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Selective Serotonin Reuptake Inhibitors (SSRIs): A Complete Guide

Kristin Hall, FNP

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 2/1/2022

If you’ve been diagnosed with depression, your healthcare provider may prescribe you a type of medication called a selective serotonin reuptake inhibitor, or SSRIs.

SSRIs are a common class of antidepressants. They’re used to treat major depressive disorder (MDD, or clinical depression), as well as a variety of anxiety disorders and other mental health 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 antidepressants that are commonly used to treat depression. Today, they’re the most commonly used medications for depression and are typically prescribed as a first-line treatment for several psychiatric disorders.

The first SSRIs came onto the market in the late 1980s, making them a relatively new treatment option for depression. Today, SSRIs are favored by many healthcare providers for their low risk of causing side effects when compared to older medications for depression.

Although SSRIs are best known as a 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 

  • Treatment-resistant depression

  • Bipolar depression

  • 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 may be prescribed to treat chronic pain conditions. 

How Do Selective Serotonin Reuptake Inhibitors Work?

SSRIs work by inhibiting the reuptake of serotonin, a vital neurotransmitter that’s active in your brain and body. This effect on serotonin reuptake increases total serotonin levels.

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 change in your brain chemistry is an increase in serotonin levels that, for many people, can help to reduce the symptoms of depression and assist in recovery.

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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. Our guide to fluoxetine (Prozac) explains how this medication works, what it’s prescribed for, its side effects and more.

  • 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, potential 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, potential side effects and more in our guide to escitalopram (Lexapro).

  • 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 another antidepressant for you based on your symptoms, health and a range of other factors.

How To Use 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 any type of SSRI to treat depression or anxiety, make sure to closely follow the instructions provided by your healthcare provider. 

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

It’s normal to try several SSRIs before finding one that works best for you. Don’t be afraid to tell your healthcare provider if you feel that your medication isn’t working effectively, or that it might not be the best option for treating your specific depression or anxiety symptoms.

 Side Effects of Selective Serotonin Reuptake Inhibitors (SSRIs)

SSRIs are usually well tolerated. In fact, one of the major reasons they’re prescribed more often than older medications is that they’re less likely to cause side effects. This may be due to their more targeted action on serotonin instead of other important neurotransmitters.

Although SSRIs are less likely to cause side effects than older types of antidepressants, it’s still possible for side effects to occur. 

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 adverse effects of SSRIs include:

  • Sleep disturbances (difficulty sleeping or staying asleep)

  • Changes in appetite and weight gain or weight loss

  • Sexual dysfunction, including changes in sexual desire

  • Anorgasmia (difficulty reaching orgasm and ejaculation)

  • Gastrointestinal disturbances

  • Dizziness and/or headache

  • Xerostomia (dry mouth caused by lack of saliva)

Side effect rates can vary between different medications. For example, some research suggests that paroxetine (Paxil) has a higher risk of causing sexual side effects than other SSRIs used to treat depression and anxiety disorders.

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 often improve over time without you needing to change your dosage or consider other medication. 

However, 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.

Switching antidepressants is common and normal. There are many different antidepressants available on the market, some of which may be more able to treat your depression or anxiety symptoms without side effects than others.

Selective Serotonin Reuptake Inhibitors (SSRIs) Safety

For most people, SSRIs are safe and effective medications that successfully treat depression and anxiety disorders without any major safety concerns. 

However, there are several important safety-related issues that you should be aware of before using any SSRI medication.

Safety During Pregnancy

SSRIs may not be safe to use if you’re pregnant or breastfeeding. Certain SSRIs are associated with an increase in transient neonatal complications (complications that can occur after birth and may require clinical care).

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 and effective treatment plan for you to follow during your pregnancy.

Suicide Risk in Teens and Young Adults

Antidepressants may increase suicide risk in teens and young adults. SSRIs, like other common 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 your mood, suicidal thoughts or unusual behavior, seek immediate medical assistance.

Withdrawal Symptoms

SSRIs are safe and effective for most people when used correctly. However, stopping treatment with an SSRI abruptly may cause a range of withdrawal symptoms referred to as antidepressant discontinuation syndrome.

These symptoms may include nausea, vomiting, mood swings, difficulty falling asleep or staying asleep, tremors and other issues. Discontinuation symptoms occur in approximately 20 percent of patients after abrupt discontinuation of antidepressants.

If you’re prescribed an SSRI for depression, anxiety or any other condition and no longer wish to use it, talk to your healthcare provider before making any changes. 

Your healthcare provider will likely advise you to gradually taper down your dosage to lower your risk of experiencing withdrawal symptoms.

SSRI Drug Interactions

Like other medications, SSRIs can potentially result in interactions when used with certain other medications. Some of these can be harmful, including potential interactions between SSRIs and certain prescription medications and over-the-counter substances.

To avoid potential 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’s also important to carefully read the specific interactions list for any medications you currently use before starting treatment for depression or anxiety with an SSRI.

