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Dec 12, 2022

Mental Health


SSRI and SNRI (antidepressants)

Antidepressants come in two basic types: selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs). While SNRIs raise serotonin levels as well as norepinephrine, SSRIs only raise serotonin levels.

Learn about Types of Depression

Why are serotonin and norepinephrine important?

Neurotransmitters are chemicals in your brain that aid in the transmission of nerve signals between neurons, and both SSRIs and SNRIs act on them.


Your body uses the neurotransmitter, serotonin, to control your mood. You may become depressed if your serotonin levels are too high or too low.

Low serotonin levels can also lead to anxiety, depressive thoughts, suicidal thoughts, or compulsive behaviors. If your serotonin levels are too high, you may feel less physically and mentally active and/or excited, causing you to feel more relaxed and sleepy.


A crucial component of your “fight-or-flight” response is another neurotransmitter called norepinephrine. Norepinephrine naturally increases during periods of high stress, such as when you feel threatened.

Norepinephrine is also involved in controlling your mood, sleep, attention, and memory. Low norepinephrine levels can make it difficult to focus, cause attention deficit hyperactivity disorder (ADHD) symptoms, or cause depressive symptoms in certain people.

Euphoria may be caused by norepinephrine levels that are too high. However, they can also result in hyperactivity, increased blood pressure, and panic attacks.


Prozac (Fluoxetine) Zoloft (Sertraline)
  • Increase your brain’s serotonin levels, helping with symptoms of numerous mental health conditions
  • They can take several weeks (approximately 4 weeks) to work/see results
  • Taken daily
  • Used to treat depression, anxiety, PTSD, suicidal thoughts, fibromyalgia, and other types of chronic pain
  • SSRI are “selective", meaning they only impact the amount of serotonin in your brain
  • Can be used to treat other medical conditions, such as hot flashes, OCD, and premenstrual dysphoric disorder
  • Increase norepinephrine levels, helping you concentrate and decreases depression
  • Some SNRI medications may treat diabetic neuropathy
  • This drug class can also be used off-label to treat other conditions, such as sleep disorders

There is insufficient evidence that one drug class or the other is consistently better for everyone.

Learn about The first few weeks on antidepressants

SSRI medications

  • Citalopram (brand: Celexa) 20–40 mg daily
  • Escitalopram (Lexapro) 10 mg daily
  • Fluoxetine (Prozac, Sarafem) 10–60 mg daily, or 90 mg weekly
    Sarafem 20 mg daily may be used for premenstrual dysmorphic disorder (PMDD)
  • Paroxetine (Paxil, Paxil CR, Pexeva, Brisdelle) 10-60 mg daily
  • Sertraline (Zoloft) 50–200 mg daily
    May be used for premenstrual dysmorphic disorder (PMDD)
  • Fluvoxamine IR/ER 50–300 mg daily
    This medication is only approved for the treatment of OCD

Common side effects of SSRIs

  • Sexual dysfunctions (i.e. decreased sexual desire, ejaculation difficulties, erectile dysfunction)
  • Sleepiness
  • Insomnia
  • Nausea
  • Dry mouth
  • Weakness
  • Tremor
  • Dizziness
  • Headaches
    But SSRIs may help for migraines if taken continuously

SNRI medications

  • Venlafaxine (Effexor XR) 37.5–375 mg daily
    Approved for the treatment of depression, generalized anxiety disorder, panic disorder, and social anxiety disorder
  • Duloxetine (Cymbalta) 40–60 mg daily, or 20-30 mg BID (twice a day)
    Approved for the treatment of depression, peripheral neuropathy (pain), fibromyalgia, generalized anxiety disorder, chronic musculoskeletal pain
  • Desvenlafaxine (Pristiq, Khedezla) 50 mg daily
    Approved for the treatment of depression
  • Levomilnacipran (Fetzima) 40–120 mg daily
    Approved for the treatment of depression

Common side effects of SNRIs

  • Increase heart rate
  • Dilated pupils
    This can lead to an episode of narrow open-angle glaucoma
  • Dry mouth
  • Excessive sweating
  • Constipation
  • Dizziness
  • Nausea
  • Headaches

Speak With Your Doctor

Both SSRIs and SNRIs have been shown to significantly reduce symptom severity in many individuals with depression, anxiety, and various medical conditions.

Learn more about how SSRIs and SNRIs are used to treat depression and general anxiety disorder.

To get started on your treatment plan, talk to your healthcare provider about choosing between SSRI or an SNRI, and send your prescription to Marley Drug. Save up to 95% compared to your local pharmacy by using Marley Drug.

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Different Types of Depression