Depressive disorders often appear in recurrent episodes or in phases, with a high rate of recurrence in untreated individuals. Under adequate, multi-stage treatment can about 2/3 of all outpatients with major depression achieve long term remission (cf. Rush 2006).
The risk of recurrence or relapse is particularly enhanced if the victims suffer from bipolar affective disorder, double depression or comorbid anxiety disorders or addiction problems, if the disease first appeared at a very early age and / or if the patients responded badly on the previous therapy (cf. Rush 2006).
The duration of depressive episodes can vary from a few weeks to long episodes of more than one year in duration. Untreated, the episode duration is on average about 6 to 8 months.
About two thirds of the affected premenopausal women report premenstrual worsening of their depressive symptoms (cf. Kornstein 2005).
The risk for a severe course of depression increases with advanced age and in unfavorable family and social conditions such as lack of support and continuous problems and conflicts. A genetic load with multiple diseased blood relatives also increases the risk for a severe course.
In addition the existence of other diseases, such as an obsessive-compulsive disorder, eating disorder, post traumatic stress disorder or an alcohol or drug dependency may complicate the course of depression. Certain personality styles, such as histrionic or narcissistic personality disorders may complicate the course.
There are studies that suggest a link between genetic variations in the serotonin 2A receptor and the success of treatment with SSRIs (cf. McMahon 2006).