Depression is a common disorder related to other psychiatric and somatic diseases, and it often complicates the diagnosis and treatment. According to various studies 20-60% of patients with general medical conditions have symptoms of depression and 15-45% fulfil the criteria of a mood disorder. Remember somatic diseases that may cause depression (table ). Rule out possible drugs and narcotic substances that may cause mood disorders (table ). The role of somatic differential diagnosis is especially emphasized: in elderly patients with no previous mood disorders in patients with atypical symptoms of depression in patients who do not benefit from traditional treatment of depression In a patient with somatic disease it is not always easy to differentiate the somatic symptoms from those of depression. A somatic disease may contribute to the development of depression both through a direct physiological and an indirect psychological reaction formation. The potential interactions with the medications used for somatic diseases should be taken into account when starting drug treatment for depression.