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High Serotonin Levels: Symptoms & Adverse Reactions

Serotonin (5-HT) is a neurotransmitter that most people associate with mood. It is a derivative of tryptophan and is present throughout the body in the CNS, GI tract, and blood. Most people have heard that if you have low serotonin, you’re more likely to be depressed, but not many have heard of high serotonin. While normal serotonin production can help maintain a balanced mood, promote relaxation, and help improve memory – some people end up with high serotonin.

Those that end up with high serotonin levels typically take either drugs and/or supplements that artificially elevate low serotonin. Since low serotonin is problematic, high serotonin must be the exact opposite right? Not necessarily. Slightly elevated serotonin can help those with major depression – which is why an SSRI medication is considered a first-line treatment option.

Although moderate serotonin levels are beneficial for healthy brain function, abnormally high serotonin production can lead to an array of problems as well. High serotonin is typically caused by serotonergic pharmaceutical drugs, supplements, and certain illicit drugs. If you suspect you have high serotonin, it is important to seek medical attention as it could be fatal.

High Serotonin Levels (Symptoms)

Those that have ever taken multiple serotonergic agents (intentionally or unintentionally) have likely experienced mild to moderately high serotonin. Below is a list of symptoms that you may experience if your serotonin level is elevated beyond the norm.

  • Agitation: Some people experience an increase in inner restlessness or feel agitated when serotonin levels become too high. This may seem counterintuitive as low levels can also lead to agitation, but abnormally high levels can produce the same effect. You may be unable to sit still and feel nervous.
  • Dilated pupils: Those that have elevated levels of serotonin may find that their pupils are more dilated than usual. This increased dilation is caused by muscle groups in the iris becoming heavily activated as a result of the high serotonergic stimulation.
  • Dizziness: Some people report feeling more dizzy than usual when their serotonin levels increase. If the dizziness becomes severe, it may be a sign that you need to seek immediate medical attention. High levels of serotonin is known to produce a cascade of unwanted physiological symptoms.
  • Fatigue: Some people notice that they feel drowsy, sleepy, or have a lower than average energy level when their serotonin is high. While the effects of serotonin increases are subject to individual variation, those that have high amounts may feel depleted of energy or become increasingly tired.
  • Goose bumps: Another obvious sign that your serotonin levels are too high is that you have goose bumps across your skin. This may be directly related to shivering, body temperature changes, and altered nervous system function.
  • Headache: A common symptom of high serotonin levels is a headache. The headache you experience may be mildly uncomfortable or severe to the point that it makes you feel sick. Generally the headache will be accompanied by other symptoms if too much serotonin is the cause.
  • High blood pressure: High levels of serotonin can increase your blood pressure, and in some cases, may cause a permanent condition known as pulmonary hypertension. Serotonin has been directly linked to causing certain types of hypertension. It is recommended to keep serotonin levels within a safe range.
  • Hypomania: Some people may experience hypomania as a result of a serotonin increase beyond normal means. This may occur in individuals with bipolar 2 disorder, but others may experience it as well. The serotonin system is funny in that some people who are non-bipolar experience hypomania with administration of serotonin raising drugs.
  • Mania: This is characterized by significant talkativeness, socialization, euphoria, and risky behaviors (e.g. excess spending). In some people, mania may be triggered by high levels of serotonin. While mania may be more likely to occur among those with bipolar disorder, artificially elevated serotonin as a result of pharmaceuticals may also cause temporary mania.
  • Rapid heart rate: It is common for a person’s heart rate to increase when their serotonin level becomes too high. If you notice a change in your heart rate, you should enlist the help of a medical professional to get the serotonin level lowered.
  • Relaxation: For certain individuals, the relaxation response is enhanced by mild to moderate elevations in serotonin. This is what tends to reduce various types of anxiety and phobias. The serotonin elevation helps a person stay calm and remain relaxed in situations that would otherwise stress them out.
  • Restlessness: Some people may become excessively restless and unable to sit still. This may be accompanied by poor balance and coordination, despite the fact that the person is unable to remain calm. It may also be fueled by an inner sensation of agitation.
  • Shivering: Since serotonin plays a role in temperature regulation, some people may feel hot and cold flashes, notice changes in body temperature, and start to shiver. Shivers are a common sign that a person has artificially elevated their serotonin levels to an extreme.
  • Sweating: You may start to sweat excessively with high levels of serotonin. This is due to the fact that your brain and nervous system doesn’t know how to handle the abnormally high amount of this neurotransmitter. Profuse sweating should subside when the serotonin level is decreased.
  • Weight gain: Many people end up gaining weight on medications that elevate serotonin. (Read: “Antidepressants and Weight Gain“). High levels of serotonin may affect the metabolism, motivation, as well as energy levels – making people feel lazier than they should.

