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It’s like a weight is pressing down on you. There are days when you just can’t get out of bed. You cannot face the world. You tell yourself simple things like: ‘Just get to the kitchen and get a glass of water’. But not being able to do something so basic is frightening.

Ian Thorpe, Australian swimmer and five-time Olympic gold medallist

Depression is a prevalent and debilitating psychiatric disorder. Its early age of onset and persistence combine to create substantial premature morbidity and mortality.1 Depression causes individual distress, functional, occupational and relationship impairment, reduced quality of life and societal economic cost.2

International prevalence of depression across lifetime and 1-year incidences for high-income countries are 14.6% and 5.5%, respectively. This compares to 11.1% and 5.9% in low- to middle-income countries.3 Globally, more than 350 million people suffer from depression, and it is predicted that by 2030 it will be the leading cause of disease burden (Fig. 21.1).4 The World Health Organization’s (WHO) global burden of disease report highlighted mental disorders specifically as being the leading cause of lost healthy years of living for females aged 15–44 years.4 Canadian studies have backed this finding, with the prevalence of major depressive disorder highest among females and younger age groups.5

Figure 21.1

Ten leading causes of burden of disease, world, 2004 and 2030



Depression can be subdivided into several different forms, some of which are specific to certain populations, age groups and areas of the world (e.g. seasonal affective disorder, SAD). This chapter will focus on the two primary forms of depression outlined below.

Major or unipolar depression

Unipolar depression is characterised by symptoms which persist for most of the day, nearly every day for at least two weeks. These symptoms may interfere with the person’s ability to work, sleep, study, eat or enjoy life. Episodes may be standalone and never reoccur, but more often, a person will experience several episodes over their lifetime.6

Bipolar depression or dysthymia

Depressive symptoms that last for longer than two years are classified as bipolar. A person diagnosed with this form of depression may have episodes of major depression along with periods of less severe symptoms.


Depression is associated with a range of symptoms, including low energy, lack of interest, low self-worth, and sometimes overwhelming feelings of sadness and anxiety. The current classification of depression is based on the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5®, 2013; Table 21.1), or ‘Recurrent depressive episodes’ in the International Classification of Diseases, 10th revision (ICD-10), classification of ...

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