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Selective serotonin reuptake inhibitors are the most prescribed antidepressant medication. There are a variety of SSRIs out there that are all slightly different. In this lesson you will review what SSRIs are and how they work.

What are SSRIs?

Selective serotonin reuptake inhibitors are known for helping with depression. Of all of the antidepressant medications, SSRIs are the most commonly prescribed medication to help with depression and other anxiety based disorders such as OCD. They work with the body’s natural chemistry to help communicate the correct messages to the brain.In order to make sense of what SSRIs are and how they work, there are a few terms you will need to be familiar with:

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  • Neurotransmitters are chemicals that send messages to the brain (Serotonin is the neurotransmitter that will be discussed in this lesson.


  • Receptors are spots on neurons/cells where the neurotransmitters go to send their messages. They are like little mailboxes that will only take specific mail/neurotransmitters.
  • Serotonin is a neurotransmitter that can be found throughout most of the body. It is believed to have a great affect on mood, appetite, sleep, memory, learning, sexual desire and function, temperature, and social behavior.

  • Neurons are brain cells with two ends, the axon and the dendrites. The neuron receives the messages through the neurotransmitters, processes them, and sends them on to the brain.

The above terms are all related through neurotransmission. Neurotransmission is the processes that sends and receives messages of all types to the brain.

For instance, if you touch a hot stove, a chain reaction will begin where nerve cells start to communicate with each other. These messages will go to the brain and be translated into ‘Oh, no. That is hot. Remove your hand.’The neurotransmission involved with SSRIs involves a special neurotransmitter (chemical messenger), serotonin. The messages serotonin carries helps to regulate learning, sleeping, mood, and more.

During neurotransmission serotonin is released into the synapses (space between neurons). Serotonin then goes to the receptors that read it and send its message to the brain. When serotonin is done doing its job, the reuptake receptors collect all of the serotonin back to be released later. The diagram below shows how neurotransmission works.

When neurotransmission does not work properly, the brain does not receive the correct messages.


Anxiety disorders are perfect examples of when neurotransmission is not working correctly.

In most cases the person who is experiencing symptoms of these disorders is having an issue with neurotransmission involving serotonin. This is a chemical communications issue. Imagine being on the phone with technical support and they are just not understanding the issue you are trying to explain. This would be a communications problem. Then you decided to use more than just a phone and you bring in a web cam to show them the problem.

Communication becomes easier and now you can fix the problem and move on. SSRIs are like the web cam in the above scenario. It helps to make the proper communication to the brain more clear.

How Do SSRIs Work?

Selective serotonin reuptake inhibitors explains how it works right in its name.

So, let’s break it down. SSRIs are selective because they only or mainly affect the neurotransmitter, serotonin. SSRIs actually block (Inhibit) the ability for the re-absorption (reuptake) of serotonin in the brain.That is the short version of what SSRIs do. Now, here is the longer version…Serotonin is released from one neuron into the synapse or space between the two neurons.

Serotonin then fits inside of the receptors that are on the outside of the second neuron. Once they are in the proper receptors, a signal goes through the cell so that the second neuron can send on the message to the next. The message eventually reaches the brain. These messages can be about sleep, mood, hunger, anger, or anything.People who are experiencing disorders such as depression, anxiety, OCD, or even anger issues seem to have a lack of serotonin or a glitch within the neurotransmission process. There are different reasons for this happens.

They could have low brain production of serotonin, a low number of receptor sites or shortage of tryptophan, which makes serotonin. SSRIs help to make up for this lack of serotonin by blocking the receptors on the first neuron that suck the serotonin back up before it can send all of its positive messages. This leaves serotonin floating around longer allowing for more of the messages to be read, thus allowing the person to feel better.


Common SSRIs that are prescribed are:

  • Citalopram (Celexa)
  • Escitalopram (Lexapro)
  • Fluoxetine (Prozac, Prozac Weekly, Sarafem)
  • Paroxetine (Paxil, Paxil CR, Pexeva)
  • Sertraline (Zoloft)
  • Fluoxetine combined with the atypical antipsychotic olanzapine (Symbyax)

Like all medication SSRIs do have side effects. They have the common side effects such as diarrhea, nausea, headaches, and dry mouth. They can also cause increase nervousness, weight gain, drowsiness, and insomnia.

All medication should be taken under a doctor’s supervision.

Learning Outcomes

When you are done, you should be able to:

  • Recall what SSRIs are
  • Summarize the process of neurotransmission
  • Describe how SSRIs work
  • List some of the common SSRI medications and their side effects

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