Serotonin-norepinephrine reuptake inhibitors (SNRIs)

Serotonin-norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant drugs used to manage depression symptoms and treat several other mental health and pain-related conditions. They are widely prescribed in psychiatry and primary care and are approved by the U.S. Food and Drug Administration for multiple indications. SNRIs affect key neurotransmitters in the brain that influence mood, pain perception, and stress responses. Compared with older classes of antidepressants, SNRIs are generally well tolerated and are often chosen when symptoms involve both emotional and physical components, such as chronic pain or fatigue.

SNRIs are a type of antidepressant that increase the levels of serotonin and norepinephrine, also known as noradrenaline. These neurotransmitters help brain cells communicate and play a major role in regulating mood, focus, energy, and pain signals within the central nervous system (CNS). SNRIs are a class of antidepressants that work differently from selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants(TCAs), and monoamine oxidase inhibitors (MAOIs).

SNRIs are often prescribed when SSRIs do not fully relieve symptoms or when a person also experiences chronic pain, neuropathy, or musculoskeletal pain alongside depression.

To understand how SNRIs work, it helps to look at basic neuroscience. Neurons send messages using neurotransmitters. After a signal is sent, these chemicals are usually taken back up into the neuron. SNRIs work by blocking this reuptake process for serotonin and norepinephrine. This inhibition increases the amount of these neurotransmitters available between neurons, which can improve communication in brain pathways involved in mood and pain regulation.

SNRIs’ pharmacology involves acting on both serotonin and noradrenaline; this differs from SSRIs, which mainly affect serotonin alone. This dual action is why SNRIs may be helpful for people with major depressive disorder, generalized anxiety disorder, panic disorder, and certain pain conditions. Although dopamine is not a primary target, changes in serotonin and norepinephrine signaling can indirectly influence dopamine pathways related to motivation and focus.

Several SNRIs are currently FDA-approved and commonly prescribed:

• Venlafaxine (Effexor)
• Venlafaxine extended-release (Effexor XR)
• Desvenlafaxine (Pristiq and Khedezla)
• Duloxetine (Cymbalta)
• Levomilnacipran (Fetzima)
• Milnacipran (Savella)

These medications differ in dosing, side effect profiles, and approved uses. Extended-release versions are designed to improve tolerability and reduce withdrawal symptoms if a dose is missed.

SNRIs are approved for the treatment of depression, including major depressive disorder. They are also commonly used for several anxiety disorders, such as generalized anxiety disorder and panic disorder. Beyond mental health, SNRIs play an important role in managing chronic pain conditions.

Duloxetine and milnacipran are approved for fibromyalgia and musculoskeletal pain. Duloxetine is also used for diabetic neuropathy and osteoarthritis-related pain.

In some cases, SNRIs may be prescribed off-label for conditions not specifically listed on the label, based on clinical trials, meta-analysis data, or systematic review findings that support their effectiveness.

SNRIs can cause side effects, especially when starting treatment or adjusting the dose. Many side effects improve over time as the body adapts, but some may persist.

Common side effects of SNRIs include:

• Nausea
• Dry mouth
• Constipation
• Dizziness or lightheadedness
• Sweating more than usual
• Headache

-Drowsiness or fatigue

• Trouble sleeping
• Decreased appetite or weight loss
• Sexual dysfunction

Other possible side effects include:

• Increased blood pressure
• Faster heart rate
• Anxiety or restlessness
• Shakiness
• Blurred vision

Less common but more serious side effects may include:

• Serotonin syndrome, especially when combined with other serotonergic medications
• Worsening depression or suicidal thoughts, particularly in young adults
• Withdrawal symptoms if the medication is stopped suddenly, also called discontinuation syndrome

These are not all of the possible side effects of serotonin-norepinephrine reuptake inhibitors (SNRIs). You should always seek medical advice from your healthcare provider for any questions or concerns about your medical condition or treatment. Read all patient information, medication guides, or drug information sheets that come with this medication. You can also report adverse effects to the Food and Drug Administration at www.fda.gov/medwatch or 1-800-FDA-1088.

Although these medications are generally well-tolerated and safe, there are certain warnings, precautions, and drug interactions you should be aware of.

Warnings

Before starting serotonin-norepinephrine reuptake inhibitors (SNRIs), it is crucial to discuss any existing health conditions with your healthcare provider, including if you have:

• A history of suicidal thoughts or suicide attempts
• Bipolar disorder or a history of manic episodes
• High blood pressure or heart disease
• Glaucoma, particularly angle-closure glaucoma
• Seizure disorders or a history of seizures
• Liver disease
• Kidney disease
• Bleeding problems
• A history of serotonin syndrome
• Alcohol use disorder
• Pregnancy or plans to become pregnant
• Breastfeeding or plans to breastfeed

Boxed Warning

SNRIs carry a boxed warning regarding an increased risk of suicidal thoughts and behaviors in children, adolescents, and young adults, particularly during early treatment. Careful monitoring by healthcare professionals and caregivers is essential.

Contraindications

SNRIs should not be used with monoamine oxidase inhibitors (MAOIs), due to the risk of serotonin syndrome and other serious effects. A washout period is required when switching between these classes. People with uncontrolled high blood pressure or certain heart conditions may also need alternative treatment options.

Drug interactions

When serotonin-norepinephrine reuptake inhibitors (SNRIs) are taken with other prescription drugs, over-the-counter medications, vitamins, and supplements, it may change how they work or increase the frequency or severity of side effects. Make sure that you tell your healthcare professional about anything that you are taking to avoid any negative drug interactions, including:

• MAOIs (monoamine oxidase inhibitors)
• Other antidepressants, including SSRIs, tricyclic antidepressants, and other SNRIs
• St. John’s wort
• Triptans used for migraines
• Certain pain medications, including tramadol and some opioids
• Blood thinners such as warfarin and antiplatelet medications
• Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen
• Stimulants
• Alcohol
• Certain antibiotics and antifungal medications