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What are SSRIs?

Vanessa de la Cruz, MD

October 27, 2022


Selective Serotonin Reuptake Inhibitors, or SSRIs, are a widely used type of medication primarily used to treat depression and anxiety. SSRIs are popular because they tend not to produce many serious side effects or dependency issues like other medications. Although they are so commonly used, it is still essential to know the specific properties of SSRIs to learn what they are doing to your body and mind. Keep reading for an overview all about SSRIs! 

What is Anxiety? 

Anxiety is a natural and healthy feeling. It derives from our innate human response to potential dangers. However, when the anxiety presents itself in response to stimuli that are not dangerous or threatening and becomes disruptive to your daily functioning, it can turn into an anxiety disorder:


  1. Generalized Anxiety Disorder (GAD): GAD is categorized by excessive and persistent worry and anxiety about non-threatening stimuli. The stimuli that cause anxiety in GAD sufferers would not emit that response in the average individual. People with GAD may experience extensive worry, rumination, and physical anxiety symptoms due to mundane stimuli. They also may experience these anxiety symptoms without cause, almost as if the feelings of anxiety came out of nowhere. 
  2. Social Anxiety Disorder: Social Anxiety Disorder symptoms are similar to GAD, except a non-threatening social situation triggers them. For example, someone with healthy anxiety may sweat or worry before a big presentation in front of a group. On the other hand, a person with Social Anxiety Disorder will experience these symptoms in mundane social situations. For example, they can experience heightened anxiety before chatting with a friend or calling a restaurant to order food. 
  3. Panic Disorder and Anxiety Attacks: Panic Disorder is characterized by persistent panic attacks. Panic attacks are sudden and extreme feelings of fear that cause physical anxiety symptoms like chest pain and rapid breathing. They can be triggered by anxiety-inducing stimuli or occur randomly. Anxiety attacks are often less severe than panic attacks and come on slower but can be equally as distressing.

What is Depression?

Depression, although relatively common, is a serious mental illness that negatively impacts how one feels, thinks, and acts regarding their experiences. Like many mental disorders, various types of depression have different causes. Here are the most common types of depression and how they can appear: 


  1. Situational Depression: This type of depression does not count as disordered depression or sadness. Situational depression refers to the melancholy mood all people get into after a distressing event. The depressed mood you feel in situational depression is in direct response to an event and typically subsides over time.
  2. Major Depressive Disorder (MDD): People who suffer from major depressive disorder feel persistent depressive moods most of the time. Common symptoms are losing interest in what once was exciting, feeling sluggish and unmotivated, and having trouble making decisions. People with MDD may also experience physical symptoms like weight loss/gain, lack of energy, and slowed body movements. 
  3. Seasonal Depression or Seasonal Affective Disorder (SAD): People with SAD feel the same symptoms of major depressive disorder, except only within particular seasons. For most people, symptoms of SAD flare up in the winter months, and this is explainable by the wealth of research finding a solid association between shorter days/lack of sunlight and depression. 
  4. Persistent Depressive Disorder: Previously called “dysthymia,” this disorder is classified as experiencing depression symptoms for two consecutive years. Although people with this disorder may have periods of major depression, their typical symptoms are usually less severe, although long-lasting. 
  5. Postpartum Depression: Postpartum depression is the depression a person may experience after childbirth. This is not to be confused with “baby blues,” which have similar symptoms to postpartum depression but only last for about a week after birth. Postpartum depression can start during pregnancy and last many months after giving birth. Symptoms like severe mood swings, feelings of hopelessness, difficulty bonding with the baby, and severe anxiety make this disorder extremely difficult to deal with while caring for a newborn. 

How do SSRIs work?

To put it plainly, SSRIs work by increasing the level of serotonin in the brain. Serotonin is a neurotransmitter that carries messages from your nerve cells to your brain and throughout the rest of your body, affecting how your body works. Serotonin positively affects your mood, emotions, ability to sleep, sex drive, and memory. When the brain produces a normal amount of serotonin, it helps regulate and reduce feelings of anxiety and depression. However, some individuals have a lower level of serotonin in their brains than is typical, which can cause mental health issues like anxiety and depression. Taking SSRIs helps increase your serotonin levels, making you more susceptible to emotion regulation techniques and therapy and improving an overall more positive mood [1]. 

Although SSRIs were created primarily for the treatment of depression, they have completely revolutionized the treatment of anxiety and have become a “first-line” medication for anxiety [2]. The emergence of SSRIs in 1974 de-popularized the use of benzodiazepines to treat anxiety disorders, as SSRIs have been considered safer and less addictive than other anxiety-treating medications [2]. This is why SSRIs, an antidepressant group of medications, are so commonly used to treat anxiety and depression. 


