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Serotonin Syndrome Symptoms & Signs

Serotonin syndrome is a potentially fatal condition resulting from abnormally high levels of serotonin in the CNS. This may be caused by using various drugs that influence the neurotransmission of serotonin in the brain such as SSRIs, MDMA, various opioids, and even natural substances such as 5-HTP and St. John’s Wort. Typically it is only caused by serotonin-influencing drugs at high doses and/or by taking multiple drugs that influence serotonin.

Many people treating mood disorders with antidepressants are typically advised to avoid taking multiple SSRIs at the same time. This is why competent doctors will not prescribe multiple SSRIs simultaneously.  Even when utilizing an antidepressant augmentation strategy, an SSRI is always prescribed with a non-serotonergic drug in order to avoid this condition. Taking multiple drugs that act on serotonin is the most likely culprit for causing serotonin syndrome, but it can occur with abnormally high doses of various drugs and/or adverse reactions.

Since serotonin syndrome can be life-threatening, many professionals refer to it as “serotonin toxicity” because it is essentially poisoning the body. The elevated levels of serotonin end up resulting in an array of unwanted mental and physical symptoms. In some cases, the symptoms may be difficult to detect, while in other cases they may result in extreme, noticeable sickness.

Serotonin Syndrome Symptoms: List of Common Signs

It can be difficult to distinguish serotonin syndrome from medication side effects as well as other naturally occurring symptoms. The most prominent symptoms of this condition tend to be: tremors, confusion, akathisia, and involuntary muscle contractions and/or reflexes. Other common symptoms tend to include: fever, pupil dilation, diarrhea, sweating, and increased heart rate.  These symptoms can occur within minutes or hours of taking a serotonergic agent.

  • Agitation: When serotonin levels rise, it can lead a person to feel agitation or increased feelings of nervousness. This is a relatively standard side effect of many serotonergic psychotropic drugs, so this as a standalone symptom wouldn’t necessarily indicate serotonin syndrome.
  • Aggression: People with excess serotonin may become more aggressive than usual. A person experiencing serotonin syndrome will likely notice that they suddenly feel or behave more aggressive than normal.
  • Akathisia: Sometimes people will appear to be unable to sit still and restless. If they feel an inner restlessness and are constantly moving around, it could be a sign of akathisia, which can occur as a symptom of serotonin syndrome.
  • Coma: In very severe cases, serotonin syndrome can lead a person to coma or unconsciousness. Although it is relatively rare for elevated serotonin to induce coma, it has happened. This may also be accompanied by changes in breathing and/or suspended breathing.
  • Confusion: Mental confusion is another common occurrence for those experiencing serotonin syndrome. You may be unable to think clearly, have difficulty with short-term memory, and changes in thinking and perception. In mild cases, the confusion may not be much of a factor, but in more severe cases, it may be strikingly noticeable.
  • Diarrhea: In certain cases people react to the serotonin overload with diarrhea. Generally this symptom can be a side effect from medication, but if accompanied by several other common symptoms, it may signal a problem.
  • Dilated pupils: Another tell-tale sign of serotonin syndrome is the dilation of pupils. If you begin experiencing a fever, notice that your pupils dilate, accompanied by tremors, it’s a good chance that excess serotonin is the culprit.
  • Dry mouth: Lack of saliva throughout the mouth is sometimes another sign that a person has this condition. This is a very common side effect associated with antidepressants, so as a standalone symptom, it doesn’t suggest much. However, when coupled with several of the more notable symptoms, it could be an indication of this condition.
  • Fever: A common sign of serotonin syndrome is that of an increased body temperature or fever. In general, more severe cases of this condition tend to result in a higher fever, while less severe cases may result in a mild fever. It is also possible to have the condition with no recorded fever.
  • Hallucinations: In some serious cases, people may experience hallucinations as a result of serotonin level increases. When serotonin levels increase to a high level, it is thought that the metabolites within the serotonin can contribute to causing hallucinations.
  • Headache: Many individuals end up experiencing headaches when the level of serotonin in their CNS is abnormally high. Headaches are a common symptom of many conditions, but can also be an indication of serotonin syndrome.
  • High blood pressure: Increases in blood pressure have been reported as well. If you suspect serotonin syndrome and your blood pressure is higher than usual, it could be a sign.
  • Hypomania: This is characterized as a low-grade euphoria or elevated mood and increased energy. High levels of serotonin can contribute to causing hypomania, even among individuals without bipolar disorder. If you have no prior history of hypomania, it could be a result of serotonin syndrome.
  • Increased heart rate: Have you noticed changes in your heart rate? If your heart rate increases, this could be a result of serotonin elevations.
  • Insomnia: Another symptom that some people experience is that of insomnia or the inability to fall asleep. If you are twitching, can’t seem to sleep, and have a fever – it could be a result of the serotonergic medication that you are taking.
  • Muscle twitching: A common sign of serotonin syndrome is excessive muscle twitching. You may notice that certain areas of your body begin to twitch. If you are on a high dose of a serotonergic drug and/or have combined serotonergic medications, it is likely an indication of serotonin syndrome.
  • Nausea: People can become nauseated and feel as if they are going to vomit. In some cases it is possible to become sick and actually vomit as a result of this condition. With that said, nausea is not observed in all cases of this syndrome.
  • Overreactive reflexes: You may notice that your reflexes become hypersensitive and more reactive than usual. This is somewhat related to the physical tremors that are often observable.
  • Shivering: Your body may start to shiver and you may not know what could have caused it. The shivering may appear to be similar to when a person gets sick with a viral infection. In fact, many people mistake the shivers resulting from serotonin syndrome as a sickness.
  • Sweating: Many individuals with serotonin syndrome will notice an increase in sweating. They may begin to sweat profusely and be unaware that it’s a result of the increased serotonin. In other cases though, a person won’t sweat – therefore this isn’t always a necessary symptom.
  • Tremors: One of the more prominent symptoms of serotonin syndrome is that of tremors or shakes throughout the body. Someone who has taken multiple serotonin-acting drugs may notice that their body shakes uncontrollably which suggests serotonin-syndrome.
  • Vomiting: A person with serotonin syndrome may become noticeably sick and start to vomit.  They may think that they are becoming sick with a virus or bacterial infection, when in reality the sickness is caused by the elevated serotonin levels.

