Introduction
If you’re seeking or receiving treatment for depression or anxiety, it’s likely you’ve come across medications known as SSRIs and SNRIs. These are the most common types of antidepressants, and they’re considered first-line treatments for many mental health conditions.
These two medications function in very similar ways, but they are not exactly the same. Understanding the key differences between them will let you know what to expect when starting these medications, and could provide some insight into which choice might be best for you.
Let’s take a look at how they work, how they differ, and what you need to know.
What are SSRIs?
Selective serotonin reuptake inhibitors, also known as SSRIs, are the most commonly prescribed class of antidepressants. They treat symptoms of depression by increasing the levels of serotonin in the brain.
Examples of SSRI medications include:
- Fluoxetine (Prozac)
- Sertraline (Zoloft)
- Escitalopram (Lexapro)
- Paroxetine (Paxil)
- Citalopram (Celexa)
How do SSRIs work?
Serotonin is a neurotransmitter in your brain that helps to regulate your mood. It acts as a chemical messenger between your nerve cells and contributes to key functions within your body. Normally, once the serotonin has done its job of sending a signal to your nervous system, the chemical is reabsorbed by your cells and removed from circulation. But a “reuptake inhibitor” prevents some of that absorption, thus leaving more serotonin left for your brain to use. And having higher levels of serotonin in your brain results in a more stable mood and more positive emotions.
What is serotonin?
Serotonin is a neurotransmitter in your brain that is sometimes referred to as the “feel-good chemical”. Neurotransmitters are used by your nervous system to send messages to other neurons. Serotonin impacts human behavior, and plays a role in the state of your body and of your mood.
Some key effects of serotonin include: regulating your sleep cycle; influencing your appetite; and impacting your learning, memory, and executive function. Serotonin also allows you to control your mood and react appropriately to external situations.
Low levels of serotonin are linked to: difficulty processing stimuli; getting frustrated more quickly than you should; easily depleted energy levels; and difficulty finding pleasure in normally enjoyable activities. Because the amount of the chemical in your brain seems to impact the ability to control your mood, many mental health medications focus on increasing the levels of serotonin.
What conditions do SSRIs treat?
Although SSRIs are antidepressants, they are commonly used to treat a wide range of mental 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
SSRIs are considered first-line treatments when it comes to anxiety and depression; meaning prescribers tend to start with this type of medication before moving on to alternate treatments.
What are the side effects of SSRIs?
Common side effects of SSRIs may include:
- Feeling agitated, shaky, or anxious
- Gastrointestinal issues
- Weight changes
- Sexual dysfunction/reduced libido
- Dizziness
- Blurred vision
- Dry mouth
- Excessive sweating
- Insomnia
- Drowsiness
- Headaches
These side effects usually subside over time, but speak to your doctor if any persist.
Rare side effects of SSRIs include:
- Bruising or bleeding easily
- Difficulty urinating
- Hallucinations
- Confusion
- Movement problems
If you experience these side effects, seek medical attention immediately.
What are SNRIs?
Serotonin and norepinephrine reuptake inhibitors (SNRIs) are another common type of antidepressant. Like SSRIs, they increase the levels of serotonin in the brain; but they also increase the levels of another chemical called norepinephrine.
Examples of SNRIs include:
- Venlafaxine (Effexor)
- Duloxetine (Cymbalta)
- Desvenlafaxine (Pristiq)
- Levomilnacipran (Fetzima)
How do SNRIs work?
SNRIs are reuptake inhibitors, just like SSRIs. They prevent the reuptake of two neurotransmitters: serotonin and norepinephrine. That means that instead of getting reabsorbed by your nerve cells after sending their signals, the chemicals remain available for the brain to utilize. Higher levels of serotonin leads to a more positive mood; and an increased amount of norepinephrine helps the brain stay alert and motivated. Increased levels of both chemicals are linked to a reduction in depression and anxiety symptoms.
What is norepinephrine?
Norepinephrine, sometimes known as noradrenaline, is another neurotransmitter in the brain. It works with your adrenaline to help you stay alert and motivated.
Norepinephrine is responsible for: giving you more energy; waking you up and getting you moving; and helping you pay attention and stay focused.
