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.

Most likely, depression is caused by a combination of genetic, biological, environmental, and psychological factors, according to the NIMH.


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.

Treatment
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.