Note: It is important to note that many of these symptoms may occur as standard side effects of a drug or drug interaction. Doctors may have a difficult time diagnosing serotonin syndrome unless a patient reveals that they’ve taken multiple agents that influence serotonin (e.g. 5-HTP and an SSRI). If you have taken multiple serotonergic agents, be sure to report it to your doctor so that they can properly treat the condition.

If you suspect serotonin syndrome…

If you suspect that you have serotonin syndrome, be sure to seek immediate medical attention. The condition is typically treated with antihistamine drugs such as cyproheptadine, which acts as a serotonin antagonist. Serotonin antagonists inhibit serotonin action on the 5-HT receptors and help reduce the possibility of serotonin syndrome.

Other individuals may need to be treated with activated charcoal in order to rid the body of the serotonergic drugs. A doctor will decide how to treat the condition based on the severity of the symptoms that a patient is experiencing. In cases in which a person is exhibiting hyperreflexivity and/or tremors, benzodiazepines may be temporarily administered to manage the problem.

In other cases, atypical antipsychotics may be administered to help with the antagonism of serotonin. Once the condition is treated, a patient and doctor will be able to come up with an idea of what caused it. It could have been from too high of an SSRI dose, an attempted overdose, and/or mixing of serotonergic drugs (most common).

Personal story: Taking Paxil and Prozac Together

When I was 16 or 17, I was taking Prozac, but also had some Paxil leftover. Since I was desperate to find a drug or combination of drugs that worked, I decided to take both Paxil and Prozac before school. To my surprise, the combination of the two drugs helped my depression more than each as a standalone treatment. I noticed that I felt more energetic than usual, experienced a mild hypomania, and shivers.

When I got home, I felt more shivers, and felt as if I may have a slight fever. It didn’t feel the same as getting sick with a virus, but I didn’t feel good. I actually took the same combination for another day and then finally Google searched, “Taking Prozac and Paxil at the same time” or something like that. I read about it and realized that it can cause serotonin syndrome…

At the time I had no clue what serotonin syndrome was and if it could even be bad. I didn’t read too much into it and actually didn’t really care if I experienced it as long as my medications were working. Fortunately I posed up in a forum at the time and got huge warnings from many people about the dangers of taking both SSRIs simultaneously. Upon realizing the dangers of serotonin syndrome, I immediately stopped combining these drugs.

Fortunately I must’ve had a mild case of serotonin syndrome, because I never got really sick, ended up with a high fever, and I’m only speculating that I had a mild fever in the first place. Had I been warned about serotonin syndrome and about the dangers of mixing SSRIs, I never would have taken the risk. I guess my doctor assumed that I was just taking one medication.

Beware of serotonin syndrome… never take multiple SSRIs

Many people are simply unaware that this condition occurs when they combine multiple serotonergic antidepressants (e.g. taking Zoloft and Prozac). Most doctors don’t inform patients that they can’t take natural supplements like 5-HTP or St. John’s Wort with an SSRI or SNRI medication. Other patients may try experimenting to treat their depression by taking multiple SSRIs such as Prozac with Lexapro.

If they suspect that these are just side effects of combining the drugs rather than an indication of a more serious condition called serotonin syndrome, they may keep it up for many days. Doctors should always inform patients of the consequences associated with mixing antidepressants and take specific note of any serotonin-influencing supplements that a patient may be taking throughout treatment.

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{ 3 comments… add one }
  • Jim November 18, 2016, 6:15 am

    I was on Effexor XR for 10 weeks. The good news is that it got me into remission for my anxiety and depression. It worked so well that before long I developed a mild case of serotonin syndrome, even with a low dose of 37.5 mg. My symptoms are hypomania and nervousness/agitation. I tapered and my last dose was 3 weeks ago.

    I’m still experiencing symptoms of the syndrome. My MD said it can take awhile for the serotonin activity to return to normal. I’m hoping in another week or two it will be over. Considering I’m in remission from anxiety and depression I shouldn’t complain too much.

  • Alicia Kaster August 22, 2016, 1:26 am

    Hello, I was writing you all a comment on the natural approach the supplement 5HTP, this drug actually gave me some problems. I was taking it for two weeks and one night I started to have some problems shaking, rapid heartbeat, and other symptoms, that night I was rushed to the hospital only to find out that my Serotonin level was extremely high and it was from this supplement.

    The physician told me to immediately stop taking this drug because it was unsafe and really hadn’t been tested for use, so I strongly advise people who think this is the safer route to ask a physician first. I was lucky that night when I was in the ER, I could have died as a result of listening to a health food store sales person. Thanks.

    • Greg December 18, 2017, 5:33 am

      Hi Alicia and thank you for your post. Were you combining the 5-htp with any other drugs such as antidepressant or SSRI? Were you drinking alcohol on a daily basis? I have done a lot of research and I have never heard of this happening while taking the 5-htp supplement as a standalone.

      When shakes do you mean you were cold or you were have tremor? Honestly I don’t think that this was serotonin syndrome that you were experiencing… YouTube serotonin syndrome – this is a pretty serious thing, like a seizure… much different than chills or shakes.

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