• The primary outcome will be to determine if sildenafil citrate is capable of alleviating pain in primary dysmenorrhea and total pain relief over 4 hours (TOPAR4), comparing a single dose of slidenafil 100 mg to a single dose of placebo. [ Time Frame: 4 hours ]
  

• Improvement in pain severity determined by visual analog scale results. [ Time Frame: 4 hours ]
  

It is well established that excess prostaglandin production in primary dysmenorrhea leads to ischemia of the uterine muscle, which consequently causes pelvic pain. A large number of drugs have been studied for pain relief in dysmenorrhea patients, with non-steroid anti-inflammatory drugs (NSAIDS) being the most effective with the overall success rate of more than 75%. Sildenafil citrate (Viagra) is an inhibitor that augments the vasodilatory effects of nitric oxide by preventing the degradation of cGMP in the uterine muscle. Sildenafil is commonly used in the treatment of male erectile dysfunction, pulmonary hypertension in children and adults, and in vitro fertilization. To date it has not been used in the treatment of primary dysmenorrhea.