SSRIs

What Is Serotonin Syndrome? What You Need to Know If You Take SSRIs

Q: Can too much serotonin cause anxiety?

Yes, too much serotonin can absolutely cause anxiety . Researchers think serotonin might act on a nervous network in the brain that regulates mood and feelings of anxiety.

Written by Sameer Hassamal, MD | Reviewed by Frank Schwalbe, MD

Updated on February 26, 2026

FotografiaBasica/E+ via Getty Images

Key takeaways:

Serotonin syndrome is a rare, but potentially dangerous, reaction to medications that affect serotonin.
It can be caused by many common medications, including antidepressants, pain relievers, antibiotics, antihistamines, antinausea medications, migraine medications, and some herbal supplements.
It’s more likely to happen in people who take two or more of these medications at the same time.
Most people with serotonin syndrome have mild symptoms that resolve quickly. But, in some cases, serotonin syndrome can be a medical emergency.

Serotonin is a chemical that affects mood and how the brain responds to things like fear, anxiety, and stress. Many medications increase serotonin levels, including some commonly prescribed for nausea and pain.

Serotonin syndrome happens when serotonin levels are too high in your body. Many cases of serotonin syndrome are mild, but severe cases can be life-threatening. If you or a loved one takes medications that can cause serotonin syndrome, it can be helpful to know what to look out for.

What is serotonin syndrome?

Serotonin syndrome, also called serotonin toxicity, is a condition caused by medications that increase serotonin levels in your body. It happens when your serotonin levels get too high. It’s not clear how many people get serotonin syndrome because most people with serotonin syndrome have mild symptoms and often don’t seek care.

Serotonin syndrome symptoms

Serotonin syndrome symptoms are caused by too much serotonin in your brain and body. This can cause many different symptoms, like sweating, fever, and confusion. Symptoms range from subtle and mild to severe or even life-threatening.

Mild serotonin syndrome symptoms

In the case of mild serotonin syndrome, symptoms can include:

Sweating
Shivering
Tremor
Fast heartbeat
Feeling anxious or restless
Nausea and vomiting
Diarrhea
Confusion
Agitation

Severe serotonin syndrome symptoms

In the case of severe serotonin syndrome, symptoms may include:

Fever
High blood pressure
Poor coordination
Involuntary movement
Muscle spasms or stiffness
Unusual eye movements
Hallucinations
Seizures
Loss of consciousness

Symptoms can show up within minutes of taking the medication. Other times, symptoms can take hours to appear. Most of the time, symptoms will begin within the first 24 hours after taking the medication.

If you have serious symptoms — or they seem to be getting worse — you should go to the emergency room or seek care from a healthcare professional right away.

8 medications and supplements that cause serotonin syndrome

Serotonin syndrome is rare. But the truth is, any medication that affects serotonin can potentially cause serotonin syndrome.

It’s most common with selective serotonin reuptake inhibitors (SSRIs) and selective serotonin-norepinephrine reuptake inhibitors (SNRIs) — mainly because these medications are widely used.

1. Antidepressants

Antidepressants are the most common medications that cause serotonin syndrome.

Monoamine oxidase inhibitors (MAOIs) aren’t used much anymore to treat depression, but they’re the most likely to cause serotonin syndrome. MAOIs include:

SSRIs and SNRIs are much more commonly prescribed to treat depression and anxiety. These medications are less likely to cause serotonin syndrome, but it’s possible, especially in people taking high doses in combination with other medications or supplements that release serotonin.

Common examples of SSRIs and SNRIs include:

Citalopram (Celexa)
Desvenlafaxine (Pristiq)
Duloxetine (Cymbalta)
Escitalopram (Lexapro)
Fluoxetine (Prozac)
Levomilnacipran (Fetzima)
Paroxetine (Paxil)
Sertraline (Zoloft)
Venlafaxine (Effexor)
Vortioxetine (Trintellix)
Vilazodone (Viibryd)

2. Herbal supplements

Some people use supplements to treat depression and mood disorders. Taking certain supplements along with prescription antidepressants can cause serotonin syndrome.

Supplements that affect serotonin include:

St. John’s wort
L-tryptophan
Ginseng
Nutmeg

3. Antibiotics, antifungals, and antivirals

Some antimicrobials (medications that kill germs) can cause serotonin syndrome when used by people who are also taking an SSRI or SNRI. So, be careful with antibiotics, antifungals, and antiviral medications, such as:

4. Pain medications

People taking SSRIs and certain pain medications can also develop serotonin syndrome.

Pain medications that increase serotonin levels in the brain include:

5. Antinausea medications

Antinausea medications can also increase serotonin levels. People taking SSRI or SNRIs should be careful when using:

6. Migraine medications

Medications called triptans, like sumatriptan and zolmitriptan, are used to treat migraine headaches. They can cause serotonin syndrome when taken with SSRI or SNRIs.

In 2006, the FDA warned that combining these two types of medications could cause severe serotonin syndrome. But, in a large 2018 data review, the number of people who were prescribed triptans and an SSRI or SNRI and ended up with serotonin syndrome (either actual or suspected) was very low — fewer than 1 in 1,000.

