Background Success of disease modifying therapy (DMT) for relapsing MS (RMS) is dependent on both effectiveness and adherence. We have explored reasons for stopping DMT in a large multicentre RMS cohort to inform disease management.

Methods Data was collected from sequential RMS patients receiving a DMT in 8 UK MS centres. DMT discontinuation events were recorded according to a standardised classification comprising: adverse event, increased risk of adverse event, lack of efficacy, onset of progressive disease, patient choice, pregnancy/pre-conceptual care, other, unknown.

Results Data from 6,816 prescriptions in 4,102 patients (female 72%, mean 1.7 prescriptions, range 1-6 per patient) were analysed. The most common reason for stopping was lack of efficacy (37%) followed by adverse event (31%), increased risk of adverse event (10%) and then pregnancy/preconceptual care (9%). Reasons for stopping varied by treatment duration, age, sex and DMT. DMT discontinuation due to adverse events fell from 51% in year 1, to 15% in years 5-10; discontinuation due to lack of efficacy rose from 22% to 45%. Increasing disability was rarely a reason to stop DMT.

Conclusions These data provide valuable insights into the real-world utility of MS DMTs and could provide a rationale to refine existing treatment pathways.