Depression is a mental state characterized by a pessimistic sense of inadequacy and a despondent lack of activity, and is often characterized by feelings of sadness, helplessness and hopelessness. It is a mental illness, and because of this, many factors influence its development, from personal experiences and emotions to hormonal changes and hereditary genes. Depression comes in many different forms and degrees, and is often accompanied by other disorders or medical conditions. Without proper care and attention, people with depression can sink into isolation, darkness, and some even resort to suicide to end their struggle.
According to a recent study done by the World Health Organization and World Bank, the number one cause of disability in the U.S. is depression. In fact, in any given year, around 18.8 million American adults (approximately 9.5% of the adult population) struggle with a depressive disorder. Depression is a serious, diagnosable medical condition that requires proper treatment. It's a worldwide disability that affects all people, regardless of gender, age, economic or social status. 
- 1 Symptoms
- 2 Causes and Risk Factors
- 3 Treatment
- 4 Reactions
- 5 Forms and Related Disorders
- 6 References
- 7 External Links
- 8 Other mental illnesses
Common symptoms of depression include:
- Continual feelings of sadness, "emptiness", or anxiety
- Hopeless or pessimistic outlook
- Restless or irritable emotions
- Feeling guilty, helpless, or insignificant
- Persistent fatigue or low energy
- Problems with concentration, decision-making, or memory
- Losing interest in former hobbies or favorite activities
- Changes in appetite (either weight gain or loss)
- Waking in the early morning hours, insomnia (chronic sleeplessness), or sleeping in excess
- Aches and pains (cramps, digestive difficulties, headaches, etc.) that fail to response to medical treatment
- Contemplation of and/or attempts at suicide 
Causes and Risk Factors
Unlike some medical conditions, depression cannot be traced to a single cause. Research indicates that some genes can increase a person's risk for clinical depression, running in families for generations. It is believed that interaction among multiple genes can lead to depression, but researchers are unable to pinpoint a specific "depression" gene. 
More particularly, the nerve cells in the brain responsible for moods and emotions connect with one another via chemical messengers called neurotransmitters. The body's production and decomposition of these neurotransmitters, as well as various hormones, is believed to result in depression in some individuals.
Early traumatic or abusive experiences in childhood alter the development of emotions and moods, affecting the brain's natural chemistry and response to stress.  Hormonal changes in the body also seem to be a key factor, as women are twice as likely as men to experience depression. Certain health conditions or diseases can increase a person's risk; for example, there is a 65% increase risk for depression after having a heart attack. 
People with a naturally pessimistic outlook and poor self-esteem are also vulnerable to serious depression, and may already suffer from a milder form known as dysthymia. Stressful social changes and events are known to trigger depression, such as a breakup in a relationship or financial troubles, and even joyous occasions like getting married or graduating from school. Preexisting psychological issues like schizophrenia, anxiety, and eating disorders, frequently accompany depression.  Intense feelings of grief associated with the death of a loved one, losing one's job, retirement, or divorce can also lead to depression (depending upon the individual).
Almost 30% of people that struggle with substance abuse also deal with clinical or major depression.  Poor diet resulting in vitamin deficiencies, as well as the use of some prescribed medications, can result in depression. Other risk factors include: a chronic medical condition, personality disorder, continual emotional or mental stress, obesity, and isolation from society. 
In comparing the brains of people with depression and those without it, researchers have discovered that the hippocampus, a small portion of the brain responsible for storing memories, is notably smaller in people with depression. With a smaller hippocampus, depressed people have fewer chemical receptors, particularly those of serotonin and norepinephrine; these two neurotransmitters have a calming effect on the brain and aid in smooth communication between the brain's nerve cells and the body. Other studies indicate that cortisol, a stress hormone, is overproduced in the brains of depression patients, leading some researchers to postulate that it has a toxic effect on the hippocampus. Still other scientists speculate that people born with a smaller hippocampus are more likely to suffer from depression. In any case, depression is more than just a simple persistent mood; it is a diagnosable medical condition that requires treatment and proper medication. 
Antidepressants are medications that balance out the natural neurotransmitter levels in the brain, specifically serotonin, norepinephrine, and dopamine. These medications take three to four weeks to become effective, and a patient should take them as long as instructed by their doctor, even if symptoms improve, in order to avoid a relapse. When a patient stops taking antidepressants, they must be gradually weaned off or withdrawal effects and a potential relapse could ensue. Sometimes doctors also prescribe a stimulant or anxiety medication in conjunction with antidepressants. Side effects vary depending upon the specific medication, but common side effects include headaches, nausea, sexual and bladder problems, and daytime drowsiness. Combining antidepressants with some medications can lead to serious and life-threatening medical conditions.  The main kinds of antidepressants are:
- Selective serotonin reuptake inhibitors (SSRIs)-- The most common type of depression medication and has only mild side effects;  boosts the serotonin levels in the brain by preventing "serotonin reuptake," a process in which the nerves that release the serotonin also absorb it again, keeping it from being used by other nerves. 
