Skip to content

Serotonin and norepinephrine reuptake inhibitors


Serotonin and norepinephrine reuptake inhibitors


0 / 8 complete

Serotonin and norepinephrine reuptake inhibitors

8 flashcards
External References

Content Reviewers:

Yifan Xiao, MD

Serotonin norepinephrine reuptake inhibitors, or SNRIs, are mainly used to treat major depressive disorder.

This disorder causes a persistent feeling of sadness and loss of interest in everyday activities.

Even though the exact cause of depression is still unknown, there's some evidence that suggests it’s related to low levels of neurotransmitters like serotonin, norepinephrine, and dopamine.

Serotonin norepinephrine reuptake inhibitors work by increasing the levels of serotonin and norepinephrine to alleviate the symptoms of depression.

Alright, now within the brain, there are many different types of neurons, but we’re going to focus only on two: serotonergic neurons which produce serotonin, and noradrenergic neurons which produces norepinephrine.

Each of these neurons synthesizes and stores their neurotransmitters in small vesicles.

So, when an action potential reaches the presynaptic membrane, these vesicles fuse with the membrane, releasing neurotransmitters in the synaptic cleft.

Once released, serotonin or 5-HT binds to 5-HT2 receptors on the postsynaptic membrane, thereby increasing neural stimulation and regulating mood, feeding, and reproductive behavior.

On the other hand, norepinephrine binds to norepinephrine receptors on the postsynaptic membrane, boosting alertness.

As long as there’s a high enough concentration of neurotransmitters in the synaptic cleft, the postsynaptic neurons will continue to fire.

Now, serotonergic neurons on their presynaptic membrane have serotonin transporters or SERT, while noradrenergic neurons have norepinephrine transporters or NET.

These membrane proteins transport the serotonin and norepinephrine in the synaptic cleft back into presynaptic neurons.

This leads to decreased neurotransmitter concentration within the synaptic cleft, causing the postsynaptic neurons to stop firing.

So, in conditions such as major depressive disorder, where there are low levels of serotonin and norepinephrine, SNRIs can be used.

Common medications in this class include duloxetine, venlafaxine, and desvenlafaxine, which is actually an active metabolite of venlafaxine, milnacipran, and levomilnacipran.

SNRIs bind to serotonin and norepinephrine transporters and inhibit them, leading to increased levels of these neurotransmitters within their synaptic clefts.

Other conditions that can be treated with SNRIs include anxiety and neuropathic pain like peripheral neuropathy.

For medication specific indications, duloxetine can be used to treat urinary incontinence, which is an uncontrollable leakage of urine; and fibromyalgia, which is a condition characterized by chronic muscle pain, fatigue, and sleep problems.

On the other hand, venlafaxine is indicated in social anxiety, panic disorders, post-traumatic stress disorder or PTSD and obsessive-compulsive disorder or OCD.

Lastly, venlafaxine can treat postmenopausal hot flashes, which are sudden feelings of heat, usually most intense over the face, neck, and chest.

Side effects of SNRIs include insomnia, nausea and sexual dysfunctions.

Also, due to increased levels of norepinephrine, SNRIs can cause high blood pressure, sweating, and headaches.

The most dangerous, however, are suicidal ideations, especially in individuals under 25, and serotonin syndrome, which is a life-threatening condition caused by serotonin accumulation and over stimulation of the nervous system.

This syndrome is characterized by skin flushing, hyperthermia, agitation, muscle rigidity, seizure, and coma.

It usually occurs in individuals treated with a combination of SNRIs and other antidepressants that increase serotonin level, such as monoamine oxidase inhibitors.


Serotonin and norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant medications used to treat major depressive disorder and other mental health conditions such as anxiety disorders, obsessive-compulsive disorder, and attention deficit hyperactivity disorder. SNRIs work by preventing serotonin and norepinephrine reuptake from the synaptic cleft, thus enhancing the effect of both neurotransmitters on the postsynaptic neuron. SNRIs can cause a few dangerous side effects like increased risk of suicide and life-threatening serotonin syndrome.

  1. "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
  2. "Rang and Dale's Pharmacology" Elsevier (2019)
  3. "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
  4. "Mechanism of action of antidepressant medications" J Clin Psychiatry (1999)
  5. "Addressing the Side Effects of Contemporary Antidepressant Drugs: A Comprehensive Review" Chonnam Medical Journal (2018)
  6. "Neuroleptic malignant syndrome and serotonin syndrome" Thermoregulation: From Basic Neuroscience to Clinical Neurology, Part II (2018)
  7. "Do SSRIs and SNRIs reduce the frequency and/or severity of hot flashes in menopausal women" J Okla State Med Assoc (2017)