Note: Keep in mind that the number of symptoms you experience and severity of each symptom will be subject to individual variation. Each person is different and will likely experience individualized reactions to the serotonin elevation.

High Serotonin Adverse Reactions

Understand that high serotonin levels can lead to a condition known medically as “serotonin syndrome.” This is a condition that can be fatal if it isn’t treated immediately. If you suspect that your serotonin levels are too high, a medical professional should be able to help.

  • Confusion: A serious symptom that may emerge is that of mental confusion. The person may struggle with memories, conversation, and may appear to be acting drugged or downright goofy. This increased mental confusion may make it difficult for the person to perform even menial cognitive tasks.
  • Death: The reason you need to seek immediate medical help if you suspect high serotonin is to avoid death. In some cases, high levels of serotonin are fatal and could end a person’s life. Always go into the doctor or emergency room if you have taken multiple serotonergic drugs as a combination.
  • Diarrhea: Some people develop severe bouts of diarrhea from serotonin toxicity. This is a neurotransmitter that is found in the GI tract and may be involved in digestive processes. Too much serotonin disrupts the GI tract and can result in us feeling sick with diarrhea.
  • Fever: It is common to experience changes in body temperature as a result of serotonin syndrome. You may feel physically chilled and experience body shivers, but you may simultaneously be running a fever. If you have a fever, this is a sign that your body isn’t able to handle the serotonin increase.
  • Irregular heartbeat: It was already mentioned that you may experience an increased heart rate, but you may also experience an irregular heartbeat – which is problematic. An irregular heartbeat may put excess strain on your heart functioning. This is a sign that you need to be medically evaluated.
  • Loss of balance: If you feel as if you cannot properly walk or maintain balance, this is another sign of too much serotonin. There is often significant interference in our coordination when we have high levels of serotonin in the brain.
  • Muscle twitching: Your muscles may twitch excessively as a result of serotonin elevations. If you notice that certain parts of your body start to twitch, realize that it’s probably a result of serotonin toxicity.
    Seizures: In extreme cases, some people respond to serotonin increases by having seizures. To prevent a seizure, it is recommended to do whatever you can to lower your serotonin as quickly and as efficiently as possible.
  • Unconsciousness: Some people may end up fainting or becoming unconscious if serotonin levels rise too high. If you feel faint or as if you may pass out, it’s best to get into the emergency room as soon as possible.
  • Vomiting: Some people end up feeling so nauseous with flu-like symptoms that they end up vomiting. While vomiting may be good in that it could clear some serotonin-based drugs from the system, this is a sign that a person needs immediate medical intervention.
  • Weakness: Feeling physically weakened as if you’ve lost all your strength is a clear sign of an adverse reaction. You may tremble or feel as if you cannot walk without collapsing.

How To Decrease Serotonin Levels

There are several ways in which you can decrease your levels of serotonin. Keep in mind that if you suspect serotonin syndrome, seek immediate medical attention. Other recommendations are provided for those who want to systematically lower the effect of serotonin on their functioning.

