Public Health Agency of Canada
Symbol of the Government of Canada

Share this page

What is Depression?

Everybody goes through "ups and downs" in their lives. Sometimes we use the term "depression", or "depressed" to describe these everyday feelings.

But the normal experiences of life shouldn't be confused with the serious medical illnesses known as mood disorders. There are different kinds of depressive mood disorders, including bipolar disorder (manic-depressive illness), post-partum depression and psychosis, but clinical depression, or "unipolar disorder" is the most common depressive disorder.

Mood disorders are very real illnesses that can have serious and sometimes fatal results. They affect the entire body and not just the mind. Their physical symptoms can range from fatigue to stomach complaints or muscle and joint pain. Many people never realize that they are suffering from depression.

Mood disorders are one of the most common mental illnesses in the general population. According to Statistics Canada's 2002 Mental Health and Well-being Survey Canadian Community Health Survey (CCHS), Cycle 1.2), 5.3% of the Canadian population aged 15 years and over reported symptoms that met the criteria for a mood disorder in the previous 12 months, including 4.8% for major depression and 1.0% for bipolar disorder.

Further, one in 7 adults (13.4%) identified symptoms that met the criteria for a mood disorder at some point during their lifetime, including 12.2% for depression and 2.4% for bipolar disorder.1

Studies have consistently documented higher rates of depression among women than among men: the female-to-male ratio averages 2:1.2

What Causes Mood Disorders?

Mood disorders have no single cause, but several risk factors interact to produce the clinical symptoms of the various mood disorders. Individuals with depression and bipolar disorder often find a history of these disorders among immediate family members.3, 4 Many different genes may act together and in combination with other factors to cause a mood disorder. Research is getting closer to identifying the specific genes that contribute to depression.

One episode of major depression is a strong predictor of future episodes. More than 50% of individuals who have an episode of major depression experience a recurrence.3 Traditionally, stress has been viewed as a major risk factor for depression. Recent research suggests that stress may only predispose individuals for an initial episode, but not for recurring episodes.5 Some individuals are more susceptible than others to depression following traumatic life vents, when in difficult or abusive relationships, or as a result of socio-economic factors such as income, housing, prejudice and workplace stress. A strong association exists between various chronic medical conditions and an increased prevalence of major depression.6 Several chronic medical conditions, such as stroke and heart disease, obesity, Parkinson's disease, epilepsy, arthritis, cancer, AIDS, chronic obstructive pulmonary disease (COPD), and dementia and Alzheimer's Disease may contribute to depression. This association may result from physiological changes associated with these conditions, such as changes in various neurotransmitters, hormones and the immune system, or from associated disability and poor quality of life. In addition, some medications used to treat physical illnesses tend to cause depression. People who cope with more than one medical condition may be at particular risk for depression. Effective treatment of chronic physical illness includes the assessment, early detection and treatment of depression.

What are the Symptoms of Depression?

Each person is different and will have unique symptoms, but here are some of the more common symptoms of depression:

  • feelings of sadness and loss
  • feelings of guilt and worthlessness
  • feelings of extreme impatience, irritability, or a short temper
  • loss of interest or pleasure in usually-enjoyed activities
  • changes in weight or appetite
  • changes in sleeping patterns like insomnia
  • reduced ability to think clearly or make decisions
  • difficulties in concentrating or with short term memory loss
  • constantly feeling tired
  • noticeable lack of motivation
  • anxiety and restlessness, sometimes leading to panic attacks
  • muscle and joint pain
  • constipation or other intestinal problems
  • frequent headaches
  • lack of interest in sex
  • recurring thoughts of suicide or self-harm
  • withdrawal from friends and family.

If you or someone you know has had at least five symptoms for more than two or three weeks, contact your doctor, or a registered mental health professional to discuss the symptoms.

If you or someone you know is having recurring thoughts of suicide it's very important that they get medical help right away.

Facts and Figures

One year prevalence of depression:

  • major depression - 4.8%
  • bipolar disorder - 1.0%

Source: "The Human Face of Mental Health and Mental Illness In Canada 2006"

Additional Resources


  1. Public Health Agency of Canada. The Human Face of Mental Health and Mental Illness In Canada 2006. Public Health Agency of Canada; 2006: P 59.
  2. Canadian Psychiatric Association. Canadian clinical practice guidelines for the treatment of depressive disorders. Can J Psychiatry. 2001;46:Supp1.
  3. Spaner D, Bland RC, Newman SC. Major depressive disorder. Acta Psychiatr Scand. 1994;Suppl 376:7-15.
  4. Fogarty F et al. Op cit. 11 Fogarty F, Russell JM, Newman SC, Bland RC. Mania. Acta Psychiatr Scand. 1994;Suppl376:16-23.
  5. De Marco RR. The epidemiology of major depression: implications of occurrence, recurrence, and stress in a Canadian community sample. Can J Psychiatry. 2000;45:67-74.
  6. Evans D, Charney DS, Lewis L, Golden RN, Gorman JM, Krishnan KRR, et al. Mood disorders in the medically ill: scientific review and recommendations. Biol Psychiatry. 2005;58:175-89.