Vaginal Sildenafil for Primary Dysmenorrhea

This phase 1 randomized, double-blind, placebo-controlled, two-period crossover trial will evaluate whether a single 100 mg vaginal sildenafil citrate suppository reduces uterine hypercontractility during menstruation in adults with moderate-to-severe dysmenorrhea. Uterine contractility will be measured using cine magnetic resonance imaging (MRI). Key secondary objectives are to evaluate acute menstrual pain reduction over 4 hours, characterize limited systemic exposure using a single 4-hour plasma sildenafil concentration, and assess short-term safety and tolerability.