Understanding most common side effects

It’s important to talk with your healthcare provider about the most common side effects of VUMERITY® (diroximel fumarate). Flushing and stomach problems are the most common reactions, especially at the start of therapy, and may decrease over time. Read more about them below.


Symptoms are usually described as redness, itching, or rash.

Stomach problems

Symptoms include nausea, vomiting, diarrhea, stomach pain, or indigestion. Stomach problems occurred most frequently in the first month and lessened thereafter. Some gastrointestinal problems can be serious. Get more information about serious side effects.

In a 96 week study, about 30% of the people experienced stomach problems, but they resolved in 89% of those people. Many experienced them within the first month and on average, they lasted about a week.*

*60% of people with stomach problems experienced them within the first month of treatment, which generally lasted 7.5 days.

Call your healthcare provider if you have any of these symptoms and they bother you or do not go away.

A separate analysis of stomach problems: VUMERITY compared with dimethyl fumarate

In a small 5-week study, people with relapsing MS were asked to track any stomach problems. 253 people took VUMERITY and 249 people took dimethyl fumarate.

Limitations to keep in mind

For this study, people rated the severity of their stomach issues on a scale of 0 (no issue) to 10 (extreme). Keep in mind, it can be hard to compare stomach problems. People had to report their own symptoms, and there's no widely used scale. This analysis was not planned as part of the clinical trials, so the data may not be as reliable. This data is not included in the full Prescribing Information for VUMERITY. Additional studies may be needed to confirm these findings.

More days without stomach problems

People taking VUMERITY reported 46% fewer days with stomach problems that they rated ≥2 than people taking dimethyl fumarate, and their stomach problems were generally less severe.

(1.4 days compared with 2.6 days for people taking dimethyl fumarate.)

More people stayed on VUMERITY

People were 83% less likely to stop taking VUMERITY because of stomach problems than dimethyl fumarate.

(0.8% of those taking VUMERITY stopped treatment compared with 4.8% of those taking dimethyl fumarate.)

In week 1, people taking VUMERITY received the starter dose (231-mg pill) and a placebo pill twice a day. In weeks 2-5, they received the regular dose (two 231-mg pills) twice a day. In week 1, people taking dimethyl fumarate received the starter dose (120-mg pill) and one placebo pill twice a day. In weeks 2-5, they received the regular dose (240-mg pill) and one placebo twice a day.