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SSRI vs. SNRI: How They Work & Key Differences 

SSRI vs. SNRI: How They Work & Key Differences 
Reviewed by:
Authored by:
Glenn Occhiogrosso, MD
Staff Psychiatrist
at Talkiatry
August 29, 2023
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Whether you’re already taking antidepressants or are curious about different treatment options for depression, you may have come across the two most common types of antidepressants: SSRIs and SNRIs.

So what is the difference between the two? How do they work and how do you know which one might be right for you?  

In this article, we’ll cover how the two types of antidepressants work, how they differ from each other, and how to know which one is right for you.  

What are SSRIs?

SSRIs (AKA selective serotonin reuptake inhibitors) are the most commonly prescribed antidepressants. They’re a class of medications that work to reduce symptoms of depression by increasing the levels of serotonin (the “feel-good” hormone that helps regulate mood) in the brain.

Some examples of SSRIs include:

  • Citalopram (Celexa)
  • Escitalopram (Lexapro)
  • Fluoxetine (Prozac, Sarafem, Symbyax)
  • Fluvoxamine (Luvox, Luvox CR)
  • Paroxetine (Paxil, Paxil CR, Pexeva)
  • Sertraline (Zoloft)

How do SSRIs work?  

Serotonin is a chemical messenger (AKA a neurotransmitter) that helps control your mood, sleep, sex drive, digestion, and other important functions in the body. Normally, after serotonin sends a signal to your nervous system, it gets taken up by your cells and removed from circulation. SSRIs work by preventing some of the serotonin from being removed from circulation. Now, more of it is available to help send signals to your nervous system.  

You can also think of SSRIs as medications that ‘make sure serotonin is where it needs to be.’

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Conditions SSRIs can treat

Although SSRIs are classified as an antidepressant, they are also used to treat a wide range of mental physical health conditions including:  

  • Obsessive-compulsive disorder (OCD)
  • Panic disorder
  • Post-traumatic stress disorder (PTSD)
  • Premenstrual dysphoric disorder (PMDD)
  • Generalized anxiety disorder (GAD)
  • Major depressive disorder (MDD)
  • Bulimia
  • Fibromyalgia
  • Hot flashes

Possible side effects of SSRIs  

As with any medication, SSRIs can come with side effects. That’s why it’s important to take them only as directed and work with your licensed prescriber to select a dose that’s right for you. For most people, side effects (if any) will be mild and will go away as the body adjusts to the medication. But if side effects persist or are bothersome, let your prescribing physician know.  

Some common side effects can include:  

  • Feeling agitated, shaky or anxious
  • Nausea or vomiting
  • Indigestion
  • Diarrhea or constipation
  • Loss of appetite and weight loss
  • Dizziness  
  • Blurred vision
  • Dry mouth
  • Excessive sweating
  • Sleeping problems (insomnia) or drowsiness
  • Headaches
  • Loss of libido (reduced sex drive)
  • Difficulty achieving orgasm during sex or masturbation
  • Erectile disfunction in men

There are also less common side effects of SSRIs, which can include:  

  • Suicidal ideation
  • Worsening depression
  • Mania or hypomania
  • Confusion
  • Movement problems
  • Hallucinations
  • Being unable to pee
  • Bruising or bleeding easily
  • Vomiting blood or rectal bleeding
  • Serotonin syndrome

Serotonin syndrome

Serotonin syndrome, though rare, is a potentially serious side effect of SSRIs in which the levels of serotonin in your brain get too high. Serotonin syndrome is more likely to be triggered in people who are taking multiple medications or supplements such as St. John’s wort. Let your prescribing physician know If you are taking other medications or supplements alongside SSRIs. They can help you take steps to reduce your risk of serotonin syndrome.  

What are SNRIs?

SNRIs (AKA serotonin and norepinephrine reuptake inhibitors) are a type of antidepressant that work by increasing levels of two important neurotransmitters or chemicals in the brain: serotonin and norepinephrine.  

Some examples of SNRIs include:  

  • Duloxetine (Cymbalta)
  • Venlafaxine (Effexor, Effexor XR)
  • Levomilnacipran (Fetzima)
  • Desvenlafaxine (Pristiq, Khedezla)

How do SNRIs work?  

Similar to how SSRIs work by preventing serotonin from being mopped up by nerve cells after signaling, SNRIs prevent both serotonin and norepinephrine from being removed from circulation. The effects? More serotonin and norepinephrine are available to the brain.  

Norepinephrine, also called noradrenaline, is a hormone best known for giving you a rush of excitement when you’re watching a scary movie or skydiving. But noradrenaline isn’t just released in the face of perceived danger (like adrenaline is). It’s being released throughout the day to help you stay more alert. Say you’re studying for a big exam or getting off the couch to go to the gym—noradrenaline is working behind the scenes to help get you going.  

For people with depression, an increase in noradrenaline or norepinephrine levels in the brain are linked to a reduction in depressive symptoms.  

Conditions SNRIs can treat  

SNRIs are a type of antidepressant but can also be used to treat a wide range of mental and physical health conditions including:  

What are the side effects of SNRIs?  

