Here’s what to know about serotonin syndrome

Serotonin—known as the body’s “feel good” chemical—is crucial for a number of different functions. But when it comes to serotonin, it’s possible to have too much of a good thing. A number of medications increase the body’s serotonin levels, and in very rare cases, this can lead to something called “serotonin syndrome” which can cause dilated pupils, confusion, and more serious effects. Serotonin syndrome doesn't happen often, but if you notice any signs of it, make sure to stop taking the medication right away and either contact your doctor or head to the emergency room.

Generally, serotonin syndrome occurs when you take more than one type of medication (or supplement) that increases your serotonin at the same time. Remember: Most medications that affect your serotonin levels are completely safe, and your doctor will help you minimize the risks of having too much. But if you or a loved one ends up with too much serotonin in their system, it can be helpful to know what to look out for.  

In this article, we’ll talk more about the different roles serotonin plays, explain how serotonin syndrome happens, and how to treat and prevent it.

Understanding serotonin

Serotonin is a brain chemical derived from the amino acid tryptophan that carries signals between nerve cells throughout your body. It’s an important player in many different body and brain functions, especially your mood.  

At normal levels, the presence of serotonin can help you feel focused, emotionally stable, happy, and calm. Low levels of serotonin are associated with depression (though it’s not the only cause) which is why so many medications used to treat anxiety, depression, and other mood disorders target ways to increase or balance serotonin levels in your brain.  

Serotonin’s role in a number of different bodily functions  

Here’s more on what else serotonin does.

• Digestion: Serotonin helps control bowel function and plays a role in protecting your gut. It can control how food quickly moves through your body, and also help reduce your appetite while eating to help you know when you’re full.  

• Sleep: Serotonin (along with another neurotransmitter called dopamine) affects how well and how long you sleep. Your brain also requires serotonin to make a hormone called melatonin that regulates your sleep-wake cycle.  

• Wound healing: When you have any kind of tissue damage, platelet cells in your blood release serotonin to help heal the wound. This helps wounds stop bleeding and accelerates wound healing.  

• Nausea: In response to illness, foods, or other conditions, serotonin in the stomach can initiate nausea and vomiting. This is why many drugs used to reduce feelings of nausea and vomiting target specific serotonin receptors in your brain.

• Sexual health: Along with other chemicals like dopamine, serotonin plays a role in your desire for sex. High levels of serotonin tend to indicate a low libido, while low levels of serotonin correspond with a high libido.  

What is serotonin syndrome?

Serotonin syndrome is a potentially life-threatening condition that happens when you have too much serotonin in your body. This can happen when you take medications that build up levels of serotonin or increase your sensitivity to it.  

There are a number of medications and supplements that can affect serotonin levels, not just antidepressants—but also common drugs prescribed for nausea and pain. Most people are able to take these medications safely when they follow their doctor’s instructions and stick with the appropriate dosage. In fact, serious cases of serotonin syndrome are rare, and most cases don’t require medical intervention beyond stopping medication or decreasing the dose. It’s unclear how many people actually get serotonin syndrome, and most cases are so mild that people don’t seek medical care.  

However, severe cases of serotonin syndrome can be life-threatening. It typically happens when you start a new medication or take an increased dose of one that increases the level of serotonin in your body. For this reason, any changes to your medication routine should be discussed with and supervised by your doctor.

Serotonin syndrome symptoms  

The buildup of serotonin in your body can cause many different symptoms that can range from subtle to mild to severe and even life-threatening. Symptoms tend to show up quickly, usually within 24 hours but sometimes as soon as an hour.

Mild symptoms

• Nervousness
• Nausea, vomiting
• Diarrhea
• Dilated pupils
• Tremor  

Moderate symptoms

• Agitation
• Restlessness  
• Muscle twitching, involuntary muscle contractions, muscle spasms, muscle rigidity
• Sweating, shivering
• Abnormal eye movements

Severe symptoms

• Confusion, disorientation, delirium
• Rapid heart rate
• High blood pressure
• High body temperature  
• Seizures
• Abnormal heartbeat
• Passing out, fainting

If you have severe symptoms or your symptoms seem to worsen over time, call a doctor right away or go to the emergency room.  

How long does it last?

In most cases, serotonin syndrome symptoms will go away within 24 to 72 hours after stopping the new medication or decreasing the dose.  

What causes serotonin syndrome?

While serotonin syndrome is rare, it’s true that any medication that increases the body’s serotonin levels can potentially cause the condition. It usually happens with two types of antidepressants—selective serotonin reuptake inhibitors (SSRIs) and selective serotonin-norepinephrine reuptake inhibitors (SNRIs)—but mostly because these medications are so widely used, and not because of any issues with their safety.  

But other medications can cause serotonin syndrome, too, though they won’t usually cause serotonin syndrome on their own. Most cases of serotonin syndrome occur when people take two or more medications that affect serotonin at the same time.

