How Do SSRIs Work? The Mechanism Behind Zoloft, Lexapro, and More
Key takeaways:
Selective serotonin reuptake inhibitors (SSRIs) like sertraline (Zoloft) and escitalopram (Lexapro) are a group of medications that treat depression, anxiety, and other mental health conditions.
SSRIs work by raising the level of a chemical — called serotonin — in the brain. They may also help the brain process serotonin more effectively. And they may affect other brain chemicals as well, but to a lesser degree.
If your SSRI doesn’t seem to improve your symptoms within 4 to 6 weeks of starting it, talk to your healthcare provider. They may increase your dose or recommend another medication.
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Table of contents
Selective serotonin reuptake inhibitors (SSRIs) are a first-choice treatment option for mental health conditions such as major depressive disorder (MDD) and generalized anxiety disorder (GAD). They’re considered effective and safe for many people. But it generally takes a few weeks to feel their effects.
Here, we’ll dive a little deeper into exactly what an SSRI is. We’ll also cover how SSRIs work to address symptoms of depression, anxiety, and more.
What is an SSRI?
SSRIs are part of a broad group of medications called antidepressants. They’re commonly known for treating depression and anxiety. But SSRIs are also sometimes used in other health conditions. Examples include:
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What are some common SSRIs?
Several SSRIs are FDA approved to treat one or more of the health conditions mentioned above. Examples include:
Citalopram (Celexa)
Escitalopram (Lexapro)
Fluoxetine (Prozac)
Fluvoxamine (Luvox)
Paroxetine (Paxil)
Sertraline (Zoloft)
How do SSRIs work?
The brain has chemical messengers that help nerve cells in your brain (neurons) communicate with each other. These messengers are known as neurotransmitters, and they play a major role in regulating how our brain works. They’re involved in everyday actions we don’t often think about, like breathing. They’re also involved in managing how we feel and our ability to learn.
SSRIs are thought to work mainly by raising levels of a certain neurotransmitter, called serotonin, in the brain. Usually, after serotonin helps transport a message from one nerve to another, it gets picked back up (reabsorbed) by the first nerve. SSRIs prevent serotonin from being reabsorbed by nerve cells after carrying its message. This makes more serotonin available for your brain to use.
SSRIs are “selective,” meaning they mostly affect serotonin. Some SSRIs also affect other neurotransmitters, but not as much as serotonin.
Do SSRIs do anything besides increase serotonin?
Though many different factors may lead to anxiety and depression, low serotonin levels are often seen in people with these mental health conditions. By raising serotonin levels, SSRIs can help relieve the symptoms of depression and anxiety for some people. SSRIs might also help your brain use serotonin more efficiently.
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But SSRIs may have other ways of alleviating depression, too. In recent years, scientists have looked into a certain protein in the brain called brain-derived neurotrophic factor (BDNF). The amount of BDNF you have in your brain is important. It helps regulate how brain neurons work. It's involved in learning, memory, and mood regulation.
Research has shown that antidepressants like SSRIs make BDNF more active, which may help improve depression symptoms as a result.
How long does it take for SSRIs to work?
In general, it can take 1 to 2 months for SSRIs to take full effect. But some symptoms may start to improve in 2 weeks or less.
For example, some people experience improvement in negative affective bias within a couple weeks of starting an SSRI. This is the tendency to pay more attention to negative thoughts than positive thoughts. Anxiety is another symptom that may improve within a couple weeks.
So, why do antidepressants take a couple weeks or more to work? The reason isn’t completely understood. But it may just take a while for our brain to respond to an SSRI, even though serotonin levels increase almost immediately.
After starting an SSRI, check in with your healthcare provider to update them on how you feel. If you aren’t feeling any improvements in your mood after 4 to 6 weeks, your healthcare provider may recommend a higher dose or a different medication.
What are the side effects of SSRIs?
SSRIs share some common side effects. But some SSRIs may be more likely to cause certain side effects than others. The good news is if you aren’t able to tolerate the side effects of one SSRI, you might be able to use a different one.
Common side effects
SSRIs are considered safe for most people. Still, more common side effects include:
Nausea, vomiting, or diarrhea
Headache
Dry mouth
Sexual problems, such as erectile dysfunction
Sleep problems
Anxiety
Weight loss or weight gain
Keep in mind that these side effects may be more or less likely depending on which SSRI you take. For example, stomach problems are more likely with fluoxetine and sertraline. But fluoxetine is the least likely to cause weight gain.
Serious side effects
Rare but serious side effects can happen when taking SSRIs. If you experience any of the following health issues, get medical help immediately.
1. Suicidal thoughts and behaviors
All SSRIs include a boxed warning about the risk of suicidal thoughts. A boxed warning is the strictest warning that the FDA assigns to a prescription medication. The risk is higher among people who are younger than 25 years old. It’s also more common in the first few months of SSRI treatment, or after you change your dose.
If you or someone you know is having thoughts of suicide, you’re not alone, and help is available. Call the National Suicide Prevention Lifeline at 988, or text HOME to 741-741 to reach the Crisis Text Line.
2. Serotonin syndrome
Serotonin syndrome is a condition of too much serotonin in your body. The risk is higher when you take an SSRI with other medications that also raise serotonin. Serious symptoms of serotonin syndrome include fast heart rate, confusion, and uncontrollable body movements.
3. Abnormal heart rhythm (arrhythmia)
SSRIs can increase your risk of abnormal heart rhythms (arrhythmias). Citalopram may have a higher risk of this than other SSRIs. Combining SSRIs with other medications that have the potential to cause arrhythmias can put you at greater risk.
4. Bleeding
Medications that increase serotonin levels can raise the risk of bleeding. This is more common if you’re also taking other medications that can cause bleeding, such as nonsteroidal anti-inflammatory drugs (NSAIDs). These include common over-the-counter medications like ibuprofen (Advil, Motrin), naproxen (Aleve), and aspirin.
The bottom line
SSRIs are prescription medications that treat depression, anxiety, and other mental health conditions. Levels of the chemical serotonin may be low or underactive in these mental health conditions. SSRIs are thought to work by raising levels of serotonin and possibly other chemicals.
SSRIs may help improve symptoms of depression and anxiety within 2 weeks, but in many cases they can take 1 to 2 months to have a significant effect. If it doesn’t feel like your SSRI is improving your symptoms within 4 to 6 weeks of taking it, talk to your healthcare provider. They may try another medication or increase your dose.
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References
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