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What is depression?

We all feel sad, low, or irritable sometimes. It is a natural human emotion to feel down when life gets hard. These feelings usually pass over time. However, some people experience these feelings intensely for weeks, months, or even years. Often the reason is not apparent. This is called depression.

Depression is a serious mood disorder that affects how you feel, think, and manage daily activities. Depression is not a choice, a character flaw, or a moral failing. Rather, depression is an illness in the same way that cancer, diabetes, and heart disease are illnesses.

You are not alone. The World Health Organization (WHO) characterizes depression as the most disabling disorder in the world, affecting roughly 1 in 5 women and 1 in 10 men at some point in their lifetime. Depression occurs at similar rates around the world. In the U.S., it is estimated that 22 out of 100 (22%) of women and 14 out of 100 (14%) of men between the ages of 18-64 will experience depression at some point in their lifetime.

Depression does not discriminate. Men and women of every age, race, ethnicity, educational level, and social and economic background suffer from depression. The problems that result from depression often get even worse because most people with depression are never diagnosed, let alone treated.

There are ways you can feel better. When depression is identified and treated, its symptoms are manageable and there are many effective strategies for living with the disease. Depression and bipolar disorder are both treated most effectively in their earliest stages when symptoms are less severe.

Depressive illnesses take many forms, and their symptoms combine differently in each individual. Some people with depression experience only a few symptoms, while others experience many. Severity of symptoms also varies by individual and changes over time. If you’ve had a change in your normal mood and have been experiencing at least 5 of the signs and symptoms below for more than 2 weeks most of the day, nearly every day, you may be depressed.


  • Sadness
  • Hopelessness
  • Guilt
  • Moodiness
  • Restlessness, irritability
  • Loss of interest in friends, family, and favorite activities, including sex


  • Trouble concentrating
  • Trouble making decisions
  • Trouble remembering
  • Thoughts of harming yourself
  • “I’m a failure.”
  • “I’m worthless.”
  • “I'm a burden.”
  • Delusions and/or hallucinations can also occur in cases of severe depression


  • Withdrawing from people
  • Substance abuse
  • Missing work, school or other commitments
  • Attempts to harm yourself

Physical problems:

  • Tiredness or lack of energy
  • Unexplained aches and pains
  • Headaches
  • Changes in appetite
  • Digestive problems
  • Weight loss
  • Weight gain
  • Changes in sleep – sleeping too little or too much
  • Sexual problems

Of course, all of us can expect to experience one or more of these symptoms on occasion. An occurrence of any one of these symptoms on its own does not constitute depression. When doctors suspect depression, they commonly look for groups of these symptoms occurring regularly and interfering with a person’s daily life.

Depression and other mental illnesses are disorders of brain function. The causes of depression are not fully understood, but current research suggests that depression, bipolar disorder, and related illnesses result from a complex combination of a person's genes and their environment.

Personal Factors

  • Brain chemistry- Changes in how certain chemicals function in the brain may lead to depression.
  • Personality– People with low self-esteem, who are self-critical or overly sensitive to criticism, and/or perfectionists are more likely to develop depression.
  • Serious medical illness– The worry and stress of dealing with a serious illness can lead to depression.
  • Drug and alcohol use– Drug and alcohol use can lead to depression, and people with depression often develop drug and alcohol problems. Prescription drug use can also lead to symptoms of depression.
  • Family history– People with a history of depression in their close family members may be at an increased genetic risk for depression.

Life Circumstances 

Long-term difficulties- Ongoing stress caused by issues such as a stressful relationship or work stress can lead to depression over time.

  • Life events- Stressful times or events such as getting divorced or losing your job, or even positive changes like getting married, may trigger depression in people who are already at risk.
  • Trauma or grief- Physical or emotional abuse or grief after the death of a loved one can trigger depression in people who are already at risk. Stressful childhood experiences such as abuse, neglect, or witnessing domestic violence are common and have a strong influence on many health and social problems, including depression, anxiety, and risk of suicide.

There are several different types of depression that range in severity.

