IRCT201705249014N164 IRCT 2017-06-08 Vice-chancellor for Research and Technology, Hamadan University of Medical Sciences Effect of omega-3-fatty acids versus placebo on clinical symptoms of patients with major depressive disorder Effect of omega-3-fatty acids versus placebo on clinical symptoms of patients with major depressive disorder: a double blind randomized clinical trial 2017-06-22 anticipated 60 Complete https://irct.ir/trial/9602 interventional Randomization: Randomized, Blinding: Double blinded, Placebo: Used, Assignment: Parallel, Purpose: Treatment, Other design features: Randomization: Random assignment of the patients to the intervention and control groups using random number table. Blinding: Patients will be unaware of the type of intervention. The physician who will examine the patients will not be aware of the intervention. Therefore, the trial will be run as double blind. 2 Major depressive disorder. Intervention 1: Intervention group: Routine treatment plus omega-3 capsule 100 mg daily for 12 weeks. Intervention 2: Control group: Routine treatment plus placebo capsule daily for 12 weeks.