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Rituximab, a widely used off-label MS therapy, is associated with a significantly higher risk of inflammatory bowel disease (IBD) compared to other MS treatments, a large Swedish cohort study found. The crude IBD incidence rate was 110 per 100,000 person-years for rituximab versus just 13 for comparator drugs. Still, cumulative IBD incidence remained under 2% at 10 years, keeping the absolute risk in perspective.
Rituximab, the most commonly used MS therapy in Sweden, carries a notably higher risk of inflammatory bowel disease (IBD) compared to other disease-modifying treatments (DMTs), according to a large population-based cohort study published in JAMA Neurology and presented at MSToronto2026. Researchers analyzed over 13,700 therapy episodes from the Swedish MS register spanning 2011–2023, finding that IBD events were far more frequent in rituximab users — and that Crohn's disease made up 62% of those cases, versus just 29% in the general population.
That said, the absolute risk remains modest. Cumulative IBD incidence stayed below 2% at 10 years even for rituximab users, and the number needed to harm at 5 years was 131 — meaning one extra IBD case for every 131 patients treated with rituximab instead of a comparator DMT.
By the Numbers:
Why it matters: Clinicians prescribing anti-CD20 therapies for MS should counsel patients about GI symptoms and exercise extra caution in those with a prior IBD history. Researchers suspect this may be a class effect extending to ocrelizumab and ofatumumab.
