The purpose of this study is to determine whether milnacipran reduces widespread, non-joint pain in patients with rheumatoid arthritis (RA). The investigators will conduct a double-blind randomized crossover trial in subjects with RA to test the hypothesis that milnacipran improves widespread, non-joint pain. The investigators will also use data from the trial to determine whether response to milnacipran is associated with pain-modulating mechanisms from the central nervous system. The investigators hypothesize that response to milnacipran will be greater among patients with impaired central pain mechanisms than among patients with intact central pain modulating mechanisms.