Objectives: Many women experience menstrual cramps, which adversely affects quality-of-life. Both naproxen and acetaminophen are indicated to relieve menstrual pain. This study assessed the analgesic efficacy of a single, maximum non-prescription dose of naproxen sodium compared with that of acetaminophen in the treatment of primary dysmenorrhea.Methods: Healthy females with primary dysmenorrhea were included in our double-blind, randomized, crossover study (trial registration no. NCT03448536). When pain was moderate (≥5 on 0-10 numerical rating scale), subjects took a single dose of naproxen sodium (440 mg) and crossed over to acetaminophen (1000 mg) in the next cycle, or vice versa. Total pain relief over 12 h (TOTPAR0-12) was the primary outcome, while secondary outcomes included summed pain intensity differences (SPID) and TOTPAR scores throughout 12 h, and subject overall evaluation of treatment.Results: The per protocol population (n = 189) used naproxen sodium (n = 170) and acetaminophen (n = 160). TOTPAR0-12 was significantly greater with naproxen sodium than acetaminophen (least-squares (LS) mean difference = 4.31; p < .001), and pain intensity was significantly lower (SPID0-12 LS mean difference = 9.80; p < .001). Some measures of pain intensity favoring naproxen sodium became significant at earlier time points (e.g. SPID4-6 LS mean difference = 1.49; p = .02). After 6 h post-dose, naproxen sodium was significantly more effective than acetaminophen, maintained for 12 h (SPID6-12 LS mean difference = 8.27; TOTPAR6-12 LS mean difference = 3.75; both p < .001). Significantly more subjects rated naproxen sodium as good-to-excellent (70.6%) vs acetaminophen (63.1%) (p = .002).Conclusions: A single, maximum non-prescription dose of naproxen sodium was more effective than acetaminophen over 12 h.

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