Antidepressant

I

Introduction

Antidepressant, medication used to treat depression, a mood disorder characterized by such symptoms as sadness, decreased appetite, difficulty sleeping, fatigue, and a lack of enjoyment of activities previously found pleasurable. While everyone experiences episodes of sadness at some point in their lives, depression is distinguished from this sadness when symptoms are present most days for a period of at least two weeks. Antidepressants are often the first choice of treatment for depression.

II

How Antidepressants Work

Although the cause of depression is unknown, researchers have found that some depressed people have altered levels of neurotransmitters, chemicals that enable nerve cells to communicate. Too little activity among neurotransmitters in the areas of the brain that control mood and emotion is thought to contribute to depression.

Antidepressants interact with neurotransmitters in different ways. They can change the rate at which the neurotransmitters are either created or broken down by the body. They can block the process by which neurotransmitters are recycled and reused, a process called reuptake. By blocking reabsorption of neurotransmitters into the nerve cells, these antidepressants leave more of the neurotransmitter available to trigger activity among nerve cells. Finally, antidepressants can interfere with the binding of a neurotransmitter to neighboring nerve cells, thus leaving the neurotransmitter available.

III

Types of Antidepressants

The first antidepressants, developed in the 1950s, are the tricyclic antidepressants (TCA) and the monoamine oxidase (MAO) inhibitors. TCAs block the reuptake of three neurotransmitters: serotonin, norepinephrine, and dopamine. TCAs include the drugs amitriptyline, doxepin, imipramine, nortriptyline, and desipramine. Although TCAs are as effective as the antidepressants developed later, they have more unpleasant side effects.

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MAO inhibitors decrease the rate at which neurotransmitters are broken down by the body so they are more available to interact with nerve cells, or neurons. MAO inhibitors currently available in the United States include phenelzine and tranylcypromine.

A third group of antidepressants, known as selective serotonin reuptake inhibitors (SSRIs), became available in 1987. SSRIs block the reuptake of the neurotransmitter serotonin, thereby prolonging its activity. There are currently a number of SSRIs available for use in the United States, including fluoxetine, sertraline, paroxetine, and citalopram. Of this group, the best known is fluoxetine, commonly known by its brand name, Prozac. Sertraline is sold as Zoloft, paroxetine as Paxil, and citalopram as Celexa. Although all SSRIs work the same way, they have different side effects.

Newer groups of antidepressants regulate the levels of serotonin and an additional neurotransmitter. The best-known serotonin and norepinephrine reuptake inhibitor (SNRI) is venlafaxine, which is sold as Effexor. Bupropion, sold as Wellbutrin, is a serotonin and dopamine reuptake inhibitor (SDRI). Tetracyclic antidepressants prevent the neurotransmitters serotonin and norephinephrine from binding to nearby nerve cells. Mirtazapine, sold as Remeron, is a tetracyclic antidepressant.

Dual-action antidepressants work in two ways, by blocking reuptake and by preventing neurotransmitters from binding to neurons. These drugs include nefazodone, trazodone, and maprotiline. But they are rarely prescribed because of their serious side effects.

IV

Effectiveness and Side Effects

All antidepressants decrease symptoms of depression in about 70 percent of depressed people who take them. With most antidepressants, three weeks or more of treatment is necessary before beneficial effects occur. Although no antidepressant is more effective overall in treating depression than the others, some people respond better to one drug than to another, and they may have to try more than one before finding the most beneficial drug.

Doctors also decide which antidepressant to prescribe according to the type of side effects an individual can tolerate. For instance, a person who takes TCAs and MAO inhibitors may notice dizziness and fainting when standing up, mouth dryness, difficulty urinating, constipation, and drowsiness. If people who take MAO inhibitors eat certain foods, such as aged cheese or some aged meats, they can experience severe headaches and raised blood pressure. SSRIs can cause side effects such as restlessness, difficulty sleeping, and interference with sexual function.

Awareness of the side effects associated with a drug is important. People who suffer from insomnia will want to avoid an antidepressant associated with difficulty sleeping. It is also important for patients on antidepressants to report any other medical conditions they have or drugs they are taking to the prescribing physician. Certain antidepressants, for example, carry a risk of liver problems. Some antidepressants cannot be combined with certain other drugs. Some should not be taken by pregnant women.

In 2007 a Canadian study reported that people over 50 who take SSRIs have twice the risk of sustaining a bone fracture as people not taking these drugs. SSRIs appear to increase the risk of falls. They also have some effect on bone formation, so it is a wise idea for people on these drugs to exercise and increase calcium and vitamin D intake to help combat the risk of fracture.

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