Serotonin Syndrome

SSRIs can, in rare cases, cause serotonin syndrome. This is a dangerous condition in which the serotonin-increasing effects of SSRIs are combined with those of other medications, resulting in a significant increase in serotonin levels that can potentially be life threatening.

Serotonin syndrome can occur when SSRIs are used at the same time as medications that can also increase serotonin levels. These include:

  • Other antidepressants, including other SSRIs, SNRIs, tricyclic antidepressants (TCAs), buspirone and monoamine oxidase inhibitors (MAOIs).

  • Opiate painkiller medications, including tramadol, other opioid medications and illegally produced opioid drugs.

  • Certain triptans, antipsychotic medications, antibiotics, anti-anxiety drugs and common medications used to treat migraines, headaches and infections.

  • Over-the-counter products and herbal supplements that increase serotonin levels, such as St. John’s wort.

To reduce your risk of developing serotonin syndrome, it’s important to discuss any medications you currently use or have recently used with your healthcare provider. 

Are SSRIs Effective?

SSRIs are effective for many people with depression. However, it’s difficult to predict how well a person with depression will respond to antidepressants -- or a specific type of antidepressant -- before they begin treatment.

Most research shows that SSRIs are effective for moderate and severe forms of depression, but less effective for mild depression.

In studies of adults affected by moderate or severe depression, approximately 40 to 60 percent of people who took an antidepressant experienced improvements in their symptoms after six to eight weeks of treatment.

In comparison, approximately 20 to 40 percent of people experienced improvements during the same time period after taking a non-therapeutic placebo.

In short, SSRIs and other antidepressants are effective, but not always for everyone affected by depression. While many people experience significant improvements, others may not notice an effect from SSRIs or other medications used to treat depression. 

In some cases, you may need to use several antidepressants, or a combination of medications and other forms of treatment, before finding the best way to reduce your depression symptoms and make progress towards recovery. 

Other Medications for Treating Depression

Thanks to their efficacy, convenience and reduced likelihood of causing side effects compared to older medications, SSRIs are common first-line treatments 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.

Our full list of antidepressants explains how these medications work, their side effects and how they’re often used to treat depressive illnesses.

Frequently Asked Questions About SSRIs

How Long Do SSRIs Take to Work?

SSRIs are often a successful treatment for depression and other mental disorders. However, the results of SSRIs usually aren't immediate. It may take up to six weeks for certain SSRIs to begin working, and the beneficial effects may develop gradually.

If you’re prescribed an SSRI or other antidepressant, you may notice that your sleep, appetite or other symptoms improve before you experience any changes in your mood.

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, it’s best to reach out to your healthcare provider.

Based on your symptoms and 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 begin to improve your mood and treat depression. Your healthcare provider may recommend that you continue using your medication even after you notice improvements in your symptoms.

Stopping use of SSRIs or other antidepressants too early may cause your depression to return or become worse. Follow the advice provided by your healthcare provider and continue using your 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, escitalopram (Lexapro) is 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 certain tricyclic antidepressants, as well as monoamine oxidase inhibitor medications such as phenelzine.

Not all SSRIs are linked with weight gain. Research tends 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. Some SSRIs, such as paroxetine (Paxil), are associated with weight gain. However, many others are not associated with any significant effects on appetite, eating habits, metabolism or weight.

If you’re concerned about experiencing weight fluctuations after starting treatment with an SSRI or other antidepressant, make sure you let your healthcare provider know. They may be able to prescribe an antidepressant that’s less likely to affect your weight or body composition.

Are SSRIs Addictive?

SSRIs are not addictive, habit-forming medications. However, abruptly stopping treatment with an SSRI or other antidepressant can potentially cause you to experience withdrawal symptoms referred to as antidepressant discontinuation syndrome. 

To avoid experiencing withdrawal symptoms, it’s important to talk with 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. To reduce your risk of drug interactions, inform your healthcare provider about all medications you currently use, both prescription and over the counter,  or have recently used before taking any type of SSRI. 

Can You Drink Alcohol While Using SSRIs?

Drinking alcohol with antidepressants, including SSRIs, generally isn’t recommended. Drinking while taking an antidepressant may increase your risk of developing side effects or cause your depression symptoms to become more severe. 

Make sure to check the drug label for any medication you use before consuming alcohol. If you are a frequent alcohol drinker, or have an alcohol use disorder, inform your healthcare provider before using any type of antidepressant. 

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Learn More About Taking SSRIs

SSRIs are the most common antidepressant drugs for treating depression. They’re also widely used to treat anxiety disorders, such as generalized anxiety disorder, panic disorder and social anxiety disorder.

Used as prescribed, SSRIs can help you to gain more control over your thoughts, feelings and behavior, allowing you to recover from depression or anxiety. 

We offer several SSRIs online via our online psychiatry service, following a consultation with a licensed provider who will determine if a prescription is appropriate.

You can also learn more about overcoming depression using our free mental health resources and detailed guide to depression treatments

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Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

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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.