Depression disorders are among the most common and destructive mental health issues in the world. Major depressive disorder, the most common type of depression, affects an estimated 6.7 percent of American adults, and is the leading cause of disability for workers aged 15 to 44. Depression can vary in scope and intensity, and as a class of mood disorder, depression disorders are characterized by low mood and feelings of low self-worth.

Other types of depression include persistent depressive disorder, premenstrual dysphoric disorder, disruptive mood dysregulation disorder, substance-induced disorder, seasonal affective disorder, and other specified or unspecified depressive disorders. A distinction may also be made for depressive disorders caused by another medical disorder (such as chronic or terminal pain from cancer).

The defining characteristics of depressive disorders is the severely low mood, which separates itself from healthy or normal sadness by intensity and duration. Depression can also include physical and cognitive symptoms, particularly signs of chronic fatigue, significant changes in weight (loss or gain), difficulties with problem solving and decision making, and a diminished capacity to concentrate or think about one thing.

The sluggishness and loss of interest caused by depression is sometimes mistaken for or described as laziness, which can further reinforce the self-deprecating thoughts many depressed people struggle with, leading into a developing cycle of negative thoughts and behaviors.

Genetics play a part in the development of depression disorders, but so does environment. Certain types of stress can lead to the development of depressive symptoms, including loss of a loved one, overwhelming work or school stress, or a chronic state of stress.

While we aren’t exactly sure yet how depression occurs in the brain, we do know that there are many systems that regulate and reinforce mood and behavior, and different cases of depression may have different underlying factors.

For example, in some cases, depression may be largely impacted by the part of the brain that regulates emotions and memory and reinforces behavior or triggers inhibitions through the release of certain chemicals, like dopamine and GABA.

In other instances, people may be predisposed towards depressive thoughts during the winter, as a result of holiday stressors, low levels of natural sunlight, and the prolonged effects of darkness.

Some women experience severe depression and suicidal ideation in the luteal phase of their menstrual cycle, before the period starts.

Substance use disorders (addiction) can also play a role in the development of depression, and vice versa. Prolonged drug use can have a substantial effect on the brain, making people more likely to experience severe negative shifts in mood, irritability, and thoughts of self-harm.

In other cases, it’s the factors surrounding their addiction (such as homelessness, a traumatic experience, or chronic stress) that contributed the most to their depression.

Other medical conditions can lead to depression as a result of pain, or because of mood changes triggered by endocrine disorders (like hypothyroidism).

These different types of depression require different forms of therapy and medication. Aside from psychotherapy, other forms of therapy can help people with depression find ways to better cope with their thoughts and learn to isolate them, through cognitive behavioral therapy (CBT), and through therapies that help introduce people to hobbies and activities that promote mental wellbeing, such as art therapy and equine therapy. For some people, inpatient or outpatient treatment is necessary to safely treat their depression, and ensure that they’re safe, especially if they have frequent suicidal thoughts or a history of self-harm.