7. Illicit (illegal) drugs

Some illegal drugs can also cause dangerous levels of serotonin to build up.

Some of the most common types of street drugs that can lead to serious cases of serotonin syndrome include:

MDMA (3,4-methylenedioxy-methamphetamine, molly, ecstasy)
Methamphetamine (meth)
Cocaine

8. Over-the-counter medications

Two over-the-counter (OTC) medications that can raise serotonin levels in the brain are:

The risk is greater when certain medications are taken together. Nearly all of the serotonin syndrome cases happened because people took the OTC medications while taking other high-risk medications.

How is serotonin syndrome diagnosed?

Serotonin syndrome is a clinical diagnosis. This means the diagnosis is based on your symptoms and what a healthcare professional observes. There aren’t any blood tests or scans that can confirm the diagnosis of serotonin syndrome.

People can have a wide range of symptoms. So, healthcare professionals sometimes use tools to help understand if someone is having mild or severe symptoms. One tool commonly used is called the Hunter Serotonin Toxicity Criteria (HSTC).

Can serotonin syndrome go away naturally?

It’s possible that serotonin syndrome could go away naturally. If you stop taking the medication that’s causing serotonin syndrome, your symptoms will often go away on their own after 24 to 72 hours. This is more likely to happen if you have a mild case. You should stay in touch with your healthcare team, but it’s possible you won’t need any other treatment.

People with moderate to severe symptoms might need to have more treatment. When in doubt, talk with a healthcare professional. They can help you understand whether it’s safe for you to manage your symptoms at home or if you should seek medical care.

Serotonin syndrome treatments

The first treatment for serotonin syndrome is to stop taking any medication that increases serotonin levels in your body. But be aware: Suddenly stopping certain types of medications (like SSRI or SNRIs) can cause other symptoms, too. That’s why it’s important to check in with your prescriber before you make any changes.

In some cases, people with serotonin syndrome will need to go to the hospital for treatment.

Treatment may include:

Intravenous (IV) fluids
Oxygen therapy
Medications, including benzodiazepines and cyproheptadine, that help counteract the effects of excess serotonin

These treatments can help your symptoms get better and lower the effects of serotonin in your body.

Treatment is important because severe cases of serotonin syndrome are a medical emergency. Serotonin syndrome can also occasionally cause death.

How long does serotonin syndrome last?

It’s hard to say how long serotonin syndrome will last. Most of the time, serotonin syndrome will get better within 1 to 2 days after you stop taking the medication that caused it.

But sometimes, it can take longer for serotonin syndrome to go away. This is especially true if your symptoms were caused by a long-acting medication, like fluoxetine or selegiline. It can also take longer to recover if you have a severe case of serotonin syndrome. In these situations, your symptoms can continue for days or even weeks.

How can I prevent serotonin syndrome?

If you take medications that affect serotonin, make sure to:

Always point this out to your prescriber and pharmacist.
Avoid taking more than one medication that affects serotonin at a time, unless directed to do so by your healthcare team.
Use prescription medications only as prescribed, and avoid taking extra doses.
Check with your prescriber before starting OTC medications or supplements. They can help you make sure the medications or supplements don’t increase serotonin levels.

Frequently asked questions

Serotonin syndrome is rare, but it’s probably underdiagnosed. Underdiagnosis is especially likely for mild cases.

Serotonin syndrome can feel different depending on how severe the symptoms are. Symptoms can range from mild agitation with a racing heart and fast breathing to feeling like a full blown panic attack. In severe cases, muscle spasms, temperature and blood pressure dysfunction, and coma can be life-threatening.

Yes, too much serotonin can absolutely cause anxiety. Researchers think serotonin might act on a nervous network in the brain that regulates mood and feelings of anxiety.

The bottom line

Serotonin syndrome is caused by medications that affect the amount of serotonin in your body. Most cases are mild and go away within 24 to 72 hours after stopping the medication. However, some people can have more severe symptoms that require medical attention or even hospitalization.

Though serotonin syndrome is rare, you should keep an eye out for symptoms, especially if you take more than one medication that affects serotonin. And, if you’re concerned about serotonin syndrome, talk with a healthcare professional as soon as possible. They can help you use (and combine) medications responsibly. They can also help you to manage serotonin syndrome symptoms, in the rare chance that they do occur.

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Written by:

Sameer Hassamal, MD

Sameer Hassamal is an assistant professor of psychiatry at California University of Sciences and Medicine and Arrowhead Regional Medical Center. He is board certified in adult psychiatry, addiction psychiatry, and brain injury medicine by the American Board of Psychiatry and Neurology.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Frank Schwalbe, MD

Frank Schwalbe, MD, is an assistant professor of anesthesiology at the Yale School of Medicine. He has practiced anesthesiology for 30 years.

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References

Boyer, E. W., et al. (2023). Serotonin syndrome (serotonin toxicity). UpToDate.

Brain & Behavior Research Foundation. (2016). Serotonin triggers anxiety through newly discovered brain circuit.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.