classify your response. In clinical practice, doctors evaluate GVHD responses using the NIH organ scoring system, checking each affected organ on a 0-to-3 severity scale. If your scores have improved by at least one point in at least one organ without worsening in others, that counts as a partial response. If all involved organs have returned to a score of 0, you have a complete response. If scores are unchanged or worse, treatment is considered to have failed. Your team is also tracking whether you have been able to reduce your steroid dose. Successful steroid tapering to a low dose (typically 0.15mg/kg/day of prednisone or less) while maintaining GVHD control is one of the most important clinical outcomes.

For patients responding well: you will continue ruxolitinib and keep tapering steroids with a goal of eventually getting off corticosteroids entirely if possible. Monitoring frequency decreases to every 4-8 weeks. For patients with a partial response: your team may continue ruxolitinib longer, try a dose increase if tolerated, or discuss adding a second agent (belumosudil is the most common add-on). Combination approaches are being studied and some centers already use them. For patients with no response or worsening GVHD: your team will likely switch to a different mechanism such as belumosudil (a ROCK2 inhibitor), ibrutinib (a BTK inhibitor) or axatilimab (an anti-CSF-1R antibody, approved after at least 2 earlier treatments). Switching does not mean starting over: each agent targets a different pathway.

Stable treatment 6 mo to 18 mo

You have been on ruxolitinib for over 6 months and your GVHD is either well-controlled or you and your team have adjusted the treatment plan based on your response. If you are doing well, you may be on a reduced steroid dose or entirely off steroids. Your monitoring has become less frequent, typically every 2-3 months. Your transplant team is now focused on maintaining the response, managing any chronic side effects (particularly blood count changes), and screening for complications of both long-term immunosuppression and prior steroid use. In the final REACH-3 analysis, median failure-free survival was 38.4 months with ruxolitinib, compared with 5.7 months with other available treatments.

The label says a taper can be considered after 6 months of treatment for people who have responded and have stopped therapeutic doses of steroids. It lowers the dose by 1 step about every 8 weeks. Some patients stay on ruxolitinib indefinitely, particularly those with sclerotic or fibrotic disease that tends to relapse when immunosuppression is reduced. Others, especially those with an early complete response, may step down from 10mg twice daily to 5mg twice daily, then 5mg once daily, about 8 weeks apart. On Jakafi XR the step is from 22mg to 11mg once daily. A GVHD flare during taper is not uncommon. If it happens, your team will increase the dose back to the effective level and try again later. If you have been stable on a reduced dose for a long period, full discontinuation may eventually be attempted.

Long-term management 18 mo on

You are in the long-term phase of ruxolitinib treatment. By this point, your GVHD trajectory is well-established. You may still be on ruxolitinib at your maintenance dose, you may have successfully tapered to a lower dose, or you may have discontinued it entirely if your GVHD resolved. For patients who remain on treatment, monitoring typically occurs every 3-6 months with blood counts, liver function tests, and periodic organ-specific assessments. Long-term considerations now include monitoring for complications of prolonged immunosuppression (infections, secondary malignancies), managing any residual GVHD damage (dry eyes, sclerotic skin, restricted range of motion), and cancer surveillance.

If you have been stable for a year or more on a low dose, your team may attempt further tapering or discontinuation. Patients who have achieved a complete response sustained for at least 12 months have the best chance of successful discontinuation. If you are one of the patients who need to remain on ruxolitinib long-term due to persistent but controlled GVHD, long-term use has been studied, and your team will weigh the benefits against side effects over time. Your team will continue monitoring blood counts, infection risk, and cancer surveillance. The cGVHD treatment landscape continues to evolve, and newer agents or combinations may eventually offer additional options for further improving your quality of life.

This timeline shows typical patterns from the prescribing information, guidelines and published studies. Your own treatment may differ, and your transplant team is the source of truth for your plan. Last checked against the FDA label on November 7, 2026.

Sources

Clinical trial results

The Phase 3 REACH-3 trial randomized 329 patients with steroid-refractory or steroid-dependent cGVHD to ruxolitinib or best available therapy. Ruxolitinib achieved an overall response rate of 70% versus 57% for best available therapy. Median failure-free survival was 38.4 months versus 5.7 months (HR 0.36). The probability of sustained response at 36 months was 59.6% versus 26.7%. These results established ruxolitinib as the most effective proven option for steroid-refractory cGVHD.

In myelofibrosis, COMFORT-I (NCT00952289) randomized 309 adults with intermediate-2 or high-risk disease to Jakafi or placebo. At week 24, 42% on Jakafi had a spleen volume drop of 35% or more versus less than 1% on placebo, and 46% versus 5% had their symptom score cut at least in half. COMFORT-II (NCT00934544) randomized 219 adults 2:1 to Jakafi or the best available therapy their doctor chose, and at week 48, 29% on Jakafi reached a 35% spleen volume drop versus 0% on other therapy.