- Serotonin and norepinephrine reuptake inhibitors (SNRIs)-- Prevents serotonin and norepinephrine reuptake. 
- Aminoketones-- A weaker type of antidepressant; how it works is not completely known.
- Tetracyclic antidepressants-- Acts upon serotonin and norepinephrine levels; mild side effects.
- Tricyclic antidepressants (TCAs)-- A class of some of the original antidepressant drugs; can have severe reactions in some people, but is useful if newer antidepressants are ineffective.
- Monoamine oxidase inhibitors (MAOIs)-- One of the earliest antidepressants; inhibits the function of an enzyme called monoamine oxidase that breaks down the neurotransmitter hormones; rarely prescribed due to severe reactions with certain foods and other medicines. 
Although depression is primarily caused by chemical factors in the brain, the psychological connection is unmistakable. Psychotherapy consists of the depressed patient speaking with a professional counselor who then aids the person in recognizing and responding to the factors triggering their depression. Three main types of psychotherapy are: cognitive behavioral therapy, interpersonal therapy, and psychodynamic therapy. Cognitive behavioral therapy focuses on isolating and correcting inaccurate perceptions the patient has; gradually they learn to identify true and false assumptions they have about themselves and their environment. Interpersonal therapy works on the depressed person's relationships with their family and friends. This therapy is recommended for those suffering depression from social and relational difficulties, grief, or a life-changing event, as it improves self esteem and communication skills. Psychodynamic therapy assumes that a person's depression is a result of unsettled and mostly unconscious problems (mostly from childhood); talking about these experiences works to bring closure and better coping techniques regarding the involved emotions. Both interpersonal and psychodynamic therapies are administered for about three to four months.  Even though individual therapy is common, group therapy also has many benefits; it increases the social interaction of people struggling with depression and allows them to draw encouragement from one another. Therapy in general focuses on strengthening and building relationships (attempting to prevent future depression), introducing positive responses to life's difficulties, and establishing healthy boundaries to reduce stress. 
If a patient doesn't respond to other forms of depression treatment, electroconvulsive therapy (ECT) is frequently administered. ECT is also resorted to when a depressed patient is suicidal, needs immediate treatment, or has schizophrenia, major depression, bipolar disorder, etc. In ECT the patient takes a muscle relaxant and is then put under general anesthesia. Electrodes are placed on the patient's head and, using a carefully controlled electric current, stimulate a brief brain seizure.  The shock lasts a mere second or two, but in those seconds the brain releases numerous chemicals, including neurotransmitters; the plentiful supply improves the brain's communication and weakens the depression. Side effects include short-term memory loss, muscle aches, headache, and temporary confusion.  ECT is usually administered several times a week, often supplemented by an antidepressant to prevent relapse; eventually, the treatments are reduced to once a week, and then monthly for up to a year. Research shows no sign of negative cognitive effects on patients after a year of electroconvulsive therapy. 
Besides therapy and medicine, depression can be simply treated by alterations in lifestyle. For example, daily exercise, a balanced diet, and plenty of sleep, all positively contribute towards a person's mental and physical well-being. Reducing stress and keeping socially active are also healthy lifestyle decisions that can lessen the impacts or occurrences of depression. Current research is investigating the effectiveness of relaxation techniques (like yoga, meditation, etc.) and acupuncture in treating forms of depression.  A popular natural remedy is St. John's Wort, a medicinal plant widely used in Europe to treat depression. Although this plant extract has been used for centuries, studies show conflicting results as to its effectiveness in treating depression; most conclude that it's useful in treating minor depression, but does little for major depression. Part of its popularity lies in its few side effects and various forms, from liquid extracts to tea and pills. 
In the U.S. alone, around 6 million men suffer from a form of depression every year. When men become depressed, they are more likely to admit a lack of interest in their hobbies or work, poor sleep, irritability, and fatigue, than express feelings of guilt or melancholy. Rather than seek medical attention when depression symptoms occur, many men resort to drugs or alcohol; they feel frustrated, angry, and sometimes become violent and abusive. Others immerse themselves in their work, trying to deny the depression to themselves as well as friends and family. Some men even become reckless, not caring how they drive or taking unnecessary risks. The connection between suicide and depression is also clearly seen. Men are four times as likely as women to take their own lives; this statistic could reflect how men often resist seeking proper treatment or receive incorrect diagnosis. 
