What the label lists and what reports show
Dimethyl fumarate side effects
Dimethyl fumarate's FDA label: “Most common adverse reactions (incidence ≥10% and ≥2% placebo) were flushing, abdominal pain, diarrhea, and nausea.” FAERS holds 122,284 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 (17,099 reports).
- Generic listed
Check it at the source: the dimethyl fumarate FDA label on DailyMed (effective July 29, 2025, Macleods Pharmaceuticals Limited); 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 dimethyl fumarate delayed-release capsules?Dimethyl fumarate delayed-release capsules may cause serious side effects including: allergic reaction (such as welts, hives, swelling of the face, lips, mouth or tongue, or difficulty breathing) PML a rare brain infection that usually leads to death or severe disability decreases in your white blood cell count Your doctor should do a blood test before you start treatment with dimethyl fumarate delayed-release capsules and while on therapy. liver problems. Your doctor should do blood tests to check your liver function before you start taking dimethyl fumarate delayed-release capsules and during treatment if needed. […]
Source: FDA drug label, Macleods Pharmaceuticals Limited, effective July 29, 2025 (SPL set f8ada3e3-55c0-43e3-95b9-c6d11ffc42dd), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (incidence ≥10% and ≥2% placebo) were flushing, abdominal pain, diarrhea, and nausea.
A table the label prints in its adverse reactions section without a title; its column headings name the groups compared
| Reaction | Dimethyl fumarate delayed-release capsules 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 ( 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 Reaction s [see Warnings and Precautions ( 5.7 )] Most common adverse reactions (incidence ≥10% and ≥2% placebo) were flushing, abdominal pain, diarrhea, and nausea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Macleods Pharma USA, Inc., at 1-888-943-3210 or 1-855-926- 3384 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. In placebo-controlled and uncontrolled clinical studies, a total of 2513 patients have received dimethyl fumarate delayed-release capsules and been followed for periods up to 13 years with an overall exposure of 11,318 person-years. …
Source: FDA drug label, Macleods Pharmaceuticals Limited, effective July 29, 2025 (SPL set f8ada3e3-55c0-43e3-95b9-c6d11ffc42dd), via openFDA; the full label on DailyMed
What do FAERS reports show?
122,284 reports list dimethyl fumarate among the medicines taken, each a report of something that happened, not proof the medicine caused it; 2,169 are coded as a death and 22,867 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, 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?
- Dimethyl 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