IRCT20120215009014N311 IRCT 2019-10-21 Hamedan University of Medical Sciences Effect mirtazapine versus placebo on the treatment of irritable bowel syndrome associated with diarrhea Effect mirtazapine versus placebo on the treatment of irritable bowel syndrome associated with diarrhea: a double-blind randomized clinical trial 2019-11-22 anticipated 50 Complete https://irct.ir/trial/42843 interventional Randomization: Randomized, Blinding: Double blinded, Placebo: Used, Assignment: Parallel, Purpose: Treatment, Randomization description: The patients will be randomly assigned to intervention and control groups using block randomization. For this purpose, we will prepare four sheets of paper, writing on two sheets the name of the intervention and on the other two sheets the name of the control. The paper sheets will be pooled, placed in a container, and randomly drawn one at a time for each patient without replacement until all four sheets are drawn. The four paper sheets will be then placed back into the container, and this action repeated until the sample size is reached, Blinding description: The shape of the medications and placebos will be perfectly the same. Therefore, patients will be unaware of the type of intervention. The physician who will examine the patients will not be aware of the intervention. Thus, the trial will be run as double-blind. 3 Irritable bowel syndrome with diarrhea. Intervention 1: Intervention group: Routine treatment plus mirtazapine tablets 15 mg every night for one week and then 30 mg every night for 6 weeks. Intervention 2: Control group: Routine treatment plus placebo tablets every night for 7 weeks. Undecided - It is not yet known if there will be a plan to make this available Justification or reason for indecision in sharing IPD is It depends on the situations and the results of the study as well as approval of the financial supporting organization.