The pivotal phase III trial using IFN-β1b was a randomized, double-blind, placebo-controlled, multicenter trial of 372 patients with RRMS over 2 years. This trial demonstrated a 34% reduction in overall relapses compared with placebo. More specifically, there was a 50% reduction in annualized relapses classified as moderate to severe in the treatment group. Patients receiving IFN-β1b were also found to have a lower T2 lesion volume and decreased accumulation of new lesions [IFNB Multiple Sclerosis Study Group. 1993]. Each of the IFN-β therapies, as well as glatiramer acetate, has been shown to delay conversion to CDMS in patients with CIS (Table 2). In the 5-year active treatment extension of the BENEFIT trial, the effects of early versus delayed treatment with IFN β1b were investigated. This study showed the risk of conversion to CDMS remained lower in the group receiving early treatment; 46% compared with 57% of patients converting from CIS to CDMS [hazard ratio (HR) 0.63; 95% confidence interval (CI) 0.48-0.83; log rank test p = 0.003) [Kappos et al. 2009].