BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) are established as treatment for managing pain associated with primary dysmenorrhea. However, the efficacy and tolerability of lumiracoxib 200 mg once daily (q.d.) has not previously been examined in primary dysmenorrhea. METHODS: Two randomized, multicenter, double-blind, placebo-controlled, crossover studies of similar design have assessed the efficacy and tolerability of two regimens of lumiracoxib compared with placebo (Study 1) or naproxen and placebo (Study 2) in women (aged 18-45 years) with moderate to severe primary dysmenorrhea. In Study 1 (n = 132), patients received lumiracoxib 200 mg q.d., lumiracoxib 200 mg with a 200 mg redose (p.r.n.) on day 1, or placebo. In Study 2 (n = 144), patients received lumiracoxib 200 mg q.d., lumiracoxib 200 mg with a 200 mg redose p.r.n. on day 1, naproxen 500 mg twice daily (b.i.d.), or placebo. Patients recorded study medication use, efficacy assessments, and rescue medication use. RESULTS: The primary efficacy variable, summed (time-weighted) pain intensity difference (categorical scale) over the first 8 hours (SPID-8), was similar between all active treatments (e.g., p = 0.939 for naproxen 500 mg b.i.d. vs. lumiracoxib 200 mg q.d. in Study 2), and all active treatments were superior to placebo (p < 0.001). Median time-to-onset of analgesia was similar between lumiracoxib 200 mg q.d. and naproxen 500 mg b.i.d. Similar trends were observed for all other secondary efficacy variables. All treatments were well tolerated. CONCLUSIONS: Short-term administration of lumiracoxib 200 mg q.d. is effective and well tolerated and provides an alternative treatment option for the management of moderate to severe pain associated with primary dysmenorrhea.