  • Activated charcoal: An obvious intervention for preventing high serotonin after ingesting too many antidepressant drugs or a combination is that of activated charcoal. However, in order for activated charcoal to have any effect, it must be taken within 30 minutes of the ingestion of the serotonergic agent. If it isn’t taken within a close proximity of the serotonergic agent, it may not be effective. This is an immediate intervention strategy should a person attempt to overdose.
  • Dietary interventions: Certain dietary strategies can help you reduce the amount of serotonin in your system. Including substances like gelatin and collagen are thought to help decrease the production and absorption of serotonin. Additionally you can lower the number of foods that you eat containing tryptophan (which your body converts into serotonin). A lower carbohydrate, higher protein diet should help reduce endogenous serotonin levels.
  • Drugs: There are several drugs that doctors will administer patients with abnormally high levels of serotonin. Most commonly administred are 5-HT2A antagonists which help reverse the effects of serotonin toxicity. A couple of commonly used 5-HT2A antagonists that doctors prescribe for individuals with abnormally high serotonin include: Cyproheptadine and Chlorpromazine.
  • Supplements: If you want to decrease serotonin levels over time, you could supplement BCAAs (branch chain amino acids). These seem to be effective at inhibiting the uptake of tryptophan in the brain. The only problem you may run into is that they also affect other amino acids like tyrosine. You may also want to consider supplementing L-Tyrosine or a dopaminergic substance as it may counteract the effects of serotonin.

Conditions associated with High Serotonin

There are several conditions and situations in which a person may end up with abnormally high serotonin. The most common cause of high serotonin is from taking antidepressants.

  • Depression treatment: If you’re on an antidepressant, but decide to take another one along with it, you may experience serotonin syndrome. Mixing multiple antidepressants or exceeding the recommended dosage guidelines of your current medication may result in symptoms associated with high serotonin.
  • Illicit drug use: Some people that use illicit drugs aren’t aware of the fact that they could end up experiencing serotonin syndrome. This is a risk with certain stimulants (e.g. MDMA), psychedelics (e.g. LSD), and various opioids (e.g. Oxycodone). While most people do not end up experiencing serotonin syndrome from a low dose of illicit drugs, higher doses and/or interaction effects can produce high serotonin.
  • Osteoporosis: After prolonged use of serotonin-based antidepressants, people can develop osteoporosis. This is due to the fact that when serotonin levels increase in the intestinal tract, it leads to bone loss. In addition increases in serotonin also lead to increased secretions of prolactin and cortisol – which remove calcium from the bone. This leads to weakened bones and hardened arteries.
  • Overmethylation: This is a condition caused by an SNP (polymorphism) of the MTHFR gene.  Those that are “overmethylators” tend to create abnormally high levels of neurotransmitters such as serotonin.  Blood tests reveal that overmethylation tends to also result in high levels of copper, low histamine, and low zinc.  While serotonin syndrome isn’t likely, a person may experience a reduced libido, low motivation and energy, as well as a depression caused by high serotonin.
  • Pulmonary hypertension: There is significant evidence to support the idea that high levels of serotonin can cause pulmonary hypertension. Serotonin elevations lead to constriction of the blood vessels and thickening of the heart valves. Long-term elevations of serotonin is a likely contributor to this condition.
  • Serotonin syndrome: Obviously the most common condition associated with high serotonin is that of “serotonin syndrome.” This is a potentially fatal condition stemming from too much serotonin within the central nervous system. Serotonin syndrome can affect a person’s cognitive function, coordination and balance, and result in flu-like symptoms.

Have you experienced high serotonin?

If you’ve had an experience in which you’ve experienced high levels of serotonin, feel free to share it in the comments section below. Awhile back I had experienced abnormally high serotonin as a result of taking Prozac and Paxil together. I was unaware that this could actually be a deadly combo. Fortunately I was on relatively low doses of each and I’m thinking I experienced a moderate elevation in serotonin.

This resulted in me feeling slightly hypomanic, I had a pounding headache, felt dizzy, and somewhat disoriented. I also recall experiencing goose bumps and had a slight temperature change. It was pretty uncomfortable, but at the time I figured it was probably just side effects from the drugs and not any serotonergic contraindication.