Major Depressive Disorder (MDD) (clinical depression)
MDD is a mood disorder characterized by low mood and/or loss of interest and pleasure in activities. Depression is classified as “major” if someone experiences at least 5 symptoms of depression that interfere with daily life and functioning over a period of 2 weeks.

Persistent Depressive Disorder (PDD)

PDD is a milder form of depression that lasts for at least 2 years. The symptoms of dysthymia are similar to those of major depression but are less severe and longer-lasting.

Melancholic depression

Melancholic depression is a severe form of depression that is characterized by a complete loss of pleasure in all or almost everything, despair, and emptiness. Someone with this form of depression may experience extreme slowness of movement or irregular movement. The depression is regularly worse in the morning and is accompanied by lack of appetite and weight loss.

Perinatal depression
Perinatal depression is major depression that occurs during pregnancy or within a year after delivery (postpartum depression). Women frequently experience mild mood changes during or after pregnancy, but if these symptoms become severe, they may require treatment. Symptoms include extreme sadness, anxiety, exhaustion, and difficulty bonding with the baby, making it difficult for women to complete daily care activities for themselves and/or for their babies.

Psychotic depression 
Psychotic depression occurs when a person with a depressive disorder loses touch with reality and experiences some kind of psychosis, such as having disturbing false beliefs that are not shared by others (delusions) or seeing or hearing upsetting things that are not really there (hallucinations).

Seasonal affective disorder (SAD)

SAD is depression that takes place during the fall and winter months, when there is less natural sunlight. SAD generally lifts during spring and summer and returns every year. It is characterized by social withdrawal, increased sleep, weight gain, and hopelessness. Light therapy is often prescribed as a treatment for SAD.

Treatment-resistant depression (TRD) 
TRD is a term used to describe cases of depression that do not respond well to treatment. Treatment may not help much, or symptoms may improve but keep coming back. TRD may require various treatments to identify what helps. Doctors are now recognizing that a significant percentage of people with depression have TRD. As awareness of TRD has increased, so have the new approaches to address this condition.

Situational Depression
Situational depression is a short-term form of depression that can occur following stressful life events, including divorce, retirement, loss of a job and the death of a relative or close friend. 

When diagnosing MDD, doctors must rely on a careful analysis of symptoms over time. Doctors use the following criteria from the American Psychiatric Association’s guidelines to make a formal diagnosis.

Depressed mood or a loss of interest or pleasure in daily activities for more than two weeks.

  • Mood represents a change from the person's norm
  • Impaired function: social, occupational, educational
  • At least 5 of these 9 symptoms are present nearly every day:
    • Depressed mood or irritable most of the day, nearly every day
    • Decreased interest or pleasure in most activities, most of each day
    • Significant weight change or change in appetite
    • Change in sleep
    • Change in activity level
    • Fatigue or loss of energy
    • Guilt/worthlessness: Feelings of worthlessness or excessive or inappropriate guilt
    • Concentration: Difficulty concentrating or thinking
    • Suicidality: Thoughts of death or suicide, or has suicide plan

Take the PHQ-9 to help you begin to explore whether the feelings, thoughts or behaviors you may be experiencing could be depression. Use this tool as a guide only. It should not be used in place of a doctor’s evaluation. If you believe you may be suffering from symptoms of depression, talk to your doctor.

Anda, R. F. (2009). The health and social impact of growing up with adverse childhood experiences.

Kessler, R. C., Petukhova, M., Sampson, N. A., Zaslavsky, A. M., & Wittchen, H. U. (2012). Twelve?month and lifetime prevalence and lifetime morbid risk of anxiety and mood disorders in the United States. International journal of methods in psychiatric research, 21(3), 169-184.

Lam, R. W., McIntosh, D., Wang, J., Enns, M. W., Kolivakis, T., Michalak, E. E., ... & Milev, R. V. (2016). Canadian Network for Mood and Anxiety Treatments (CANMAT) 2016 clinical guidelines for the management of adults with major depressive disorder: section 1. disease burden and principles of care. The Canadian Journal of Psychiatry, 61(9), 510-523.

National Institute of Mental Health. (2016). Depression. Retrieved on November 29, 2017 from