Women are twice as likely as men to experience depression, and this disparity crosses all racial, economical, and ethnic boundaries worldwide; around one in eight women suffer from a depressive episode in their lifetime. Unlike men, women react to depression by excessive sleeping and eating (particularly carbohydrates), as well as weight gain. Guilty emotions and depression-related feelings are also more pronounced in women and they have a higher rate of thyroid problems. Researchers have developed many theories as to why women are especially vulnerable to depression. Premenstrual, pregnancy, and infertility problems contribute to major hormonal changes within the body, increasing a woman's risk for depression. Postpartum depression, or "baby blues", is a frequent condition in which a new mother temporarily experiences a form of depression, but this typically dissipates within a few weeks and only continues if the mother has severe and lasting depression. Premenopause and menopause also change the hormone levels in a woman's body and can induce depression, especially in those with a previous history of depression. Socially, the strain of playing various roles (worker, mother, wife) can put women at risk; single mothers are especially vulnerable. Discrimination in the workplace, low socioeconomic status, and society's continual emphasis on youth and beauty are other potential factors that can lead to depression in women. Men distract themselves when they're depressed, but women tend to hold onto their depression, discussing it with friends and trying to find the causes, which maintains or even worsens their condition. Women also develop depression even under low levels of stress because females have a hormone called progesterone that prevents the body from ceasing the production of stress hormones (men don't have progesterone.) Difficulties with self-esteem and relationships have significant impacts on the feminine mind, and both of these can trigger a depressive episode. 
Depression is not a part of the aging process, but it is a common occurrence. A study by the National Institutes of Health discovered that 7 million of the 35 million Americans 65 years or older struggle with some form of depression. Few receive the proper medical attention needed to treat this condition and many seniors are reluctant to seek help. Because of this, many seniors become involved in alcohol or substance abuse, increase their risk of illness, and die younger, some even resort to suicide.  In fact, the highest suicide rate is in Caucasian men age 85 and older, many with depression disorders. Older adults are at risk for depression because of other health conditions (like cancer, heart disease, strokes, etc.) and/or medications that have depression as a side effect.  Other potential causes are: isolation and loneliness (living alone, losing personal mobility), a lack of purpose or loss of personal identity (retirement, physical limitations), health issues (aged body image, chronic pain, natural decline, etc.), grief (loss of friends, family, or long-time spouse), and fear/anxiety (death, finances, health).  Thankfully, seniors that do receive treatment, usually through psychotherapy and/or antidepressants, show signs of recovery and periods free of depression. 
Depression in teenagers often accompanies the arrival of adolescence as they encounter hormonal, social, physical, and mental changes. Other adolescence-related issues that frequently co-occur with depression are eating and anxiety disorders.  It's estimated that only 20% of teens with depression receive treatment, most likely because they rely on their parents and other adults to look out for their welfare. Sometimes these adults have trouble identifying the difference in temporary moodiness and depression in teenagers, particularly since teens often struggle in articulating their feelings and their symptoms vary. Many become easily irritable and angry, although some become melancholy and withdrawn. Other symptoms in teenagers include: recurring aches and pains that seem to have no obvious medical cause, changing social groups or maintaining fewer friendships than before, and a heightened sensitivity to criticism.  Some factors influencing the rise in teen depression are the conflicting messages given by society and family, as well as feelings of failure and acute disappointment associated with unrealistic family or academic expectations. Recent studies discovered that one in five teenagers has clinical depression.  Untreated teen depression can lead to substance abuse, running away, poor performance in school, low self-esteem, internet addiction, eating disorders, violence, self-destructive behavior (cutting, burning, etc.), recklessness (drinking, dangerous driving, sexual promiscuity), and even suicide. Sadly, the third leading cause of teenage deaths is suicide, according to the Center for Disease Control. Common treatments for teen depression are "talk therapy" and antidepressants. 
Forms and Related Disorders
A chronic form of depression that lasts two years or longer, but has less severe symptoms than major depression; can prevent people from functioning normally without entirely disabling them. Dysthymic patients also are at risk for episodes of major depression throughout their life. 
Seasonal Affective Disorder (SAD)
A seasonal condition in which a person becomes depressed over the fall and winter months (though there is a rare form that occurs during the late spring and summer). Experts postulate that lower levels of sunlight during the winter reduce the serotonin production levels in the brain, resulting in SAD. In support of this, SAD is seldom present in countries within 30 degrees of the Equator where sunshine is year round. Craving for carbohydrates often accompanies this disorder because carbohydrates boost serotonin levels in the brain. SAD is most common in females and usually begins when they are young adults. Common symptoms include: trouble concentrating, increased fatigue and desire for sleep, lower levels of energy, sharpened appetite, and weight gain. Summer forms of SAD have the opposite effects, resulting in weight loss, a decrease in appetite, and trouble sleeping. Doctors treat SAD by recommending increased sunlight exposure, light therapy, and antidepressant medication. 
