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A young woman sitting in bed with her head in her lap, she is in pain or depressed.
May 3, 2019

How is Depression Caused?

Depression is one of the most common mental illnesses in the United States. Statistics from the National Institute on Mental Health (NIMH) show that an estimated 17.3 million adults in the U.S. had at least one major depressive episode in 2017, while an estimated 11 million adults in America had at least one major depressive episode with severe impairment. In addition, about 3.2 million adolescents had at least one major depressive episode in 2017. Clearly, depression is a mental health concern. But what is depression and how is depression caused?


As defined by the American Psychiatric Association (APA), depression (major depressive disorder) is “a common and serious medical illness that negatively affects how you feel, the way you think and how you act.” Depression causes feelings of sadness losing interest in things once enjoyed, can lead to many emotional and physical problems and decrease the ability to function at work, home and elsewhere. Depression is also treatable and, indeed, is one of the most treatable of all the mental disorders. According to the APA, between 80-90 percent of those with depression “eventually respond well to treatment,” while almost all get some relief from depression symptoms.

Differences Between Depression and Sadness or Grief

It is important to note that depression is different from sadness and grief or bereavement. You might feel very sad or experience grief if you lose your job, a loved one dies, or a relationship ends. You might say you’re depressed, but you don’t have depression. In fact, in such situations, it’s normal to feel sad.

Grief occurs in stages, with difficult or painful feelings in waves, sometimes mixed with good memories of the person who died. Major depression, however, is characterized by decreased mood, pleasure or interest for a period of two weeks. Someone who is grieving usually maintains their self-esteem, while those suffering from depression commonly feel worthless and self-loathing.

On the other hand, grief that co-occurs with clinical depression can be more severe and longer lasting than without the presence of depression.


The National Institute of Mental Health lists some of the forms of depression that are either slightly different or develop under unique circumstances. These include:

  • Dysthymia (persistent depressive disorder) – This is a depressed mood that lasts at least 2 years.
  • Postpartum depression – Much more serious than so-called “baby blues” that many women experience after giving birth and that are typically gone a couple weeks after delivery, postpartum depression is characterized by extreme sadness, exhaustion and anxiety. Suffering from postpartum depression can make it difficult for new mothers to properly care for their babies and even themselves.
  • Psychotic depression – This occurs when an individual has severe depression along with a form of psychosis – such as delusions or hallucinations. Their psychotic symptoms are thematically depressive, including delusions involving illness, guilt, or poverty.
  • Seasonal affective disorder – This form of depression comes on during the time of less natural sunlight, typically the winter. It generally lifts in the spring/summer. Weight gain, sleeping more, and social withdrawal typically accompany winter depression, and seasonal affective disorder returns every year, in general.


Symptoms of depression can vary from mild to moderate to severe. To be diagnosable as depression, the symptoms must last at least two weeks. Symptoms can include:

  • Persistent sadness, anxiousness, feeling empty
  • Aches, pains, digestive problems – without clear physical cause, and/or that do not get better with treatment
  • Appetite changes – resulting in weight gain/loss unrelated to dieting
  • Energy loss, fatigue
  • Feelings of worthlessness, helplessness, or guilt
  • Impaired thinking, remembering, concentration or decision-making
  • Increase in “purposeless” physical activity, such as pacing, hand-wringing), visibly (observed by others) slowed speech and movements
  • Irritability
  • Lack of interest/pleasure in once enjoyable activities
  • Restlessness, inability to sit still
  • Sleep difficulties – sleeping too much, trouble sleeping
  • Suicidal thoughts, thoughts of death


As with other forms of mental illness, there is no single cause of depression. The APA lists several risk factors that play a role in the development of depression. These include:

  • Genetics – Depression can run in families. If you have parents or a twin that has depression, you’re at higher risk of developing depression. The twin of a sibling with depression has a 70 percent chance of one day developing the mental illness.
  • Biochemistry – Experts say that certain chemicals in the brain and their differences may somehow contribute to developing depression. Poor functioning of the hypothalamus, pituitary gland, and frontal lobe have been implicated in depression development.
  • Environmental – Long-time exposure to certain toxic environmental factors, such as violence, poverty, neglect or abuse may make some individuals more vulnerable to the onset of depression.
  • Personality – Researchers say that those who find themselves overcome by stress, are generally pessimistic, or have low self-esteem are more likely to have depression.

