Thirteen girls received one tablet of montelukast ( Singulair , Merck , West Point , PA ) 10 mg daily starting on day 21 of the cycle until the last day of the menstrual period for two menstrual cycles , followed by one tablet of placebo ( Merck , West Point , PA ) daily starting on day 21 of the cycle until the last day of the menstrual period for two additional menstrual cycles .
