Selective Serotonin Reuptake Inhibitors (SSRIs)

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Selective Serotonin Reuptake Inhibitors (SSRIs)




Recommended dosage


Side effects




Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressant medicines that help increase the activity of a chemical in the brain called serotonin. They are also called serotonin boosters.


Serotonin is a neurotransmitter, which is a substance that helps send messages between nerves in the brain. It is believed that problems with serotonin levels play a role in determining a person’s mood and behavior.

SSRIs are used to treat a wide variety of mental disorders, including:

  • major depressive disorder
  • obsessive-compulsive disorder
  • posttraumatic stress disorder (PTSD)
  • social and generalized anxiety
  • panic disorder
  • postmenstrual dysphoric disorder (PMDD)

Sometimes, a health-care provider will prescribe an SSRI for a condition other than the approved ones listed on the drug’s label. This is called off-label use. Off-label uses for SSRIs include the treatment of obesity, certain types of irritable bowel syndrome (IBS), and bulimia, an eating disorder. The American Medical Association has reported that SSRI use in persons with depression who have had a heart attack reduces the risk of death and repeated heart attacks.


SSRIs act on the central nervous system. They prevent nerve cells in the brain, called receptors, from

soaking up serotonin. The action of soaking up, or absorbing, a substance is called reuptake. When serotonin reuptake is blocked, the serotonin has nowhere to go, and the levels of the chemical in the brain increase. SSRIs were released in the U.S. market in 1987. Fluox-etine (Prozac) was the first type of SSRI sold in the United States. Ten years later, more than half of Americans receiving outpatient treatment for major depression were prescribed an SSRI.

SSRIs include:

  • citalopram (Celexa)
  • escitalopram (Lexapro)
  • fluoxetine (Prozac)
  • fluvoxamine (Luvox)
  • paroxetine (Paxil)
  • sertraline (Zoloft)

Recommended dosage

SSRIs are taken by mouth. They are available in many different forms. Extended-release (XR) and con-trolled-release (CR) forms slowly release medicine into the body over several hours. Most SSRIs are taken once a day. The exact dosage needed depends on the specific drug, the person’s age, and medical condition being treated. The medicine must be taken regularly for several weeks before an effect is seen. If symptoms continue, a different type of medicine may be prescribed.


Pregnant women

Pregnant women should discuss the use and safety of SSRIs with their health care providers. In 2006, the U.S. Food and Drug Administration (FDA) warned that mothers who take SSRIs after the 20th week of pregnancy have an increased risk of giving birth to babies with a serious heart and lung disorder called persistent pulmonary hypertension (PPHN). The FDA classifies a drug according to how it may affect a baby during pregnancy and breastfeeding. Most SSRIs fall into pregnancy category C, which means: 1) no animal and human studies have been done, or 2) animal studies have shown the drugs cause harm to a fetus, but more complete human studies are needed. The SSRI paroxetine (Paxil) falls into a higher risk category. The American College of Obstetricians and Gynecologists has recommended that pregnant women avoid taking Paxil. The organization encourages patients and doctors to carefully weigh the possible risk of birth defects against a woman’s individual risk of depression during pregnancy.

Children and young adults

Sometimes SSRIs may make depression worse or cause suicidal thoughts or behaviors. A government review of all studies involving antidepressant use among children and adolescents concluded that 4% of those taking SSRIs thought about suicide or displayed suicidal behavior. In October 2004, the FDA told the manufacturers of antidepressants that they must include a warning on the medicine’s label that tells users the drugs have been linked to an increase in suicide in children and young adults. Such an alert is called a “black box warning.” According to the FDA, the use of SSRIs among people aged 10 to 19 has risen sharply in recent years. Children and adolescents taking any type of antidepressants should be closely watched for signs of suicidal tendencies, behavior changes, or worsening of depression.

Other medical conditions

SSRIs should be used with caution in people with kidney or liver problems and diabetes, and in women who are producing breast milk (lactating).

Side effects

Side effects depend on the specific type of SSRI, but those most commonly reported are listed below:

Central nervous system


  • dizziness
  • drowsiness
  • headache
  • light-headedness
  • nervousness
  • tremors
  • trouble sleeping


  • itching
  • rash
  • sweating

Gastrointestinal system

  • anorexia nervosa (an eating disorder)
  • changes in taste
  • constipation
  • diarrhea
  • dry mouth
  • indigestion
  • nausea and vomiting

Reproductive system

  • painful menstruation
  • changes in sexual function, such as difficulty becoming aroused or reaching orgasm

Respiratory system

  • sore throat
  • upper respiratory infections


Forgetting to take several doses or stopping the drug suddenly can cause symptoms of withdrawal, which may include a flu-like feeling, nausea, headache, dizziness, and tiredness.


Taking SSRIs together with other drugs that affect serotonin levels, such as monoamine oxidase inhibitors (MAOIs) or tricyclic antidepressants, can lead to a rare but life-threatening drug reaction called “serotonin syndrome.” Symptoms of serotonin syndrome occur within minutes to hours, and may include high blood pressure, mental status changes, and increased body temperature (hyperthermia).

Taking SSRIs with the herbal remedy St. John’s wort may also cause this reaction.

SSRIs may slow down the body’s metabolism of many other drugs. The following drugs have also been reported to interact with SSRIs and, when taken together, may lead to dangerously high serotonin levels:

  • antipsychotics
  • benzodiazepines
  • beta-blockers
  • calcium channel blockers
  • cocaine
  • codeine
  • dextromethorphan
  • fenfluramine
  • levodopa
  • pentazocine



Kasper, Dennis L. Harrison’s Principles of Internal Medicine.16th ed. New York, NY: McGraw-Hill, 2005.


Metabolism —A series of chemical changes that break down food, medicine, and body tissue.

Monoamine oxidase inhibitor (MAOI) —An older type of antidepressant medicine.

Neurotransmitter —A substance that helps send messages between nerve cells.

Persistent pulmonary hypertension (PPHN) —A life-threatening disorder seen in newborn babies in which blood does not properly enter the lungs.

Tricyclic antidepressant (TCA)—An older group of antidepressants that were introduced in the 1960s. TCAs affect the activity of serotonin and another body chemical called norepinephrine.

Karch, Amy M. 2007 Lippincott’s Nursing Drug Guide.

Baltimore, MD: Lippincott Williams & Wilkins, 2007. Marx, J. Rosen’s Emergency Medicine: Concepts and Clinical

Practice. 6th ed. St. Louis, MO: Mosby, 2006.


Mental Health America, 2000 N. Beauregard Street, 6th Floor. Alexandria, VA 22311. (800) 969-6MHA (6642).

National Alliance on Mental Illness, 2107 Wilson Boulevard, Suite 300, Arlington, VA 22201-3042. (703) 524-7600.

National Institute of Mental Health, 6001 Executive Boulevard, Room 8184, MSC 9663, Bethesda, MD 20892-9663. (301) 443-4513.

Kelli Miller Stacy

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Selective Serotonin Reuptake Inhibitors (SSRIs)

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