Low levels of norepinephrine result in: depression and lack of motivation; a lack of energy; and poor memory and concentration. Therefore, targeting the levels of norepinephrine in the brain can be helpful in treating anxiety, depression, and ADHD.
What conditions do SNRIs treat?
SNRIs are a type of antidepressant, and their primary use is in treating conditions related to depression. They are also commonly prescribed to treat anxiety. In addition, SNRIs are often used to treat chronic nerve pain. Conditions treated by SNRIs include:
- Major depression
- Generalized anxiety disorder
- Panic disorder
- Social phobia
- Diabetic peripheral neuropathy
- Fibromyalgia
- Musculoskeletal pain
- Osteoarthritis
What are the side effects of SNRIs?
SNRIs can potentially cause all of the same side effects as SSRIs.
They also may include:
- Constipation
- Nausea
- Loss of appetite
- Panic attacks
- Physical weakness
Side effects may vary widely even among medications of the same class. If you are experiencing persistent side effects, speak to your doctor. They may recommend switching you to another medication. Just because one SNRI doesn’t work for you doesn’t mean another won’t; and how the body responds to each medication depends entirely on the individual.
What’s the difference between SSRIs and SNRIs?
SSRIs and SNRIs are very similar drugs, because they are both reuptake inhibitors that impact neurotransmitters in the brain. Neurotransmitters carry chemical messages from one neuron to the next. After the signal has been sent, the neurotransmitter is usually then reabsorbed by the nervous system. A reuptake inhibitor stops or reduces that reabsorption from happening, leaving more of the chemicals available for the brain to use.
SSRIs inhibit the reabsorption of one chemical, while SNRIs impact two. Both types of antidepressants prevent the reuptake of serotonin. SNRIs also prevent the reuptake of the chemical norepinephrine, in addition to serotonin.
Which is better, SSRIs or SNRIs?
SSRIs are more commonly prescribed than SNRIs, but that doesn’t mean that they are definitively more effective. Every individual has their own unique set of symptoms and mental health challenges; and the impact of each medication can be just as varied from person to person.
Both SSRIs and SNRIs are considered effective treatments for mental health conditions. It can be several weeks before they take full effect. Either drug can have mild side effects, most of which should improve over time. These antidepressants may interact with other medications or over-the-counter supplements, so be sure to inform your provider of everything you’re currently taking before starting an SSRI or SNRI.
Your doctor will review your medical history and current symptoms, and prescribe a medication they think will be best for you. It’s important that you try to track both symptom improvement and any side effects, and to speak to your doctor throughout the process. Just because one medication doesn’t work for you does not mean another medication won’t, and some people have to try more than one at first. Your provider will work with you over time to find the medication, or combination of medications, that is the most effective at treating your symptoms without severe side effects.
Can SSRIs or SNRIs treat anxiety?
Both SSRIs and SNRIs are often prescribed to treat anxiety, including Generalized Anxiety Disorder. Many people experience a significant improvement in anxiety symptoms after taking these medications.
Antidepressants are a safe and non-addictive treatment option for anxiety. Though not all medications will work for everyone, they are considered a first-line treatment for anxiety in addition to depression.
Final thoughts
SSRIs and SNRIs are two similar but different classes of antidepressants, and are the most commonly prescribed medication types for treating depression and anxiety. They both function by increasing the levels of chemicals that impact mood, emotions, and motivation. SSRIs are slightly more common than SNRIs, but both are effective for many people in treating their symptoms.
The only way to know which medication is right for you is to discuss with a qualified healthcare provider. They will go over your medical history, current symptoms, and previous medications to determine what’s best for you. Don’t be discouraged if a medication doesn’t work at first - ongoing care is key, and your doctor will discuss your options and work with you to eventually find the right treatment.
Sources
What Is Serotonin? | Mental Health America
Overview - SSRI antidepressants - NHS
Side effects - Selective serotonin reuptake inhibitors (SSRIs) - NHS
What is Noradrenaline? | Mental Health America
Serotonin Norepinephrine Reuptake Inhibitors: A Pharmacological Comparison - PMC
Side effects - Antidepressants - NHS
