What the label lists and what reports show
Diroximel fumarate side effects
Diroximel fumarate's FDA label: “Most common adverse reactions (incidence for dimethyl fumarate [which has the same active metabolite as VUMERITY] ≥10% and ≥2% more than placebo) were flushing, abdominal pain, diarrhea, and nausea.” FAERS holds 11,848 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 (1,611 reports).
- No generic listed
Check it at the source: the diroximel fumarate FDA label on DailyMed (effective May 29, 2025, Biogen Inc.); 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 VUMERITY?VUMERITY 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 VUMERITY 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. Tell your doctor right away if you get any of these symptoms of PML: weakness on one side of the body that gets worse vision problems confusion clumsiness in your arms or legs changes in thinking and memory personality changes herpes zoster infections (shingles), including central nervous system infections. other serious infections decreases in your white blood cell count. […]
Source: FDA drug label, Biogen Inc., effective May 29, 2025 (SPL set 2d74414f-6b83-4ea2-9a95-3cecabbce774), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (incidence for dimethyl fumarate [which has the same active metabolite as VUMERITY] ≥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 Reactions | 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 important adverse reactions are described elsewhere in labeling: Anaphylaxis and Angioedema [see Warnings and Precautions ( 5.1 )] Progressive Multifocal Leukoencephalopathy [see Warnings and Precautions Section ( 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 ( 5.6 )] Flushing [see Warnings and Precautions ( 5.6 )] Serious Gastrointestinal Reactions [see Warnings and Precautions ( 5.7 )] Most common adverse reactions (incidence for dimethyl fumarate [which has the same active metabolite as VUMERITY] ≥10% and ≥2% more than placebo) were flushing, abdominal pain, diarrhea, and nausea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Biogen at 1-800-456-2255 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 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 clinical practice. The data described in the following sections were obtained using dimethyl fumarate delayed-release capsules, which has the same active metabolite as VUMERITY.
Source: FDA drug label, Biogen Inc., effective May 29, 2025 (SPL set 2d74414f-6b83-4ea2-9a95-3cecabbce774), via openFDA; the full label on DailyMed
What do FAERS reports show?
11,848 reports list diroximel fumarate among the medicines taken, each a report of something that happened, not proof the medicine caused it; 354 are coded as a death and 2,305 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. Reports rose sharply in 2022 (2,568, against a median of 479 a year): FAERS counts follow reporting, which news, litigation and label changes can drive, not how often a reaction happens. Of the 21 reactions below, 6 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?
- Diroximel 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