A randomized trial evaluated the efficacy and safety of teriflunomide, an oral disease-modifying therapy for relapsing multiple sclerosis (MS). The study involved 1088 patients aged 18–55 years with MS, who were randomly assigned to receive placebo, 7 mg, or 14 mg of teriflunomide daily for 108 weeks. The primary endpoint was the annualized relapse rate, and the key secondary endpoint was confirmed disability progression over 12 weeks. Teriflunomide significantly reduced the annualized relapse rate compared to placebo, with relative risk reductions of 31.2% and 31.5% at 7 mg and 14 mg, respectively. The proportion of patients with confirmed disability progression was 27.3% with placebo, 21.7% with 7 mg teriflunomide, and 20.2% with 14 mg teriflunomide. Both doses of teriflunomide were superior to placebo on MRI-based measures of disease activity. Common adverse events included diarrhea, nausea, and hair thinning, with higher rates in teriflunomide groups. Elevated alanine aminotransferase levels were more common with teriflunomide than with placebo, but the incidence of levels three times the upper limit of the normal range was similar across groups. Serious infections occurred in 1.6–2.5% of patients, and no deaths were reported. Teriflunomide significantly reduced relapse rates, disability progression (especially at the higher dose), and MRI evidence of disease activity compared to placebo. The drug was well tolerated, with most adverse events being mild and not leading to discontinuation. The study demonstrated that teriflunomide is an effective and safe oral treatment for relapsing MS, with benefits comparable to existing injectable disease-modifying therapies. However, long-term safety data, including rare adverse events like progressive multifocal leukoencephalopathy, require further study. The findings support teriflunomide as a new oral monotherapy for relapsing MS.A randomized trial evaluated the efficacy and safety of teriflunomide, an oral disease-modifying therapy for relapsing multiple sclerosis (MS). The study involved 1088 patients aged 18–55 years with MS, who were randomly assigned to receive placebo, 7 mg, or 14 mg of teriflunomide daily for 108 weeks. The primary endpoint was the annualized relapse rate, and the key secondary endpoint was confirmed disability progression over 12 weeks. Teriflunomide significantly reduced the annualized relapse rate compared to placebo, with relative risk reductions of 31.2% and 31.5% at 7 mg and 14 mg, respectively. The proportion of patients with confirmed disability progression was 27.3% with placebo, 21.7% with 7 mg teriflunomide, and 20.2% with 14 mg teriflunomide. Both doses of teriflunomide were superior to placebo on MRI-based measures of disease activity. Common adverse events included diarrhea, nausea, and hair thinning, with higher rates in teriflunomide groups. Elevated alanine aminotransferase levels were more common with teriflunomide than with placebo, but the incidence of levels three times the upper limit of the normal range was similar across groups. Serious infections occurred in 1.6–2.5% of patients, and no deaths were reported. Teriflunomide significantly reduced relapse rates, disability progression (especially at the higher dose), and MRI evidence of disease activity compared to placebo. The drug was well tolerated, with most adverse events being mild and not leading to discontinuation. The study demonstrated that teriflunomide is an effective and safe oral treatment for relapsing MS, with benefits comparable to existing injectable disease-modifying therapies. However, long-term safety data, including rare adverse events like progressive multifocal leukoencephalopathy, require further study. The findings support teriflunomide as a new oral monotherapy for relapsing MS.