Major Depressive Disorder

Major Depressive Disorder

Major depressive disorder (clinical depression/major depression/etc) is a mental disorder characterised by an overwhelming, all-encompassing depressed mood, and a loss of pleasure/interest in normally enjoyable activities.

MDD is characterised by the experiencing of either a Single MDE or Recurrent MDEs.

Major Depressive Episode Classification

Major depressive episodes refer to a cluster of symptoms of Major Depressive Disorder. It differs from normal unhappiness in severity (5/9 symptoms), long lastingness and level of impairment.

The criterion for classification is experiencing over a 2 week period -

  • The following 2:
    • Depressed mood
    • Loss of pleasure/interest
  • and 3+ more of these:
    • Weight loss/gain
    • Insomnia/Hypersomnia
    • Psychomotor Agitation/Retardation
    • Fatigue
    • Feelings of worthlessness/guilt
    • Diminished ability to concentrate/Indecisiveness
    • Suicidal intent/thoughts of death

An MDE typically lasts 4-9 months untreated.

Recurrent MDEs

  • Recurrent episodes are common
  • ~50% of MDE sufferers have a 2nd MDE
  • 70% of 2nd MDE sufferers have a 3rd MDE
  • 90% of 3rd MDE sufferers have a 4th MDE


Similarly to any of the other causal models of mental disorders, there are biological explanations and psychological explanations and biological+psychological explanations (e.g.).

Psychological Influences: Controllability

Learned Helplessness Theory of depresssion is the view that clinical depression is caused by people learning that they have no control over the negative events in their life.

LH and Cognitive Theory

Not all dogs exposed to uncontrollable shock developed LH. Perhaps because of the belief aspect - without irrational maladaptive thought processes, depression will not develop.

Cognitive Theories of Depression

Cognitive Therapy believes mental disorders are underpinned by irrational and maladaptive beliefs.


  • Anxiety and Depression:
    • “I absolutely MUST, at all times, perform well and win the approval of significant others. If I fail, that is awful and I am a bad, incompetent, unworthy person, who will probably always fail and deserves to suffer”."
  • Anger and Vindictiveness:
    • “Other people with whom I relate absolutely MUST, at all times, treat me nicely, considerately and fairly. Otherwise, it is terrible and they are rotten, bad, unworthy people who do not deserve a good life”
  • Self Pity/Anger/Depression
    • “The conditions under which I live absolutely MUST be favorable, safe, hassle-free, and quickly and easily enjoyableif they are not that way it's awful and horrible and I can't bear it and my life is impossible and hardly worth living”


  • Biological
    • Pharmacological - SSRIs, tricyclics
    • Electro-Chemical Therapy
    • Home Remedies
  • Cognitive-Behavioural Therapy
    • Modifying Behaviours
    • Challenging Behaviours
  • Interpersonal Therapy
    • Focusses on identifying and resolving social/interpersonal triggers
      • Unresolved grief
      • Role disputes
      • Role transitions
      • Interpersonal deficits


MDD has an average lifetime prevalence (proportion of people who've ever suffered) of 15-20%, and a point prevalence of 5-9% (proportion of people currently suffering).

  • This rate varies across cultures
  • Females are ~twice as likely to suffer MDD as men (reasons why are unknown)
  • Mean age of onset is ~30 years.



  • Leading cause of medical disability for 14-44y/olds (Ricci et al, 2003)
  • 3rd largest burden of disease worldwide (2004 WHO). (estimated to reach 1st by 2030)
  • Australian Economics;
    • Costs $14.9 billion annually
    • More than 6 million working days lost each year
  • Social Costs
    • Social isolation
    • Lower probability of getting married
    • Lower educational attainment
    • Lower incomes
    • 5x as likely to be substance abusers
  • Suicide Risk
    • 15% of untreated MDD sufferers commit suicide
    • 66% of people who commit suicide are MDD sufferers


Dysthymic Disorder

Dysthymic Disorder is a milder, more chronic version of MDE.


  • Persistently mild/moderate depressed mood that continues for 2+ years
  • Milder than major depression
  • Can persist unchanged over long periods (e.g. 20+ years)
  • Can combine with DDM to create Double Depression.