How do SSRIs work?

Samir Kadri
Author: Samir Kadri Medical Reviewer: Morgan Blair Last updated:

Selective serotonin reuptake inhibitors (SSRIs) are the most prescribed antidepressants across the nation. [1]

They are the front-line medication for depression and many other mental health disorders due to their safety and effectiveness. [1] They are FDA-approved for the treatment of adults and children. [1]

What do SSRIs do to the brain?

The function of SSRIs is to regulate and increase the amount of serotonin in the brain. Serotonin is a neurotransmitter that is widely considered to influence a person’s emotions, memory, sleep quality, and general mood. [2] It’s often referred to as the “feel-good” neurotransmitter because it contributes to feelings of well-being and happiness.

Neurotransmitters are brain messenger chemicals that transfer signals between nerve cells in the brain, also known as neurons. [2] Neurons in the brain release serotonin into the synapse, which is the small space between two neurons. After the neurotransmitter has transmitted its signal, it needs to be cleared from the synapse so that the signal doesn’t continuously fire.

Cells in the brain have proteins on their surfaces called transporters, which are responsible for reabsorbing neurotransmitters like serotonin from the synapse back into the neuron that released them. This process is known as reuptake. [2]

SSRIs work by inhibiting the reuptake of serotonin. They bind to and block the serotonin transporters on the neuron’s surface. By doing so, they slow down the reabsorption of serotonin into the neuron, allowing more serotonin to remain in the synapse for a longer duration. [2]

This means there is an increased concentration of serotonin available to bind to receptors on neighboring neurons. This increases the transmission of serotonin across the brain, which is thought to lead to improvements in mood and emotional regulation.

The relative safety and comfort SSRIs provide to patients makes them a popular choice of antidepressant. SSRIs have little to no impact on the activity of other neurotransmitters, such as dopamine or norepinephrine. [1] As a result, SSRIs have fewer side effects than other antidepressants, such as tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs).

FDA-Approved SSRIs

The current SSRIs that are FDA-approved in the United States are: [1]

SSRIs are currently FDA-approved to treat the following conditions: [1]

How are SSRIs administered?

SSRIs are only available for oral consumption and come in multiple forms including capsules, tablets, or liquid solutions. [1] They are absorbed by the digestive system into the bloodstream.

The specific instructions for administration can vary depending on the type of SSRI, the condition being treated, and the healthcare provider’s recommendations. You ought to take any antidepressant exactly as prescribed by your healthcare provider.

SSRIs are typically taken once per day in the morning or the evening. With the exception of vilazodone, SSRIs may be taken irrespective of whether you have eaten. Vilazodone should be administered alongside food. [1] That said, it’s important to follow the specific instructions provided by the prescribing healthcare professional or the medication’s label.

How long until SSRIs start working?

The time it takes for SSRIs to become effective can vary from person to person and depends on several factors, including the specific SSRI being used, the condition being treated, individual response, and the severity of the symptoms.

It may take about 2 to 4 weeks of consistent SSRI use before you observe a reduction in symptoms. As you continue taking SSRIs, their effect on treating symptoms ought to be more noticeable. During this period, schedule regular check-ins with your doctor to determine how effectively your SSRIs are treating your symptoms.

  1. Chu A, Wadhwa R. Selective Serotonin Reuptake Inhibitors. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:
  2. How SSRIs work | OCD-UK. (n.d.).
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Samir Kadri
Author Samir Kadri Writer

Samir Kadri is a medical writer with a non-profit sector background, committed to raising awareness about mental health.

Published: Oct 18th 2023, Last edited: Jan 31st 2024

Morgan Blair
Medical Reviewer Morgan Blair MA, LPCC

Morgan Blair is a licensed therapist, writer and medical reviewer, holding a master’s degree in clinical mental health counseling from Northwestern University.

Content reviewed by a medical professional. Last reviewed: Oct 18th 2023