Like SSRIs and other medications, SNRIs come with the possibility of side effects. The goal of medication is to help you feel better, not worse, and your prescribing physician will work with you to help reduce your risk of side effects. If you do experience any unpleasant side effects, be sure to bring them up with your doctor.  

The most common potential side effects of SNRIs include:

  • Nausea
  • Dizziness
  • Headaches
  • Dry mouth
  • Excessive sweating

Some less common side effects include:  

  • Suicidal ideation
  • Worsening depression  
  • Mania or hypomania
  • Tiredness
  • Constipation
  • Insomnia
  • Sexual dysfunction; reduced libido or other changes in sexual function or desire, including erectile dysfunction
  • Loss of appetite

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What is the difference between SSRIs and SNRIs?

The main difference between SSRIs and SNRIs is that SSRIs work by increasing levels of just one type of neurotransmitter (serotonin) whereas SNRIs increase levels of two types of brain chemicals, noradrenaline and serotonin.  

Both medications come with the possibility of side effects, though these are typically mild and short-term.  

A licensed physician, like a psychiatrist, can provide guidance around which antidepressant, if any, might be right for you.  

Are SSRIs or SNRIs more effective?

Although SSRIs are more commonly prescribed than SNRIs, one type of medication is not more effective than the other. Mental health conditions are complex and treatment is not one-size-fits-all. A medication that works well for one person, may not be the right one for you.  

A licensed prescriber will be able to work with you on a personalized treatment plan that is dependent on your needs, symptoms, and response to medications.  

Can SSRIs and SNRIs help with anxiety?

SSRIs and SNRIs are both used to treat anxiety disorders such as generalized anxiety disorder, OCD, and PTSD, though they won’t work for everyone. Many people with an anxiety disorder also experience symptoms of depression and SSRIs and SNRIs can be effective for relieving both sets of symptoms.  

If your doctor has recommended medication as part of your treatment plan, you may be concerned about becoming ‘dependent’ on the medication in order to function. Unlike certain types of antianxiety medications like benzodiazepines, antidepressants don’t create a dependency or addiction and can be safely discontinued over time under the supervision of your licensed prescriber.

Like treatment for depression and other mental health conditions, treatment for anxiety is highly personalized, so chat with your doctor to see which treatment options might be best for you.  

The bottom line

If you’re experiencing depression or another mental health disorder, you’re likely eager to get your symptoms under control so you can get back to living your life. The first step to feeling better is to schedule an appointment with your doctor.  

A primary care provider or psychiatrist is a good place to start. Your doctor will be able to evaluate your needs and symptoms and create a personalized treatment plan that’s right for you. This may include medication, like SSRIs or SNRIs, talk therapy, or both.  

SSRIs and SNRIs are two types of antidepressants that can be effective for reducing symptoms of depression. They wok by increasing levels of certain chemicals in your brain that regulate mood and energy. Both medications come with side effects, and one isn’t necessarily more effective or better than the other. Your doctor will be able to discuss the pros and cons of starting a medication like an SSRI and SNRI and help you determine which might be right for you.  

Medications can be extremely helpful for people experiencing mental health conditions and there’s no shame in needing them in order to get better.  


Side effects - Selective serotonin reuptake inhibitors (SSRIs) | NHS

What is Noradrenaline | Mental Health America

Selective Serotonin Reuptake Inhibitors | StatPearls  

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Dr. Glenn Occhiogrosso is board-certified in Adult Psychiatry and Addiction Psychiatry. He has been practicing in New York City for over ten years and is a lifelong New Yorker.

Dr. Occhiogrosso earned his medical degree from SUNY Downstate Health Sciences University in Brooklyn. He then completed his residency and an Addiction Fellowship at Mount Sinai Beth Israel in Manhattan.

After completing his fellowship, Dr. Occhiogrosso returned to Brooklyn to be Unit Chief for the inpatient Detoxification Service at Kings County Hospital Center. During his ten years at Kings County, Dr. Occhiogrosso served as the Psychiatry Clerkship Director for St. George’s University School of Medicine, Associate Program Director for the SUNY Downstate Residency Program, Medical Director of the Adult Inpatient Psychiatric Service, and Clinical Director of the Comprehensive Psychiatric Evaluation Program (CPEP). While working in these distinctly different areas, Dr. Occhiogrosso gained valuable experience treating a wide range of clinical presentations and pathologies. As a result, he is comfortable treating patients across the entire spectrum of mental and behavioral health conditions.

Dr. Occhiogrosso’s practice focuses on medication management, but his patients will also benefit from supportive therapy and motivational interviewing techniques. In some instances, where the addition of more in-depth therapy would better optimize treatment, Dr. Occhiogrosso will recommend potential therapists and collaborate actively with them to provide comprehensive care.

Dr. Occhiogrosso has held faculty appointments at SUNY Downstate Medical Center and St. George’s University School of Medicine. In addition, Dr. Occhiogrosso spent nearly all of his professional career teaching, mentoring, and supervising psychiatric residents and medical students alongside his clinical work.

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