To compare the efficacy of SMP-114 (120 and 240 mg/d) versus placebo in terms of the percentage of patients meeting the American College of Rheumatology criteria for 20% improvement in RA (ACR20) at week 24. The study hypothesis would be to demonstrate that the use of methotrexate and SMP-114 is more efficacious than Methotrexate alone.

Inclusion Criteria:

• Male or female patients aged at least 18 years, with RA for a minimum of 6 months
• Has been receiving methotrexate treatment (stable for 8 weeks)
• Has active disease classified as ACR functional class of I, II or III

Exclusion Criteria:

• Has previously discontinued DMARD therapy due to hepatic intolerance
• Has received any DMARD in addition to methotrexate during the 4 weeks prior to randomisation
• Is receiving more than 2 DMARDs in addition to methotrexate at the time of screening
• Is receiving or has received Gold, leflunomide or biological agents including TNF/IL-1 inhibitors within the 8 weeks prior to randomisation
• Has previously failed 2 or more DMARDS