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What are mood disorders?

Mood disorders, sometimes called affective disorders, refer to a category of mental health problems that include all types of depression and bipolar disorder.

The following are the most common types of mood disorders:

  • Major depression—A two-week period of a depressed or irritable mood or a noticeable decrease in interest or pleasure in usual activities, along with other signs of a mood disorder.
  • Dysthymia (dysthymic disorder)—A chronic, low-grade, depressed or irritable mood for at least one year.
  • Manic depression (bipolar disorder)—At least one episode of a depressed or irritable mood and at least one period of a manic (persistently elevated) mood.
  • Mood disorder due to a general medical condition—Many medical illnesses (including cancer, injuries, infections and chronic medical illnesses) can trigger symptoms of depression.
  • Substance-induced mood disorder—Depression that is due to the effects of medication, drug abuse and/or exposure to toxins.


Depending upon the person’s age and the type of mood disorder present, a person may exhibit different symptoms of depression, including:

  • Persistent feelings of sadness
  • Feeling hopeless or helpless
  • Low self-esteem
  • Feelings of inadequacy
  • Excessive guilt
  • Loss of interest in usual activities or activities once enjoyed
  • Difficulty with relationships
  • Sleep disturbances (i.e., insomnia, hypersomnia)
  • Changes in appetite or weight
  • Decreased energy
  • Difficulty concentrating
  • A decrease in the ability to make decisions
  • Suicidal thoughts or attempts
  • Frequent physical complaints (e.g., headache, stomach ache, fatigue)
  • Running away or threats of running away from home
  • Hypersensitivity to failure or rejection
  • Irritability, hostility, aggression


What causes mood disorders is not well known. There are chemicals in the brain, called endorphins, which are responsible for positive moods. Other chemicals in the brain, called neurotransmitters, regulate endorphins. Most likely, depression and other mood disorders are caused by an imbalance of these chemicals in the brain. Life events (such as unwanted changes in life) may also contribute to mood disorders.

Mood disorders aggregate in families and are considered to be multifactorially inherited. Multifactorial inheritance means that many factors are involved in the process of an individual inheriting a mood disorder. The factors that produce the trait or condition are usually both genetic and environmental, involving a combination of genes from both parents. Often one gender is affected more frequently than the other in multifactorial traits. There appears to be a different threshold of expression, which means that one gender is more likely to show the problem than the other gender.

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