What the label lists and what reports show
Momelotinib side effects
Momelotinib's FDA label: “The most common adverse reactions (≥20% in either study) are thrombocytopenia, hemorrhage, bacterial infection, fatigue, dizziness, diarrhea, and nausea.” FAERS holds 1,339 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is thrombocytopenia (109 reports).
- No generic listed
Check it at the source: the momelotinib FDA label on DailyMed (effective July 20, 2026, GlaxoSmithKline LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of OJJAARA?OJJAARA may cause serious side effects, including: • Risk of Infections. People who take OJJAARA may develop serious infections that can lead to death, such as bacterial and viral infections, including COVID‑19. If you have an active infection, your healthcare provider should not start treatment with OJJAARA until your infection is gone. If you have had hepatitis B for a long time (chronic), OJJAARA may cause your hepatitis B to become active again. Your healthcare provider will monitor you and treat you for any infections that you get during treatment with OJJAARA. Tell your healthcare provider right away if you develop any of the following symptoms of infection: o fever o chills o cough o breathing problems o diarrhea o vomiting o pain or burning feeling when passing urine • Low platelet and white blood cell counts. […]
Source: FDA drug label, GlaxoSmithKline LLC, effective July 20, 2026 (SPL set 4a672fd1-eb7b-4aa9-9b23-845e4b5dc400), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (≥20% in either study) are thrombocytopenia, hemorrhage, bacterial infection, fatigue, dizziness, diarrhea, and nausea.
Table 3: Adverse Reactions Occurring in ≥5% of Anemic Patients Receiving OJJAARA during Randomized Treatment in SIMPLIFY-1
| Reaction | All Grades b % | Grade ≥3 % | All Grades % | Grade ≥3 % |
|---|---|---|---|---|
| Dizziness c | 24 | 1 | 15 | 2 |
| Fatigue c | 22 | 0 | 25 | 1 |
| Bacterial infection c,d | 21 | 8 | 12 | 2 |
| Hemorrhage c | 21 | 1 | 18 | 2 |
| Thrombocytopenia c | 21 | 11 | 34 | 6 |
| Diarrhea c | 20 | 1 | 20 | 1 |
| Nausea c | 20 | 0 | 3 | 1 |
| Abdominal pain c | 18 | 1 | 14 | 1 |
| Cough c | 14 | 0 | 11 | 0 |
| Hypotension c | 14 | 2 | 0 | 0 |
| Pain in extremity | 12 | 0 | 5 | 0 |
| Pyrexia c | 12 | 1 | 11 | 0 |
| Rash c | 12 | 0 | 3 | 0 |
| Renal and urinary tract infection c,d | 12 | 1 | 4 | 0 |
| Elevated liver enzymes c | 11 | 4 | 9 | 0 |
| Headache c | 11 | 0 | 16 | 0 |
| Peripheral edema | 11 | 0 | 8 | 0 |
| Arrhythmia c | 8 | 2 | 2 | 1 |
| Paresthesia c | 8 | 0 | 3 | 0 |
| Pneumonia c | 8 | 8 | 5 | 3 |
| Vomiting c | 8 | 0 | 5 | 0 |
| Back pain | 7 | 1 | 2 | 0 |
| Viral infection c,d | 6 | 0 | 13 | 2 |
| Vitamin B1 deficiency | 6 | 0 | 7 | 0 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following clinically significant adverse reactions are described elsewhere in the labeling: • Risk of Infections and Hepatitis B Reactivation [see Warnings and Precautions ( 5.1 )] • Thrombocytopenia and Neutropenia [see Warnings and Precautions ( 5.2 )] • Hepatotoxicity [see Warnings and Precautions ( 5.3 )] • Severe Cutaneous Adverse Reactions [see Warnings and Precautions ( 5.4 )] • Major Adverse Cardiovascular Events [see Warnings and Precautions ( 5.5 )] • Thrombosis [see Warnings and Precautions ( 5.6 )] • Malignancies [see Warnings and Precautions ( 5.7 )] • Symptom Exacerbation Following Interruption or Discontinuation of Treatment [see Warnings and Precautions ( 5.8 )] The most common adverse reactions (≥20% in either study) are thrombocytopenia, hemorrhage, bacterial infection, fatigue, dizziness, diarrhea, and nausea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact GlaxoSmithKline at 1-888-825-5249 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice. …
Source: FDA drug label, GlaxoSmithKline LLC, effective July 20, 2026 (SPL set 4a672fd1-eb7b-4aa9-9b23-845e4b5dc400), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,339 reports list momelotinib among the medicines taken, each a report of something that happened, not proof the medicine caused it; 208 are coded as a death and 303 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 19 reactions below, 10 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Momelotinib: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions