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Selective Serotonin Reuptake Inhibitors (SSRIs): A Complete Guide

Katelyn Hagerty FNP

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 7/16/2020

Selective serotonin reuptake inhibitors, or SSRIs, are a common type of antidepressant. They’re typically prescribed to treat major depressive disorder (MDD, or depression), anxiety and other mood disorders, either on their own or in combination with psychotherapy.

If you’ve been diagnosed with depression, your healthcare provider may recommend using an SSRI to ease your symptoms and help you recover. You may also be prescribed an SSRI if you have a panic or anxiety disorder, or one of several other conditions.

SSRIs are some of the most common prescription medications in the United States, with tens of millions of users across the country.

Below, we’ve listed the most commonly prescribed SSRIs and explained how they work to treat depression and other conditions. We’ve also listed the most common side effects that you may experience if you’re prescribed an SSRI. 

Finally, we’ve answered some of the most common questions about SSRIs, from their safety to how long they usually take to start working, how to stop using them and more. 

Selective Serotonin Reuptake Inhibitors (SSRIs): An Overview

SSRIs are the most commonly prescribed medications used to treat depression. They’re often prescribed to treat moderate to severe depression.

The first SSRIs came onto the market in the late 1980s, making them a relatively new class of antidepressants. Many healthcare professionals use SSRIs as a first-line treatment for depression, as they tend to be less likely to cause severe side effects than older antidepressants. 

Although SSRIs are best known as treatment for depression, they’re also used to treat a diverse range of other conditions. SSRIs are prescribed for:

  • Generalized anxiety disorder (GAD)

  • Posttraumatic stress disorder (PTSD)

  • Obsessive compulsive disorder (OCD)

  • Social anxiety disorder (social phobia)

  • Premenstrual dysphoric disorder

  • Menopause symptoms, such as hot flashes

  • Eating disorders, such as bulimia and binge eating disorder

Some SSRIs are also prescribed for conditions such as fibromyalgia, irritable bowel syndrome (IBS) and premature ejaculation. Like other antidepressants, certain SSRIs are prescribed as a treatment for chronic pain conditions.

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How Selective Serotonin Reuptake Inhibitors (SSRIs) Work

SSRIs work by increasing the level of serotonin, an important neurotransmitter, that’s present in your brain.

Neurotransmitters are chemicals that are used by your brain to transmit signals between nerve cells, or neurons. Your body uses neurotransmitters to manage a range of biological functions, from your level of alertness and energy to your appetite, sleep quality, sex drive and more.

You may have heard serotonin referred to as the “happy chemical,” “happiness hormone” or something similar.

In reality, serotonin’s role in the body is complex. It plays a part in everything from your memory to your digestive system. It’s also responsible for regulating things such as your mood, feelings of anxiety, appetite and ability to sleep and wake up normally.

Experts believe that low levels of serotonin may contribute to depression, as well as some forms of anxiety. This is known as the “serotonin theory” of depression, and it’s backed up by research supporting the idea that some depressed people have reduced levels of serotonin.

SSRIs work by changing the way your brain deals with serotonin. Normally, your body’s neurons absorb serotonin after it’s received. SSRIs inhibit this process, meaning that more serotonin can circulate and come into contact with other neurons.

The result of this is an increase in serotonin levels that, for many people, can help to reduce the symptoms of depression and assist in recovery.

List of Selective Serotonin Reuptake Inhibitors (SSRIs)

Several SSRIs are currently available and in use. If you’ve been diagnosed with depression, an anxiety disorder or any other condition that’s treated using SSRIs, your healthcare provider may recommend one of the following medications:

  • Fluoxetine. Sold under the brand name Prozac®, fluoxetine was the first SSRI to come onto the market in 1987. We’ve explained how it works and more in our complete guide to fluoxetine.

  • Paroxetine. Sold under the brand name Paxil®, paroxetine was approved by the FDA in 1992. Our complete guide to paroxetine explains how it works, common dosages, side effects and more. 

  • Sertraline. Sold under the brand name Zoloft®, sertraline was first approved by the FDA in 1991. We’ve gone into more detail on how it works, side effects and more in our guide to sertraline.

  • Escitalopram. Sold under the brand name Lexapro®, escitalopram is a newer SSRI that was approved by the FDA in 2002. We’ve explained how it works and more in our guide to escitalopram.

  • Citalopram. Sold under the brand name Celexa®, citalopram was approved by the FDA in 1998. 

  • Fluvoxamine. Sold under the brand name Luvox®, fluvoxamine is typically used to treat obsessive-compulsive disorder (OCD) and social anxiety disorder (SAD). 

Of the SSRIs listed above, there’s no “best” medication for everyone. Your healthcare provider will choose a suitable SSRI or other antidepressant for you based on your symptoms, health and a range of other factors. 

Using Selective Serotonin Reuptake Inhibitors (SSRIs)

Almost all SSRIs come in tablet or capsule form. Most antidepressants of this class need to be taken either once or twice per day. If you’re prescribed an SSRI, follow the dosage instructions provided by your healthcare provider.

It can take several weeks for most SSRIs to start working. If you don’t notice any improvements after starting an SSRI, keep in contact with your healthcare provider. Over time, you may need to adjust your dosage or use a different type of medication.

Side Effects of Selective Serotonin Reuptake Inhibitors (SSRIs)

Although SSRIs are less likely to cause side effects than most older antidepressants, there are still several potential side effects that you should be aware of if you’re prescribed an SSRI.

Many side effects of SSRIs are transient and mild, meaning they’ll go away on their own as you get used to the medication. However, some side effects can be persistent. In rare cases, SSRIs can also cause serious, potentially harmful side effects.

Common side effects of SSRIs include:

  • Agitation

  • Anxiety

  • Blurred vision

  • Difficulty reaching orgasm

  • Dizziness

  • Nausea and vomiting

  • Reduced sex drive

Side effect rates can vary between different medications. For example, one study found that paroxetine (Paxil) has a higher risk of causing sexual side effects than many other SSRIs.

In men, certain SSRIs are also associated with erectile dysfunction. This is often treatable with ED medications, such as Viagra® (sildenafil), Cialis® (tadalafil) or Levitra® (vardenafil).

If you experience side effects after you start using any SSRI or other antidepressant, talk to your healthcare provider. Side effects from SSRIs generally improve over time without you needing to change your dosage or consider other medication. 

If you have severe or persistent side effects after starting an SSRI, your healthcare provider may recommend lowering your dosage or switching to a different medication. There are many antidepressants on the market, many of which may be less likely to cause common side effects for you. 

Selective Serotonin Reuptake Inhibitors (SSRIs) Safety

Overall, SSRIs are a safe, effective class of antidepressants that most people can use without any major safety concerns. However, there are several important safety-related things that you should be aware of before using any SSRI medication:

  • Like other medications, SSRIs can cause drug interactions. Some of these can be harmful, including interactions between SSRIs and other antidepressants, nonsteroidal anti-inflammatory drugs (NSAIDs) and other blood thinning medications.

    To avoid potentially hazardous drug interactions, make sure you tell your healthcare provider about all other medications you currently use or have recently used before using any SSRI. It also pays to check the specific interactions list for any medications you’re prescribed.

  • SSRIs can, in rare cases, cause serotonin syndrome. This is a dangerous condition in which SSRIs combine with other medications, raising the amount of serotonin in your body to a dangerous level.

    Serotonin syndrome often occurs when you use SSRIs at the same time as other drugs that affect serotonin levels, such as other antidepressants (particularly MAOIs), certain pain medications, certain migraine medications (like triptans) and anti-depression supplements such as St. John's wort.

  • SSRIs may not be safe to use if you’re pregnant or breastfeeding. Many SSRIs are pregnancy category C medications, meaning there’s limited data regarding their safety for use during pregnancy.

    If you’re prescribed an SSRI and think that you’re pregnant, or want to become pregnant in the near future, talk to your healthcare provider to work out a safe, effective treatment plan for you to follow during your pregnancy.

  • Antidepressants may increase suicide risk in teens and young adults. SSRIs, like other antidepressants, are sold with a warning from the FDA noting a potential increase in suicide risk for people 24 years of age and under.

    Although SSRIs are effective at reducing suicide risk in the long term, it’s important to be alert if you’re prescribed this type of medication. If you experience any changes in mood, suicidal thoughts or unusual behavior, seek immediate medical assistance.

  • Stopping SSRIs suddenly can cause withdrawal symptoms. As we’ve explained in more detail below, stopping certain SSRIs abruptly could cause withdrawal symptoms such as nausea, vomiting, mood swings, difficulty sleeping, tremors and more.

    These symptoms are classed as antidepressant discontinuation syndrome and occur in approximately 20 percent of patients after abrupt discontinuation of antidepressants.

    If you’re prescribed an SSRI and want to stop using it, talk to your healthcare provider before making any changes. They will likely advise you to gradually taper down your dosage to reduce your risk of experiencing withdrawal symptoms. 

Other Medications for Treating Depression

Thanks to their efficacy, convenience and reduced likelihood of causing side effects compared to older medications, SSRIs are a common first-line treatment for depression, anxiety disorders and other conditions, such as posttraumatic stress disorder (PTSD).

However, they’re far from the only medications available to treat depression. Other medications, such as serotonin–norepinephrine reuptake inhibitors (SNRIs) and tricyclic antidepressants, can also treat depression and help you to recover.

We’ve explained how these medications work, their side effects and more in our complete guide to medications for depression. 

Frequently Asked Questions About SSRIs

How Long Do SSRIs Take to Work?

SSRIs can be highly effective at treating depression and other mood disorders. However, the results usually aren’t immediate. Most people need to take SSRIs for several weeks or longer to experience their full effects on mood and depression symptoms.

If you’re prescribed an SSRI to treat depression, you may feel a mild improvement in your sleep and cognitive performance after using the medication for three weeks.

If you don’t feel any improvement in your mood and other depression symptoms after using your prescribed SSRI for eight weeks or longer, don’t stop taking your medication. Instead, reach out to your healthcare provider.

Depending on your symptoms and several other factors, your healthcare provider may recommend adjusting your dosage or switching to a different type of antidepressant. 

How Long Do You Need to Take SSRIs?

No two cases of depression are identical, meaning there’s no one-size-fits-all amount of time in which you’ll need to take SSRIs or other antidepressants.

As mentioned above, it can take several months before SSRIs and other antidepressants work fully to improve your mood and treat depression. Your healthcare provider may advise you to continue using your medication for six months or longer, even after you notice an improvement in your mood. 

Stopping use of SSRIs or other antidepressants too early may cause your depression to return or worsen. Follow the advice provided by your healthcare provider and continue using antidepressants for as long as necessary to fully treat your depression and recover. 

How Do SSRIs Work for Anxiety?

Although they’re typically used for depression, several SSRIs are commonly prescribed to treat certain anxiety disorders. For example, paroxetine (Paxil) and escitalopram (Lexapro) are both approved by the FDA to treat generalized anxiety disorder.

Numerous other SSRIs are approved to treat panic disorder, post-traumatic stress disorder and other related conditions. It’s also common for some SSRIs to be prescribed off-label for certain forms of anxiety. 

Although the exact role of serotonin in anxiety disorders isn’t fully understood, SSRIs may help to treat anxiety because of their effects on serotonin levels in the brain.

Do SSRIs Cause Weight Gain or Weight Loss?

Antidepressants, including SSRIs, have a reputation for causing weight gain. While it’s true that some people gain weight after starting antidepressants, many don’t, and not all antidepressants are equally likely to affect your weight and body composition. 

Most antidepressants associated with weight gain are older medications. Weight gain is quite a common side effect of some tricyclic antidepressants, as well as monoamine oxidase inhibitor medications such as phenelzine

Studies tend to suggest that paroxetine (Paxil) is significantly more likely to cause weight gain than other SSRIs. 

In a 2000 study, researchers found that paroxetine (Paxil) caused the most significant increase in weight over a 26 to 32 week period. The other SSRIs used in the study — sertraline (Zoloft) and fluoxetine (Prozac) — produced nonsignificant weight gain or loss of less than one percent of the patients’ starting body weight. 

Some SSRIs are also linked to weight loss. For example, two separate studies of fluoxetine — one from 1991 and another from 1999 — found that people prescribed fluoxetine lost a modest amount of weight while using this medication to treat depression. 

In short, there’s no simple, one-size-fits-all link between SSRIs and weight gain or loss. Certain SSRIs, such as paroxetine (Paxil), are associated with weight gain. However, many others don’t appear to have any significant effects on appetite, eating habits, metabolism or weight. 

If you’re worried about experiencing weight fluctuations after starting an SSRI or other antidepressant, make sure you let your healthcare provider know. They may be able to prescribe an antidepressant that isn’t likely to affect your weight or body composition. 

Are SSRIs Addictive?

SSRIs are not addictive. However, if you abruptly stop taking an SSRI or miss several doses of your medication in a row, you may experience withdrawal symptoms such as nausea, vomiting, mood swings, irritability, tremors, difficulty sleeping and unusual sensations. 

This is known as antidepressant discontinuation syndrome. To avoid experiencing withdrawal symptoms, it’s important to talk to your healthcare provider before stopping or adjusting your dosage of any SSRI. 

Are SSRIs Dangerous?

In general, SSRIs are safer and less likely to cause side effects than other, older antidepressant medications. However, like all medications, SSRIs still have certain risks.

All antidepressants, including SSRIs, feature an FDA “black box” warning that notifies users of an increased risk of suicidal thoughts and/or behavior. This elevated risk affects people under the age of twenty-four. It does not appear to affect adults above 24 years of age.

SSRIs may be dangerous if used with other medications, particularly medications that increase serotonin levels. If you’re prescribed an SSRI, make sure to check with your healthcare provider for drug interactions before using your medication. 

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Can You Drink Alcohol While Using SSRIs?

Drinking alcohol with antidepressants, including SSRIs, generally isn’t recommended. If you’re prescribed antidepressants to treat depression, drinking alcohol may cause your symptoms to become worse. It may also increase your risk of experiencing side effects.

Because of this, it’s best not to drink while you’re using any SSRI antidepressant. If you are a regular alcohol drinker, or have an alcohol use disorder, make sure that you inform your healthcare provider before using any type of antidepressant.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

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