Depression is a mood disorder characterised by an excessive absence of enjoyment, a prolonged duration of sadness, or an aversion to activity.

While most people naturally experience acute periods of low moods, including feelings of sadness and grief, for clinical depression symptoms must persist for at least two weeks. While death, loss, or illness can bring on bouts, depression can often lack a clear cause or seem unreasonable in intensity of emotion.

The condition is considered to be a leading cause of disability worldwide, with roughly one in 10 individuals experiencing at least one period of clinical depression at some point in their lives.

In addition to reducing the quality of life among those experiencing the condition, it adds an economic burden estimated to more than US$210 billion per year and dramatically increases the risk of suicide, making it a serious illness that demands attention.

How do you know if you have depression?

The symptoms of depression can be diverse and relative to individual experiences. Most are characterised internally by a sense of what is referred to as anhedonia - dulled or a complete absence of joyful or excited emotions.

In more extreme cases, the mood extends to a sense of hopelessness, grief, or even guilt. This can impact on taking initiative in activities, including work. It can also impact on appetite, sleep, and concentration, and in some cases be accompanied by thoughts of self-harm and suicide.

In many cases physiological symptoms such as headaches or digestive problems can result. Having depression could also put people at risk of developing a number of other seemingly unrelated illnesses, such as heart disease or infections.

When symptoms such as these persist for two weeks or more, people are encouraged to seek help from their doctor or talk to a councillor.

What causes depression?

It's not unusual for people to discuss the cause of depression as a form of 'imbalance' in the brain's neurochemistry. While mood disorders like depression are based largely on physical differences in the nervous system, the complete answer on what causes depression is likely to be rather complicated.

Differences in the size and activity of certain regions of the brain, such as the hippocampus, could play a role in some individuals, for example. But this is just one small component, with a variety of networks throughout the brain implicated by diverse studies.

In many people, genes are also likely to contribute to the risk of developing depression, however the impact of the environment - whether work, drugs and medication, or lifestyle - remains a major determining factor in how depression manifests.

Are there different kinds of depression?

Chronic clinical forms of depression can be categorised based on associated symptoms and concurrent life events. Today, clinical depression is primarily diagnosed through behavioural assessments, though a precise diagnosis can be made harder with the prevalence of comorbidities such as bipolar disorder.

Dysthymia (also called persistent depressive disorder) is what most people think of when they think of depression as an illness. While the intensity of symptoms vary over time, this form of the illness is characterised by a diagnosis that lasts for two years or more. Major depressive disorder can be diagnosed where signs of anhedonia and motor symptoms such as lethargy persist.

Psychotic forms of depression are linked with experiences of delusive beliefs or hallucination. There can be dominant themes to the depressive episodes, associated with feelings of guilt or signs of other illnesses.

Postpartum depression is a significant period of low mood, exhaustion, and sadness that is linked with pregnancy and delivery, to the extent that new parents find it hard to care for their newborn or enjoy their company.

Similarly, seasonal affective disorder is also defined by the timing of depressive symptoms, typically occurring during winter months when there is low natural light and reduced outdoor activity. Whether this form of depression is a true reflection of the environment is still a debated topic.

How is depression treated?

Treatments for depression are traditionally based on either pharmaceuticals or psychological interventions, such as cognitive behavioral therapy. Lifestyle changes, such as exercise, bright light exposure during waking hours, or socialising, can also make a difference in many cases.

Often a combination is used, depending on the type or severity of the condition and the patient's responsiveness and willingness.

Future treatments could include forms of magnetic stimulation to the brain's neural networks, novel medications, or known forms of psychedelics and other drugs, like ketamine or psilocybin, used in controlled amounts alongside traditional therapies.

If this article has raised concerns or you need to talk to someone, here's a list where you may be able to find a crisis hotline in your country.

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