What the label lists and what reports show
Monomethyl fumarate side effects
Monomethyl fumarate's FDA label: “Most common adverse reactions (incidence for dimethyl fumarate [the prodrug of BAFIERTAM] ≥10% and ≥2% more than placebo) were flushing, abdominal pain, diarrhea, and nausea.” FAERS holds 926 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 flushing (348 reports).
- No generic listed
Check it at the source: the monomethyl fumarate FDA label on DailyMed (effective July 16, 2026, Banner Life Sciences 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 BAFIERTAM?BAFIERTAM may cause serious side effects including: allergic reaction (such as welts, hives, swelling of the face, lips, mouth or tongue, or difficulty breathing). Stop taking BAFIERTAM and get emergency medical help right away if you get any of these symptoms. PML (progressive multifocal leukoencephalopathy), a rare brain infection that usually leads to death or severe disability over a period of weeks or months. […]
Source: FDA drug label, Banner Life Sciences LLC, effective July 16, 2026 (SPL set a161f9d4-70f1-4097-957a-eafb35d3274f), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (incidence for dimethyl fumarate [the prodrug of BAFIERTAM] ≥10% and ≥2% more than placebo) were flushing, abdominal pain, diarrhea, and nausea.
Table 1: Adverse Reactions in Study 1 and 2 Reported for Dimethyl Fumarate at ≥ 2% Higher Incidence than Placebo
| Adverse Reaction | Dimethyl Fumarate 240 mg Twice Daily N=769 (%) | Placebo N=771 (%) |
|---|---|---|
| Flushing | 40 | 6 |
| Abdominal pain | 18 | 10 |
| Diarrhea | 14 | 11 |
| Nausea | 12 | 9 |
| Vomiting | 9 | 5 |
| Pruritus | 8 | 4 |
| Rash | 8 | 3 |
| Albumin urine present | 6 | 4 |
| Erythema | 5 | 1 |
| Dyspepsia | 5 | 3 |
| Aspartate aminotransferase increased | 4 | 2 |
| Lymphopenia | 2 | <1 |
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: Anaphylaxis and Angioedema [see Warnings and Precautions ( 5.1 )] Progressive Multifocal Leukoencephalopathy [see Warnings and Precautions ( 5.2 ) ] Herpes Zoster and Other Serious Opportunistic Infections [see Warnings and Precautions ( 5.3 ) ] Lymphopenia [see Warnings and Precautions ( 5.4 )] Liver Injury [see Warnings and Precautions ( 5.5 )] Flushing [see Warnings and Precautions ( 5.6 )] Serious Gastrointestinal Reactions [see Warnings and Precautions ( 5.7 )] Most common adverse reactions (incidence for dimethyl fumarate [the prodrug of BAFIERTAM] ≥10% and ≥2% more than placebo) were flushing, abdominal pain, diarrhea, and nausea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Banner Life Sciences at toll-free phone: 1-866-MMF- 95MG 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 to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The data described in the following sections were obtained using dimethyl fumarate delayed-release capsules (the prodrug of BAFIERTAM). …
Source: FDA drug label, Banner Life Sciences LLC, effective July 16, 2026 (SPL set a161f9d4-70f1-4097-957a-eafb35d3274f), via openFDA; the full label on DailyMed
What do FAERS reports show?
926 reports list monomethyl fumarate among the medicines taken, each a report of something that happened, not proof the medicine caused it; 3 are coded as a death and 48 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 23 reactions below, 8 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?
- Monomethyl fumarate: 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