Mayo Clinic Health Library

Selective serotonin reuptake inhibitors (SSRIs)

Updated: 07-09-2013

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants. They can ease symptoms of moderate to severe depression, are relatively safe and generally cause fewer side effects than other types of antidepressants do.

How SSRIs work

SSRIs ease depression by affecting naturally occurring chemical messengers (neurotransmitters), which are used to communicate between brain cells. SSRIs block the reabsorption (reuptake) of the neurotransmitter serotonin in the brain. Changing the balance of serotonin seems to help brain cells send and receive chemical messages, which in turn boosts mood.

Most antidepressants work by changing the levels of one or more of these neurotransmitters. SSRIs are called selective because they seem to primarily affect serotonin, not other neurotransmitters.

SSRIs approved to treat depression

SSRIs approved by the Food and Drug Administration (FDA) to treat depression, with their generic names followed by brand names in parentheses, include:

  • Citalopram (Celexa)
  • Escitalopram (Lexapro)
  • Fluoxetine (Prozac)
  • Paroxetine (Paxil, Pexeva)
  • Sertraline (Zoloft)

Paxil CR is an SSRI that provides controlled release of the medication throughout the day or for a week at a time with a single dose.

SSRIs also may be used to treat conditions other than depression, such as anxiety disorders.

Side effects and cautions

All SSRIs work in a similar way and generally cause similar side effects. However, each SSRI has a different chemical makeup, so one may affect you a little differently than another. Most side effects may go away after the first few weeks of treatment, but talk to your doctor if any side effects are too troublesome for you.

Side effects of SSRIs may include, among others:

  • Nausea
  • Nervousness, agitation or restlessness
  • Dizziness
  • Reduced sexual desire or difficulty reaching orgasm or inability to maintain an erection (erectile dysfunction)
  • Drowsiness
  • Insomnia
  • Weight gain or loss
  • Headache
  • Dry mouth
  • Vomiting
  • Diarrhea

Taking your medication with food may reduce the risk of nausea. Also, as long as your medication doesn't keep you from sleeping, you can reduce the impact of nausea by taking it at bedtime.

Read the package insert for additional side effects, and talk to your doctor or pharmacist if you have questions.

Safety concerns

SSRIs are relatively safe. However, here are some examples of safety issues to be considered:

  • Antidepressants and pregnancy. Some antidepressants may harm your child if you take them during pregnancy or while you're breast-feeding. Paroxetine (Paxil, Pexeva) in particular appears to increase the risk of birth defects, including heart and lung problems. If you're taking an antidepressant and you're considering getting pregnant, talk to your doctor or mental health provider about the possible dangers. Don't stop taking your medication without contacting your doctor first.
  • Drug interactions. When taking an antidepressant, be sure to tell your doctor about any other medications or dietary supplements you're taking. Some antidepressants can cause dangerous reactions when combined with certain medications or herbal remedies.
  • Abnormal bleeding. Use of some pain relievers, such as aspirin, ibuprofen (Advil, Motrin IB, others) or naproxen sodium (Aleve, others), or anticoagulants, such as warfarin (Coumadin), may increase the risk of bleeding when combined with SSRIs. Talk to your doctor about the risks of using these medications in combination.
  • Serotonin syndrome. Rarely, an SSRI can cause dangerously high levels of serotonin. This is known as serotonin syndrome. It occurs when two medications that raise serotonin are combined. These include other antidepressants, certain pain or headache medications, and the herbal supplement St. John's wort. Signs and symptoms of serotonin syndrome include anxiety, agitation, sweating, confusion, tremors, restlessness, lack of coordination and rapid heart rate. Seek immediate medical attention if you have any of these signs or symptoms.

Suicide risk and antidepressants

Most antidepressants are generally safe, but the FDA requires that all antidepressants carry black box warnings, the strictest warnings for prescriptions. In some cases, children, teenagers and young adults under 25 may have an increase in suicidal thoughts or behavior when taking antidepressants, especially in the first few weeks after starting or when the dose is changed.

Anyone taking an antidepressant should be watched closely for worsening depression or unusual behavior. If you or someone you know has suicidal thoughts when taking an antidepressant, immediately contact your doctor or get emergency help.

Keep in mind that antidepressants are more likely to reduce suicide risk in the long run by improving mood.

Stopping treatment with SSRIs

SSRIs aren't considered addictive, but sometimes physical dependence, which is different from addiction, can occur. So stopping treatment abruptly or missing several doses can cause withdrawal-like symptoms. This is sometimes called discontinuation syndrome. Work with your doctor to gradually and safely decrease your dose.

Withdrawal-like symptoms can include:

  • Nausea
  • Dizziness
  • Lethargy
  • Flu-like symptoms

Finding the right antidepressant

Each person may react differently to a particular antidepressant and may be more susceptible to certain side effects. Because of this, one antidepressant may work better for you than another, or your doctor may prescribe a combination.

When choosing an antidepressant, your doctor will take into account your particular symptoms, what health problems you have, what other medications you take, what has worked for you in the past and what has worked for a close relative with depression.

Inherited traits play a role in how antidepressants affect you. In some cases, where available, results of special blood tests may offer clues about how your body may respond to a particular antidepressant. The study of how genes affect a person's response to drugs is called pharmacogenomics. However, other variables besides genetics can affect your response to medication.

Typically, it may take several weeks or longer before an antidepressant is fully effective and for initial side effects to ease up. You may need to try several dose adjustments or different antidepressants before you find the right one, but hang in there. With patience, you and your doctor can find a medication that works well for you.