Depression, or a depressed mood, can have many causes. For some people, depression is a reaction to life stresses, while for others it might come and go with the turning of the months or seasons. The Centers for Disease Control and Prevention (CDC) report that in one survey among 235,067 adults, about 9 percent of people currently met criteria for some form of depression.
Major depressive disorder
Major depressive disorder, or major depression, is one of the most commonly occurring mental illnesses in the United States. According to the Substance Abuse and Mental Health Services Administration (SAMHSA), about 7 percent of American adults have had at least one episode of major depression in the last year. Research in the Archives of General Psychiatry found that about 13 percent of people experienced major depression within their lifetimes.
To meet criteria for an episode of major depression, you must experience (or have someone observe) at least five of the following symptoms in a two-week period, with at least one of those symptoms being either depressed mood or an inability to feel interest or pleasure in normally enjoyable activities:
- Depressed mood that lasts for the majority of the day most days of the week
- Loss of ability to enjoy or care about activities that were previously interesting, which occurs nearly every day
- Significant loss of appetite, or loss of weight (when not dieting)
- Difficulty sleeping, or sleeping too much, nearly every day
- Being overly restless
- Regular loss of energy, or fatigue
- Inappropriate or excessive feelings of guilt or worthlessness
- Difficulty thinking straight or concentrating, or indecisiveness
- Thoughts of death and suicide, with or without a plan for committing suicide
If these symptoms are causing a significant loss of functioning at work or school, or problems among family or friends, then major depressive disorder may be the cause.
Major depression usually responds to psychotherapy like cognitive behavioral therapy and to antidepressants like SSRIs. For people with severe, chronic depression that does not respond well to talk therapy and medication, other options include electroconvulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS). These treatments use electrical signals to help reset and retrain the brain to have healthy wave patterns.
Persistent depressive disorder (chronic MDD, dysthymia)
The most recent version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) groups together chronic major depressive disorder with dysthymia, a less severe form of depression, under the heading of persistent depressive disorder. This form of depression is characterized by a depressed mood that has been prevalent for at least two years. A person with persistent depressive disorder may go through episodes of major depression alternating with periods of milder depressive symptoms, so long as symptoms last at least two years.
Specifiers of depression
In addition to a diagnosis of major depression, diagnosticians may also include a specifier, describing a subtype of depression.
- Inability to feel pleasure or happiness
- Feelings of numbness, hollowness, or emptiness
- Feelings of mental or physical slowness
- Sleeping more than usual
- Difficulty getting going in the morning
- Difficulty accomplishing simple tasks, like showering or getting the mail
- Difficult paying attention and concentrating
- Shifts in appetite, usually resulting in weight gain or weight loss
- Physical signs of agitation, such as hand-wringing or pacing
- Not feeling better, even temporarily, when something positive happens
- Feeling heavy or leaden, especially in the arms and legs
- Increased sleep
- Increased appetite and weight gain
- Oversensitivity to being rejected by others
According to a review in Psychiatry (Edgmont), atypical depression is the most common subtype of depression, and tends to have an earlier age of onset than other subtypes.
- Long periods of not moving
- Holding bizarre positions
- Resisting being moved
- Inability to speak at times
- Repeating behaviors over and over
- Mimicking the behaviors of others
Seasonal affective disorder
This may be considered a specifier of major depression, or it may be considered its own disorder. For people with seasonal affective disorder (SAD), moods vary based on the season, particularly according to the amount of daylight hours the person experiences. Natural daylight (or lamps that mimic it) is necessary for the brain to tune its internal clock, which in turn regulates hundreds of functions in the body. In SAD, this process seems to have gone awry. According to the National Alliance on Mental Illness (NAMI), SAD is more commonly found in northern latitudes like Canada and Alaska than farther south, like in California and Florida.
People with SAD will find that their symptoms begin to appear in the late summer, fall, or early winter, as the daylight hours grow short. For some people, the lost daylight of daylight saving time ending can be the trigger. Depressive symptoms in winter can include:
- Fatigue during the day
- Craving carbohydrates
- Weight gain
- Loss of sexual interest
- Decreased social activity
- Loss of interest in hobbies and enjoyable activities
- Feelings of hopelessness or suicidal thoughts
As the daylight hours begin to increase in length in March and April, these symptoms will gradually wane, with people feeling “back to normal” around early May. Some people with SAD also find that their depression symptoms are worse on days with reduced light, like overcast days, or when they have insufficient interior lighting.
