Medicines used to treat clinical depression but that also may have beneficial effects when used to treat the chronic pain disorder fibromyalgia.

It is estimated that in any given year over 5% of Americans have clinical depression; the condition is even more common in people with chronic pain, such as that caused by arthritis. Depression is characterized by feelings of sadness, apathy, and worthlessness and may also include symptoms such as lack of sleep (or too much sleep), weight loss (or weight gain), decreased ability to concentrate, and lack of energy. In clinical depression, these symptoms last for at least two weeks and are serious enough to interfere with a person’s daily life. When used to treat depression, antidepressants have been shown to improve mood, increase concentration, diminish sleep and appetite problems, and raise energy levels. Antidepressants are often taken long-term; they usually require six to eight weeks to take effect. However, people may have to try several different antidepressants before finding one that works for them.

There are several types of antidepressants. Among the most common types are selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclics, and monoamine oxidase inhibitors (MAOIs). They work in different ways to increase the levels of chemicals called neurotransmitters in the brain. Depression is thought to be due in part to low levels of some of these neurotransmitters, such as serotonin and norepinephrine, though there is still much that remains unknown about the causes of depression. Of all antidepressants, SSRIs are the most frequently prescribed and include fluoxetine (brand name Prozac), paroxetine (Paxil), sertraline (Zoloft), and escitalopram (Lexapro). Common SNRIs are duloxetine (Cymbalta) and venlafaxine. At the moment, Duloxetine is one of only three drugs FDA-approved to treat the symptoms of fibromyalgia. (A doctor may prescribe other drugs mentioned in this article for fibromyalgia symptoms “off-label.”) Tricyclics were the first antidepressants and include amitriptyline, doxepin, and nortriptyline (Pamelor). And MAOIs, such as phenelzine (Nardil), are now generally prescribed only when other antidepressants have not worked.

Only in the last two decades or so have antidepressants found some use in the treatment of fibromyalgia, a chronic disorder that causes widespread pain and fatigue. People with fibromyalgia have low blood levels of serotonin and other neurotransmitters, and it is theorized that antidepressants, because they increase levels of one or more of these neurotransmitters, can relieve the symptoms of fibromyalgia. Antidepressants, especially tricyclics, may also induce drowsiness and can help people with fibromyalgia sleep better — trouble sleeping is a frequent symptom of fibromyalgia. People with fibromyalgia are often prescribed tricyclics, sometimes along with an SSRI. However, SNRIs are also sometimes prescribed, as well as other antidepressants that do not fit into the abovementioned categories. Examples of these include trazodone, bupropion (Wellbutrin, Zyban), and mirtazapine (Remeron). A small 2010 study found that about one-fifth of people taking trazofone for fibromyalgia experienced rapid heartbeat.

Antidepressants can have many side effects, which may be at their worst when the medicine is first taken but diminish over time. Tricyclics’ side effects can include dry mouth, temporary blurred vision, dizziness, and drowsiness. The newer antidepressants, SSRIs and SNRIs, can have side effects such as headache, nausea, nervousness, and insomnia. Side effects are often more pronounced in tricyclics than in the newer antidepressants. Antidepressants have also been shown to increase the risk of suicidal thoughts and behavior in children, adolescents, and young adults.

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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