Antidepressants are the first line of treatment for depression. Annual sales of antidepressants are approximately $50 billion, making this class of drugs one of the leading prescription medications. Many pharmaceutical companies engage in direct-to-consumer marketing of antidepressants through television and print media. So, patients have a large influence on the prescribing patterns of health-care providers when it comes to antidepressants. Antidepressants are commonly prescribed, but what are they, exactly? How do they work? Are they effective?

Joe Raedle/Getty Images Antidepressants are among the most prescribed medications in the United States.

In this article, we will examine depression, the types of antidepressant therapy, how antidepressants work, and their effectiveness and side effects. But to understand how antidepressants work, we first need to look at depression itself.

Medical Disclaimer This article is intended for information purposes only and not as medical advice. Those seeking medical advice regarding the diagnosis and treatment of depression should consult with your primary care provider and/or pharmacist.

Depression or Major Depressive Disorder (MDD, also called unipolar depression or clinical depression) occurs in about 15 million Americans in any given year. It can occur at any age (including in children as young as 5), but it most commonly affects 25- to 44-year-olds. MDD affects approximately 20 percent of women and 10 percent of men [source: HealthyPlace.com]. MDD leads to loss of productivity in the workplace and at school. Most importantly, it is a leading cause of suicide.

MDD, in contrast to short periods of the "blues," is a persistent change in mood that can interfere with family, relationships and feelings of self-worth. Recurrent episodes can last for days, months or years. MDD has physical and mental symptoms, which include the following:

• Depressed mood (sadness)
• Loss of interest or pleasure
• Disruptions of sleep patterns
• Fatigue
• Feelings of worthlessness, discouragement,
  hopelessness and helplessness
• Changes in appetite, weight loss or gain
• Loss of sexual interest
• Inability to think, concentrate or make decisions

For a clinical diagnosis of MDD, these symptoms must occur consistently for at least a two-week period.

You might notice that these symptoms can also be symptoms of other diseases (like hypertension, diabetes, heart disease and epilepsy). So, it's possible that the depressive episode is a secondary symptom of another disease. Because there is no lab test for depression, doctors may run many tests to rule out these other possible diseases. If everything else can be ruled out, what remains is MDD.

On the next page, we'll learn about what causes depression.

Video Gallery: Beating Depression Exercise has numerous effects on the body and mind, but some doctors think it can be effective in fighting depression. Learn about exercise and depression in this video from ScienCentral.

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