The aim of this double-blind, randomized, clinical trial study, is to assess the effect of Stimol (Citrulline Malate) on Sexual Dysfunction in Multiple Sclerosis patients. In this study, 50 patients with multiple sclerosis, who suffering from sexual dysfunction refer to the Zanjan neurology clinic are recruited.Patients will rule out for anatomical sexual dysfunction. also patients with Pregnancy and breast feeding will be excluded. For all patients sexual dysfunction standard questionnaire will be completed. Then they are randomly assigned to two 25-member groups.The first group will take 1gram citrulline malate oral solution 3 times a day for 30 days, and the second group will take placebo. After 30 days, for all the participants the questionnaires will be completed again and results will analyzed.