The National Alliance on Mental Illness (NAMI) adds that early-age trauma can be a factor in developing depression. In addition, about 30 percent of those with drug and alcohol abuse also have depression. Such dual diagnosis requires coordinated treatment, due to the fact that alcohol abuse can worsen depression symptoms. Furthermore, some medical conditions may make a person more susceptible to developing depression, including chronic pain, sleep disturbances, anxiety, medical illnesses, and attention-deficit hyperactivity disorder (ADHD). Some medications are known to cause depression symptoms as well.

Various research findings show evidence that some of the body’s natural body changes associated with aging could increase depression risk. Indeed, as an article in the American Psychological Association points out, recent studies suggest that decreased folate concentrations in the blood and nervous system may be a contributing factor to depression, mental impairment and dementia. There is also a suspicion on the part of researchers of a link between late-life depression onset and Alzheimer’s disease.

The National Institute on Drug Abuse (NIDA) notes that both mental illnesses and substance use disorders (SUDs) are caused by “overlapping factors such as genetic and epigenetic vulnerabilities, issues with similar areas of the brain, and environmental influences such as early exposure to stress or trauma.”


Looking at the symptoms, you may believe that you have depression. The only way to know for sure is to make an appointment with your doctor (either your primary care physician or a medical professional who specializes treating mental health conditions, such as a psychiatrist or psychologist). Talk with the doctor about what you are experiencing. Certain medical conditions can mimic depression symptoms and the doctor can rule them out by conducting certain lab tests, doing a physical examination, and a thorough interview.

If the test results do not indicate a medical condition causing your depression, the doctor will then progress to a psychological evaluation and may refer you to a mental health professional. Discussions will include any family history of depression or other mental disorder, personal and family alcohol or drug use. Give a complete history of your symptoms, and be sure to mention what your symptoms are specifically, when they began, how severe they are, have they occurred before, and if they were treated, how were they treated.


If you are diagnosed with depression, be aware that the illness is highly treatable with medications, psychotherapy, behavioral interventions, good self-care, support groups and coping strategies. The first step, after a thorough diagnostic evaluation, is the development of a personalized plan to address your specific needs.

Medication — Your treatment provider may prescribe antidepressants to help modify your brain’s chemistry. These are not addictive medications and generally do not produce a stimulating effect. There should be some relief from symptoms within the first 1-2 weeks of use, although greater improvements may take a few months. Psychiatrists recommend continuing the medication regimen for 6 months or longer after symptom improvement. Long-term medication maintenance treatment may be recommended for high risk individuals.

Psychotherapy – Mild depression is sometimes treated alone with psychotherapy. For those with moderate to severe depression, psychotherapy is often combined with antidepressant medication. In addition to individual (one-on-one) therapy, psychotherapy may include group therapy, family therapy, or couples therapy. Other evidence-based treatments may include cognitive-behavioral therapy (CBT), which helps the individual to recognize and reframe distorted thinking and learn to present focus and problem solving. The duration of psychotherapy treatment may last many months, although significant improvement is often seen in 10-15 weeks.

Electro-convulsive therapy may be recommended, as it has proven effective in treating depression. Also, in 2008, the Food and Drug Administration (FDA) approved transcranial magnetic stimulation (TMS) to treat those with major depressive disorder (MDD) for whom standard drug therapy has been ineffective.

Self-Care – Getting sufficient sleep, regular exercise, healthy eating and avoiding alcohol (which is a depressant) help many people with depression reduce the symptoms they experience.

Support Groups – Talking with others going through depression or after treatment for it is also recommended. This encourages you and makes you realize you’re not alone. You can get through this and learn effective coping strategies as you continue to make headway in your recovery from depression.

The National Institute of Mental Health has a number of publications available on the subject of depression that you may find helpful.

For more about depression, other mental health conditions, substance abuse, addiction and recovery, check out these articles:

How Family Involvement Improves Recovery from a Dual Diagnosis

Common Co-Occurring Disorders Associated With Addiction

The Connection Between Alcohol and Depression