Up to 80% of new mothers experience some form of "baby blues" after giving birth, while in 10-20% of these cases the women develop postpartum depression. Women most at risk are those who've already had clinical depression, psychosocial stress, or who have poor social support. Symptoms include feelings of inadequacy (as a parent), increased incidents of crying, difficulty sleeping, and a lack of enjoyment in pleasurable activities. Worry over the baby's health and concentration problems are also signs of postpartum depression. This form of depression can even escalate to the point where the new mother contemplates suicide, as well as killing the baby (in an effort "not to abandon" them). The most serious form, postpartum psychosis, can induce delusions and hallucinations; mothers with this form are more likely to carry out harmful thoughts on themselves and/or their infants. Although no direct cause to postpartum depression has been found, the sudden drop of the female hormones progesterone, cortisol, and estrogen within 48 hours of birth is the most likely cause. Physical and emotional changes after birth also have a serious impact on new mothers. 
Although an entirely separate condition, bipolar disorder was once called maniac depression. Bipolar can induce serious mania, causing sleeplessness, psychosis, delusions, hallucinations, and rage, sometimes days at a time. Bipolar is also characterized by mood swings, dramatic or mild, that can gradually occur or change in a matter of minutes. People who suffer from this condition tend to have trouble thinking and socializing in a typical manner. Causes for bipolar disorder are unknown, though a genetic link has been established. The symptoms of bipolar disorder are very similar to major depression (fatigue, feelings of guilt or pessimism, chronic pain, suicidal thoughts/attempts, over or under eating, etc.) Bipolar disorder can be treated through mood stabilizing medications, antidepressants, anticonvulsants, antipsychotics, etc. 
- Depression.com © 1997-2009 GlaxoSmithKline.
- Depression National Institute of Mental Health.
- Men and Depression National Institute of Mental Health.
- Understanding Depression © 2001-2008. helpguide.org.
- Depression in Women © 2001-2008. helpguide.org.
- Depression in Older Adults and the Elderly © 2001-2008. helpguide.org.
- Teen Depression © 2001-2008. helpguide.org.
- Causes of Depression © 2005-2009. WebMD, LLC. webmd.com.
- Common Causes of Depression © 2005-2009 WebMD, LLC. webmd.com.
- Electroconvulsive and Other Depression Therapies © 2005-2009 WebMD, LLC. webmd.com.
- Depression Medicines © 2005-2009 WebMD, LLC. webmd.com.
- Seasonal Depression (Seasonal Affective Disorder) © 2005-2009 WebMD, LLC. webmd.com.
- Bipolar Disorder © 2005-2009 WebMD, LLC. webmd.com.
- How Does Depression Develop? 29 October 2008. "Medical Content Reviewed by the Faculty of Harvard Medical School."
- Depression Causes emedicinehealth.com. © 2009 WebMD, Inc.
- Postpartum Depression emedicinehealth.com. © 2009 WebMD, Inc.
- Psychotherapy for Depression Cleveland Clinic.
- Depression: Treatment With Electroconvulsive Therapy familydoctor.org. © 2000-2009 American Academy of Family Physicians.
- Definition of Selective serotonin reuptake inhibitor © 1996-2009 MedicineNet, Inc. MedicineNet.com.
- St. John's Wort and Depression National Center for Complementary and Alternative Medicine. National Institutes of Health.
- Factsheet: Depression in Teens © 2009 Mental Health America. mentalhealthamerica.net.
- Depression Facts and Statistics © 2009 depressionperception.com.
- Depression Facts, Prevention, and Treatment Strategies © 1999-2001 Personal Health Lifestyles, Inc. healingwithnutrition.com.
- Major Depression © 1996-2009 National Alliance on Mental Illness.
- Depression Information and Treatment© 1999, 2000, 2002, 2003. Psychology Information Online.
- Types of Depression: Definitions and Terminology © 2006-2007. Depression-help-resource.com.
- Seasonal Affective Disorder © 1996-2009 National Alliance on Mental Illness.
- Depression- Major Depression Treatment Studies © 2009 Stanford School of Medicine. Department of Psychiatry and Behavioral Sciences.
Other mental illnesses
- Alzheimer's disease
- Asperger syndrome
- Attention deficit hyperactivity disorder
- Bipolar disorder
- Bovine spongiform encephalopathy
- Bulimia nervosa
- Childhood amnesia
- Dissociative identity disorder
- Obsessive compulsive disorder
- Paranoid personality disorder
- Paranoid schizophrenia
- Personality disorder
- Posttraumatic stress disorder
- Walking corpse syndrome