In COMFORT-I, low platelets were found in 70% on Jakafi versus 31% on placebo and anemia in 96% versus 87%, and the label calls these dose-related effects.

In polycythemia vera, RESPONSE (NCT01243944) randomized 222 adults with an enlarged spleen and a poor response to or intolerance of hydroxyurea to Jakafi or the best available therapy their doctor chose. At week 32, 23% on Jakafi met the combined goal of hematocrit control without blood removal plus a spleen volume drop of 35% or more, versus less than 1% on other therapy.

Complete hematologic remission, meaning controlled hematocrit, platelets and white cells, came in 24% versus 8%. Of the 25 people who met the combined goal at week 32, 19 still met it at week 80.

Development history

Ruxolitinib was developed by Incyte Corporation and first approved for myelofibrosis in 2011, followed by polycythemia vera. The recognition that JAK signaling drives GVHD pathology led to clinical development in transplant settings. FDA approved ruxolitinib for acute GVHD in May 2019 and for chronic GVHD in September 2021 based on the REACH-3 data. It also has indications for myelofibrosis and polycythemia vera.

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Common questions about Ruxolitinib

▸What is Ruxolitinib (Jakafi)?

An oral JAK1/JAK2 inhibitor approved for chronic graft-versus-host disease in adults and children 12 years and older after failure of one or two prior lines of systemic therapy. In the REACH-3 trial, 70% of people on Jakafi responded by the start of the 7th treatment cycle, against 57% on other treatments their doctors chose, according to the FDA label. Jakafi has also been FDA approved since November 2011 for adults with intermediate or high-risk myelofibrosis, including primary myelofibrosis and myelofibrosis that follows polycythemia vera or essential thrombocythemia. In the COMFORT-I trial, 42% of people on Jakafi had their spleen shrink by at least 35% at week 24, compared with less than 1% on placebo, according to the FDA label. Since December 2014, Jakafi has also been FDA approved for adults with polycythemia vera whose disease did not respond well enough to hydroxyurea or who could not tolerate it. In the RESPONSE trial, 60% of people on Jakafi kept their hematocrit (the share of blood made of red cells) under control without needing blood removed at week 32, compared with 19% on other treatments, according to the FDA label.

▸How does Ruxolitinib work?

When JAK signaling is inhibited, several things happen: production of inflammatory cytokines decreases, activated immune cells calm down, and protective regulatory T cells (Tregs) expand. This rebalancing of the immune system helps reduce the attack on the patient's tissues while preserving some immune function against infections.

▸What are the side effects of Ruxolitinib?

The most common side effects relate to blood count changes: anemia (low red blood cells), thrombocytopenia (low platelets), and neutropenia (low white blood cells). Infections including viral reactivations (particularly cytomegalovirus) require monitoring. Other common effects include fatigue, headache, diarrhea, nausea, and muscle spasms. Blood counts are monitored regularly during treatment. The label also warns about serious infections (including tuberculosis, PML and hepatitis B flare-ups), flares of symptoms if treatment is stopped (seen mainly in myelofibrosis), non-melanoma skin cancer (regular skin checks), higher cholesterol, and, based on another JAK inhibitor, a higher risk of heart attack, stroke, blood clots, lymphoma and other cancers, especially in current or past smokers.

▸How is Ruxolitinib taken?

▸Is Ruxolitinib FDA approved?

Yes, Ruxolitinib (Jakafi) is FDA approved (2021) for the treatment of Chronic Graft-versus-Host Disease and Myelofibrosis and Polycythemia Vera.

▸Is Jakafi approved for chronic GVHD?

Yes. Jakafi (ruxolitinib) was FDA-approved in September 2021 for chronic graft-versus-host disease in adults and children 12 years and older after failure of one or two prior lines of systemic therapy, based on the REACH-3 trial. ^[1]^[2]

▸How effective is ruxolitinib for chronic GVHD?

In the Phase 3 REACH-3 trial of 329 patients, ruxolitinib achieved a 70% response rate versus 57% with best available therapy, and median failure-free survival of 38.4 months compared to 5.7 months with best available therapy. The probability of sustained response at 36 months was 59.6% versus 26.7%. ^[2]

▸What are the side effects of Jakafi for chronic GVHD?

The most common side effects of Jakafi (ruxolitinib) are blood count changes, including anemia, low platelets, and low white blood cells, so blood counts are monitored regularly during treatment. Infections including cytomegalovirus reactivation require monitoring, and fatigue, headache, diarrhea, nausea, and muscle spasms are also common. The label also warns about serious infections such as tuberculosis and hepatitis B flare-ups, non-melanoma skin cancer, higher cholesterol, and, based on data from another JAK inhibitor, a higher risk of heart attack, stroke, blood clots, lymphoma, and other cancers, especially in current or past smokers. ^[1]

▸Is there a patient assistance program for Jakafi?

Yes. IncyteCARES offers copay assistance for commercially insured patients taking Jakafi (ruxolitinib), bringing the cost to as little as $0 per month, and provides free medication for eligible uninsured or underinsured patients. ^[3]

▸Is Jakafi approved for myelofibrosis?

