Depression, or major depressive disorder, is a mental health condition marked by an overwhelming feeling of sadness, isolation and despair that affects how a person thinks, feels and functions. The condition may significantly interfere with a person's daily life and may prompt thoughts of suicide. Depression isn't the same as sadness, loneliness or grief caused by a challenging life experience, such as the death of a loved one.
In 2015, an estimated 16.1 million U.S. adults (aged 18 or older), or 6.7 percent of the adult population, had at least one major depressive episode, or experienced depressive symptoms, in the past year, making this condition one of the most common mental disorders in the United States, according to the National Institute of Mental Health (NIMH).
Depression can affect people of all ages, races and socioeconomic classes, and can strike at any time. The condition is found in twice as many women as men, according to the NIMH.
In a recently published report from the Centers for Disease Control and Prevention, researchers found that women between 40 and 59 have the highest rate of depression (12.3 percent) of any group based on age and gender in the United States.
People with depression may experience a variety of symptoms, but most commonly, "a deep feeling of sadness or a marked loss of interest or pleasure in daily activities," according to the American Psychiatric Association. Other symptoms of depression may include:
- Irritability, agitation or restlessness
- Lower sex drive
- Inability to focus, concentrate or make decisions
- Insomnia or sleeping too much
- Change in appetite and/or weight, eating too much or too little
- Tiredness and lack of energy
- Unexplainable crying spells
- Unexplainable physical symptoms such as headaches or body aches
- Feeling hopeless or worthless
- Withdrawal from social situations and normal activities
- Thoughts of death or suicide
The causes of depression are not fully understood, but scientists think that an imbalance in the brain's signaling chemicals may be responsible for the condition in many patients. However, there are several theories about what this imbalance actually is and which signaling chemicals are involved. Moreover, a variety of distressing life situations are also associated, including early childhood trauma, a job loss, the death of a loved one, financial troubles or a divorce.
Most likely, depression is caused by a combination of genetic, biological, environmental, and psychological factors, according to the NIMH.
Certain medical conditions may also trigger depression, including an underactive thyroid gland, cancer, heart disease, prolonged pain and other significant illnesses. Hormonally induced depression can arise after childbirth or at menopause as well.
Additionally, some sedatives, such as sleeping pills, and high blood pressure medications are linked to depression, according to the NIH.
To diagnose a person with depression disorder, doctors may ask patients about their family health history, mood and behavior patterns (such as eating and sleeping), and thoughts of suicide. They may also ask patients to report their depression symptoms on a printed questionnaire.
In the Diagnostic and Statistical Manual of Mental Disorders (DSM), which is a mental health guidebook for doctors published by the American Psychiatric Association, to diagnose a person with major depressive disorder, the person must show five or more of the symptoms (listed above) for at least two weeks. The person must also exhibit a depressed mood, or loss of interest or pleasure.
It must also be ruled out that the symptoms are not caused by another medical condition, such as a thyroid problem, or due to the direct effects of a drug or medication. So doctors may do a blood test, or test the thyroid to make sure it's functioning properly, according to the Mayo Clinic.
And lastly, doctors look at whether "the symptoms cause clinically significant distress or impairment in social, occupational or other important areas of functioning," according to the DSM.
Surveys have shown that up to half of Americans with depression don't get medical help for their condition. Left untreated, major depression can set off a chain of social, emotional and health consequences that add to patients' overall stress. According to the Mayo Clinic, these include alcohol or drug abuse, anxiety, social isolation and relationship conflicts, work or school difficulties, or suicide.
Depression treatment may involve psychotherapy therapy, medications, or a combination of the two.
Medication: Prescription drugs, called antidepressants, help alter mood by affecting naturally occurring brain chemicals. There are several categories of antidepressants, but doctors often start with a class of drugs called selective serotonin reuptake inhibitors (SSRIs), and may try other medications if the patient's condition didn't improve.
SSRIs target the brain's serotonin, a signaling chemical (neurotransmitter) that studies have found to be involved in depression. This class of medication includes fluoxetine (commonly known as Prozac), sertraline (Zoloft), paroxetine (Paxil), escitalopram (Lexapro) and citalopram (Celexa). Side effects, which are usually temporary, include changes in sexual desire, digestive problems, headache, insomnia and nervousness.
Other classes of antidepressants include serotonin and norepinephrine reuptake inhibitors (SNRIs), Norepinephrine and dopamine reuptake inhibitors (NDRIs), Tricyclic antidepressants, and Monoamine oxidase inhibitors (MAOIs).
Medications take time — usually 2 to 4 weeks — to work, and often symptoms such as appetite, concentration problems and sleep improve before people may notice mood changes, according to the National Institute of Mental Health.
Psychotherapy: Also known as talk therapy or counseling, this treatment has been shown to help some patients with depression. Several studies have suggested that combining psychotherapy and medication together works best for treating people with severe depression. Different types of psychotherapy include cognitive-behavioral therapy, which helps a person change negative thought patterns and replace them with healthier ones, as well as interpersonal therapy, which is designed to help someone understand and work through difficult relationships, according to the National Institute of Mental Health. Another form of psychotherapy is problem-solving therapy, which involves coming up with realistic solutions to cope with stressful situations.
Less common treatments: For patients with severe depression who have not responded to any medication or psychotherapy, doctors may consider transcranial magnetic stimulation (TMS), according to the Mayo Clinic. TMS involves receiving brief magnetic pulses on the scalp to stimulate nerve cells in the brain that are thought to be involved in mood regulation and depression.
Additional reporting by Cari Nierenberg, Live Science contributor