Other situations that might increase levels of serotonin include:

• Taking too much of one serotonin-related medication, accidentally or on purpose
• Taking certain herbal supplements  
• Increasing your dosage of certain antidepressants  
• Using any illicit drugs known to increase serotonin levels

What medications affect serotonin?

A number of over-the-counter drugs, prescription medications, and supplements can affect your serotonin levels. Here’s a look at some examples.

Antidepressants  

• SSRIs including citalopram (Celexa), fluoxetine (Prozac), fluvoxamine (Luvox), escitalopram (Lexapro), paroxetine (Paxil, Pexeva, Brisdelle) and sertraline (Zoloft)
• SNRIs including desvenlafaxine (Pristiq), levomilnacipran (Fetzima), milnacipran (Savella), duloxetine (Cymbalta, Drizalma Sprinkle) and venlafaxine (Effexor XR)
• Tricyclic antidepressants including amitriptyline and nortriptyline (Pamelor)
• Monoamine oxidase inhibitors (MAOIs) including isocarboxazid (Marplan) and phenelzine (Nardil)

Antidepressants are safe to use, and your doctor will help you minimize the risks of serotonin syndrome by asking what else you’re taking.

Other medications  

There are a number of other medications that affect the body’s serotonin levels, especially when combined with other drugs that do so as well. These medications include:  

• Pain medications, such as opioid pain medications including codeine, fentanyl (Duragesic, Abstral, others), hydrocodone (Hysingla ER), meperidine (Demerol), oxycodone (Oxycontin, Roxicodone, others) and tramadol (Ultram, ConZip) ‍
• Over-the-counter cough and cold medications containing dextromethorphan (Delsym) ‍
• Anti-migraine medications including carbamazepine (Tegretol, Carbatrol, others), valproic acid and triptans, which include almotriptan, naratriptan (Amerge) and sumatriptan (Imitrex, Tosymra, others) ‍
• Ritonavir (Norvir), an anti-retroviral medication used to treat human immunodeficiency virus (HIV) ‍
• Anti-nausea medications including granisetron (Sancuso, Sustol), metoclopramide (Reglan), droperidol (Inapsine) and ondansetron (Zofran) ‍
• Lithium (Lithobid), a mood stabilizer

Herbal and dietary supplements and illegal substances  

Unregulated products and natural supplements can also affect your serotonin levels and cause serotonin syndrome. These include:  

• Herbal supplements including ginseng, St. John’s wort, Syrian rue, and nutmeg
• Other dietary supplements including 5-HTP and tryptophan
• Illegal substances including ecstasy, LSD, cocaine, amphetamines, and methamphetamines

What to do if you have excess serotonin

While there aren’t any specific tests to diagnose serotonin syndrome, a doctor will usually be able to make the diagnosis based on your medical history—including the history of medications you take that affect serotonin levels—a physical examination, and a review of your symptoms. It can help if you prepare for your visit with your provider by bringing in a list of all the medications and products you take, including prescription medicines, over-the-counter medicines, supplements, and illegal drugs. Talking about these things can sometimes make you feel uneasy, but it's important to remember that your doctor is here to help and support you, not judge you.

In order to rule out other possible conditions and establish a treatment that works, your  doctor may order:  

• Blood and urine tests
• Tests to look for signs of infection, including a spinal tap
• Other tests including chest X-ray or CT scan, as needed  

The treatment for serotonin syndrome depends upon the severity of your symptoms.  

Treatment based on symptoms

• Mild symptoms: For mild cases of serotonin syndrome, stopping the medication or decreasing the dosage will usually be enough for symptoms to go away within 24 to 72 hours. If necessary, you may be given a serotonin blocker such as cyproheptadine (Periactin).  
• Moderate symptoms: If you have a moderate case of serotonin syndrome you’ll be observed in the hospital for at least 24 hours to make sure your symptoms are improving with treatment.
• Severe symptoms: In severe cases of serotonin syndrome, you’ll be admitted to the intensive care unit (ICU), where your body and organ function can be closely monitored.  

Remember, never stop taking your medication or change your dose without first talking to your doctor. Try to take your medication as usual and, if you have worsening symptoms, seek emergency care.  

How do you prevent serotonin syndrome?

To prevent serotonin syndrome, it’s crucial to closely keep close tabs on all your medications, especially if they increase serotonin levels in the body. Make sure you have a complete list of what you’re taking—including any supplements—and share them with your doctor. In fact, when a doctor or psychiatrist prescribes you a new medication, they will likely ask about it. This helps them identify any potential interactions and adjust your treatment accordingly.  

Then when you start a new medication, pay close attention to how your body reacts. Let your doctor know right away if you notice any unusual symptoms. Remember, it’s okay to ask questions. Your doctor’s goal is to minimize any risks, including for serotonin syndrome, to make sure you can take medication safely and start feeling better soon.