Yes. The FDA approved Jakafi (ruxolitinib) on November 16, 2011 for adults with intermediate or high-risk myelofibrosis.^[5]

Types covered: Primary myelofibrosis and myelofibrosis that develops after polycythemia vera or essential thrombocythemia.^[4]

Once-daily form: Jakafi XR, an extended-release tablet taken once a day, was approved in May 2026 and carries the same uses.^[4]

Trial result: In COMFORT-I, 42% on Jakafi had their spleen shrink by at least 35% at week 24, versus less than 1% on placebo, and 46% versus 5% had their symptom score cut at least in half.^[4]

Source: Jakafi prescribing information, DailyMed, revised July 2026; Drugs@FDA NDA 202192

▸What is the starting dose of Jakafi for myelofibrosis?

The starting dose of Jakafi for myelofibrosis depends on the platelet count before treatment.^[4]

Platelets above 200 x 10^9/L: 20mg twice daily, or Jakafi XR 44mg once daily.

Platelets 100 to 200 x 10^9/L: 15mg twice daily, or Jakafi XR 33mg once daily.

Platelets 50 to under 100 x 10^9/L: 5mg twice daily, or Jakafi XR 11mg once daily.

Monitoring: Blood counts are checked every 2 to 4 weeks until the dose is stable, and the dose is lowered or paused if platelets or neutrophils fall.

When it stops: The label says to stop if the spleen has not shrunk and symptoms have not improved after 6 months.

Source: Jakafi prescribing information, DailyMed, revised July 2026

▸Is Jakafi approved for polycythemia vera?

Yes. Jakafi (ruxolitinib) has been FDA approved since December 2014 for adults with polycythemia vera who did not respond well enough to hydroxyurea or could not tolerate it.^[5]^[4]

Dose: The starting dose is 10mg twice daily, or Jakafi XR 22mg once daily.^[4]

Trial result: In RESPONSE, 60% on Jakafi had their hematocrit controlled without blood removal at week 32, versus 19% on other treatments, and 40% versus less than 1% had their spleen shrink by at least 35%.^[4]

Question for a doctor: Whether hydroxyurea has worked well enough is something to ask a hematologist.

Source: Jakafi prescribing information, DailyMed, revised July 2026; Drugs@FDA NDA 202192

▸What are the side effects of Jakafi for polycythemia vera?

In the RESPONSE trial, the most common problems on Jakafi were anemia and changes in blood counts and cholesterol.^[4]

Blood counts: Through week 32, anemia was found in 72% on Jakafi versus 58% on other treatments, and low platelets in 27% versus 24%.

Other effects: Diarrhea (15% vs 7%), dizziness (15% vs 13%), shortness of breath (13% vs 4%), muscle spasms (12% vs 5%) and shingles (6% vs 0%).

Cholesterol: High cholesterol showed up on lab tests in 35% versus 8%.

Stopping: Of people on Jakafi, 4% stopped because of side effects.

Label warnings: Serious infections, symptoms flaring if Jakafi is stopped, skin cancers other than melanoma, and higher risks of heart attack, stroke, blood clots and other cancers seen with another JAK inhibitor, especially in current or past smokers.

Source: Jakafi prescribing information, DailyMed, revised July 2026

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.

U.S. Food and Drug Administration · September 22, 2021. FDA approves ruxolitinib for chronic graft-versus-host disease. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-ruxolitinib-chronic-graft-versus-host-disease
New England Journal of Medicine. Ruxolitinib vs Best Available Therapy in Steroid-Refractory Chronic GVHD. https://www.nejm.org/doi/full/10.1056/NEJMoa2033122
Incyte Corporation. IncyteCARES for Jakafi. https://www.incytecares.com/oncology-hematology-jakafi/financial-assistance
U.S. National Library of Medicine, DailyMed · 2026-07. JAKAFI- ruxolitinib tablet; JAKAFI XR- ruxolitinib tablet, extended release. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f1c82580-87ae-11e0-bc84-0002a5d5c51b
U.S. Food and Drug Administration · 2011-11-16. Drugs@FDA: FDA-Approved Drugs. https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=202192
ClinicalTrials.gov. COntrolled MyeloFibrosis Study With ORal JAK Inhibitor Treatment: The COMFORT-I Trial. https://clinicaltrials.gov/study/NCT00952289
ClinicalTrials.gov. Controlled Myelofibrosis Study With Oral Janus-associated Kinase (JAK) Inhibitor Treatment-II: The COMFORT-II Trial. https://clinicaltrials.gov/study/NCT00934544
ClinicalTrials.gov. Study of Efficacy and Safety in Polycythemia Vera Subjects Who Are Resistant to or Intolerant of Hydroxyurea: JAK Inhibitor INC424 (INCB018424) Tablets Versus Best Available Care: (The RESPONSE Trial). https://clinicaltrials.gov/study/NCT01243944