Definition and example of the different kinds of SSRIs

SSRIs for Anxiety and Depression 

There are a handful of types of SSRIs commonly prescribed to treat both anxiety and depression. Although all medications tend to work in the same way and have a similar chemical makeup, there are slight differences in each of them. The decision about which SSRI is best for you is best left up to your doctor’s expertise. The most popular SSRIs are: 

  • Citalopram (Celexa)
  • Paroxetine (Paxil)


SSRI Side Effects 

Although SSRIs are generally safe and low in side effects, they can sometimes cause significant side effects. Fortunately, most people who take SSRIs only experience mild side effects (if any), which tend to subside the longer they are on the medication [1]. For example, those new to SSRIs may encounter mild side effects, like nausea, during the first few weeks of starting the medication, which subsides over time. Typically, side effects begin to occur during the first two weeks of taking an SSRI and subside in a few weeks [11] when the body fully adjusts to the new medication.

Below are the most common side effects of SSRIs: 

Common/Mild Side Effects:

  • Agitation or shakiness
  • Increased anxiety 
  • Nausea
  • Loss of appetite and/or weight loss
  • Dizziness
  • Headaches 
  • Excessive sweating 
  • Dry mouth
  • Trouble sleeping (insomnia and/or drowsiness)
  • Loss of libido*
  • Erectile dysfunction*

*may persist longer than the first few weeks of starting SSRI

It is necessary to continue taking the prescribed SSRI regularly, even if mild side effects persist. This is because SSRI medications take several weeks for you to benefit from their impact and see a difference in your levels of anxiety and depression [2]. By that time, the benefits of the medication and the improvement of feelings of anxiety and depression should outweigh the negatives of mild side effect(s). 

Uncommon/Serious Side Effects: 

  • Bruising and/or bleeding easily (including vomiting blood or having blood in feces)
  • Hallucinations 
  • Suicidal thoughts or desire to self-harm (higher risk for people under the age of 25)
  • Inability to urinate 
  • Confusion*
  • Issues with mobility (muscle stiffness/twitching or extreme shakiness)*
  • Shivering*
  • High fever (over 100℉)*
  • Seizures*
  • Irregular heartbeat*
  • Loss of consciousness*

*associated with “Serotonin Syndrome.”

If you experience serious side effects, contact your doctor immediately. They are uncommon but can be a sign of Serotonin Syndrome, which occurs when the level of serotonin in your brain becomes dangerously high. If you experience symptoms associated with Serotonin Syndrome, stop taking the medication and contact your doctor or emergency help immediately. 

SSRI Withdrawal Symptoms

While SSRIs aren’t known to be highly addictive, stopping your treatment abruptly or missing a few doses in a row can create withdrawal-like symptoms. These withdrawal symptoms are better known as “Antidepressant Discontinuation Syndrome.” They are relatively common, occurring in 20% of patients who quit their SSRIs all at once after at least six weeks of continued usage. This is because most SSRIs (excluding Prozac) have a short half-life, meaning that missing just a dose or two will likely abruptly diminish the SSRI concentration in the bloodstream. This, in turn, makes it more likely for the individual to experience side effects comparable to withdrawal symptoms. 

The approximate half-life of the most common SSRI medications are:

  • Citalopram (Celexa): 36 hours
  • Fluoxetine (Prozac): 96 to 144 hours (4 to 6 days)
  • Escitalopram (Lexapro): 30 hours
  • Paroxetine (Paxil) : 24 hours
  • Sertraline (Zoloft): 22 to 36 hours

SSRIs can cause changes in the brain that affect serotonin receptors, creating a period of adjustment and withdrawal when medication is stopped abruptly. The brain will “down-regulate” the receptors, so there is a balance between serotonin and receptors, leaving a sudden decrease in serotonin and down-regulated receptors when treatment is stopped. You are likely to experience unpleasant side effects after this. 

Common SSRI withdrawal symptoms are often described as “flu-like” symptoms or feeling the sudden re-emergence of anxiety and depression. Although these symptoms may be distressing, they are typically not severe. Common symptoms include: 

  • Fatigue
  • Headaches
  • Catatonia
  • Lightheadedness or dizziness 
  • Nausea 
  • Depersonalization
  • Trouble concentrating
  • Chills
  • Vivid dreams
  • Suicidal thoughts*
  • Muscle pain*
  • Psychosis*

*more rare/concerning symptoms. If you experience these, contact a doctor or professional immediately. 

If you think that SSRIs may be helpful to you, reach out to your healthcare provider so you can work together to find the right medication for you!

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