Depression is a mental disorder, providing a major cause of morbidity worldwide. Several factors contribute to the development of depression. Regarding to the development of depression, many theories exist explaining the mechanisms from different point of views. The three most common treatments for depression are medication, psychotherapy and electroconvulsive therapy. Selective serotonin reuptake inhibitors are the primary medications prescribed, owing to their relatively mild side-effects, and because they are less toxic in overdose than other antidepressants. SSRIs are involved in many drug interactions with potentially serious clinical consequences. The clinical consequences of drug interactions with SSRI are either due to overdosing of the drug combined, or to a serotonin syndrome with neuromuscular and vegetative symptoms.