It’s not uncommon for people with SAD to experience a different set of depressive symptoms during the summertime, which might bear a closer resemblance to symptoms of bipolar disorder (manic depression):
- • insomnia
- • loss of appetite
- • weight loss
- • anxiety or agitation
In addition to using psychotherapy and antidepressant medication (which may only be necessary in winter months), SAD can also be treated with light therapy. This uses bulbs that emit similar wavelengths of visible light as the sun, stimulating special cells in the eyes that conduct the signal to the brain’s clock. People with bipolar disorder with a seasonal component should be careful using light therapy, as it can potentially trigger a manic episode.
Bipolar disorder (maniac depression)
Major depression is also called unipolar depression. Bipolar depression, also called bipolar disorder or manic depression, occurs when a person cycles between two extremes. One extreme bears a strong resemblance to major depression, with largely the same symptoms. The other extreme, called mania, is characterized by:
- Racing thoughts
- Rapid speech
- Inflated self-esteem
- Increased physical activity
- Increased focus on achieving goals or performance
- Aggression, agitation, or irritation
- Lack of inhibition
- Risky behavior or impulsive, unwise decision-making
- Decreased need for sleep
- Poor performance at or absences from work or school
Cycling between states may occur slowly over weeks, or it may happen multiple times a day. The distribution of mania and depression will vary depending on what type of bipolar disorder the person has.
- Bipolar I disorder features a mixture of mania and depression.
- Bipolar II disorder largely features severe depression but also periods of hypomania (low-grade mania).
- Cyclothymic disorder is low-grade cycling between hypomanic and depressive symptoms without ever fully meeting the criteria for hypomania or depression.
Bipolar disorder has affected 2.6 percent of American adults in the past year, according to NIMH.
Although antidepressants may be useful for treating the depressive stages of bipolar disorder, they may trigger or aggravate mania. Bipolar disorder may respond better to mood stabilizers, many of which also have indications for depression and anxiety.
- Major life changes, like marriage or the birth of a child
- Stressors, like a big deadline at work or school
- Losses, like the death of a loved one, a divorce, or loss of a job
Situational depression is more responsive to lifestyle changes, such as eating right, sleeping regularly, reaching out to loved ones for support, focusing on hobbies, getting lots of exercise, and getting enough sunlight. Some people may also find that they benefit from support groups, which offer addition social resources, or psychotherapy. Antidepressants may be appropriate for short amounts of time, such as in the months following the stressful event.
Substance- or medication-induced depressive disorder
Often, the effects of a drug or withdrawal from the drug can cause symptoms of depression. These symptoms usually wear off once the drug has cleared the person’s system and withdrawal has been completed. Such drugs may include:
- Sedative or hypnotic drugs, like alcohol, opiates, and benzodiazepines, or withdrawal from them
- Cocaine, methamphetamine, and other stimulants, which can cause a depressive “crash” after their use
- Hallucinogens, which can cause a “bad trip” that can trigger depression lasting for weeks or months
- Steroids, such as those used to treat autoimmune problems like allergies
- Hormonal birth control
- Cardiovascular medications
- Smoking cessation medications
Depressive disorder due to a medical condition
Some medical conditions can affect hormones or neurotransmitters in the brain, interfering with the brain’s natural pathways for mental health, and triggering depression. These can include:
- Brain injury, including from stroke
- Parkinson’s disease
- Huntington’s disease
- Cushing’s disease
- Polycystic ovarian syndrome (PCOS)
- Multiple sclerosis
For such people, treating the underlying medical condition usually makes the depressive symptoms go away.
Other psychiatric conditions that can include depression as a symptom
Some other mental illnesses have depression as a possible symptom, according to SAMHSA. These include:
- Post-traumatic stress disorder (PTSD)
- Anxiety disorders, such as:
- Panic disorder
- Social phobia
- Generalized anxiety disorder
- Schizoaffective disorder and schizophrenia
- Personality disorders