How long does depression last?
The average spell of clinical depression, if left entirely untreated, can last around 8 months. During a depression, the sufferer will normally be convinced that it will never go away, but this is a classic feature of the way depression makes us think.
Certain psychotherapies can actually worsen depression, which is why it is vital that you are well informed about depression treatment. Take a look at Which therapy is best for depression for more on this.
The right sort of psychotherapy can make a great difference very quickly. International guidelines for the treatment of depression state that a significant change should be seen within 6 sessions, or the patient should be referred elsewhere. Often, change is even quicker.