Most people that experience a serotonin overload do so accidentally as a result of taking multiple serotonergic antidepressants together or taking an SSRI with a supplement like 5-HTP. It is important to be aware of the fact that serotonin elevations can certainly help someone with depression, but abnormally high levels can be dangerous and detrimental to a person’s health.

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{ 18 comments… add one }
  • Natália January 19, 2016, 8:51 pm

    Hello, my last blood test found high levels of serotonin, but I don’t use drugs, and I am not taking any medicine. I would like to understand that. Thank you.

  • Elizabeth Duval January 30, 2016, 4:22 pm

    Hi Natalia. I recently have had a blood test showing that I have elevated serotonin levels. I am now undergoing other testing in order to rule out carcinoid cancer. Carcinoids will raise serotonin levels. It might be prudent to talk to your physician more about this… and there is lots of info on the internet. Blessings, Elizabeth

  • M.R. March 3, 2016, 5:50 pm

    Hi, After reading the book LIGHTS OUT, I seem to relate to the idea of having high serotonin and low dopamine. I believe high serotonin will make one feel more anxious – not the ‘well being’ that is often associated with serotonin.

    • Olga May 18, 2016, 5:30 am

      You’re correct. Look into a letter written by a Beat Generation writer and recreational drug user, William Burroughs, I think the title is called “Master Addict” or something. Even back in his day, he had more information about how drugs affect our brains than I have ever had from any doctor or school health class.

      We tend to lump all “drugs” into one category, but they’re not. There’s the ones that make you manic and schitzy, and the ones that just calm you down. The dopamine/serotonin difference is what draws the line between them. Any doctor that offers you an SSRI for anxiety should be labeled a fraud and treated like a the snake oil salesman he is.

  • Derek March 15, 2016, 6:56 am

    I was taking cymbalta and amitriptyline and after 2 days I woke up with extreme burning tingling in my chest and legs… the room felt like it was enclosing on my head 10x faster than normal. I knew there was a problem when my pupils were so dilated that they blacked out my entire eye. Followed by severe headache, twitching, fever, cold sweats, rapid heart rate, then slow irregular heart beat finally sever chest pain, it lasted for about 3 days and was the scariest shit I have had. I will never take that medication again, I also was taking 80mg of oxycodone with it everyday…

  • Ian June 14, 2016, 2:48 pm

    I’ve been taking antidepressants for muscle tension headaches and recently bought Rhodiola Rosea. Within 10 minutes of taking it I started to faint and my blood pressure was 45. Thought I was breathing my last. Thanks for the info about Serotonin Syndrome.

  • Dana Murdock July 1, 2016, 9:30 am

    Here is my experience with having too much serotonin. I have had serotonin toxicity 4 times. In my youth from MDMA, which had the exact opposite effect on me. I felt extreme agitation and frustration, I isolated and shook for hours where my friends were experiencing euphoria. The second time was from a non narcotic pain reliever for a spinal injury and my reaction was notable but mild (ultram), next in an attempt to deal with the same neuro damage in my spine I was given a tricyclic.

    After several hours I couldn’t move, had lock jaw and could not call for help. I was alone. It took two days before I could get out of the trance. I went to the ER as soon as I could and they thought I was crazy. :/ I went back to my doctor, this time armed with my neurologist step father, who believed that I had a bad experience with the tricyclic. After conferring with my doctor I reluctantly agree to try Cymbalta.

    Dad stayed with me. Within 20 minutes of taking one Cymbalta, my eyes began to shake, I got lock jaw, could not speak, felt trapped in my head and had little control over my body. I got to the ER and was rushed through. I had a temp of 104 and was given two medications to fix me. I felt like a rhino being taken down by a dart in the desert. I was on the mend within an hour although I did not feel better for several days.

  • Diana Howell July 6, 2016, 9:39 pm

    I have muscular dystrophy, and my neurologist has me on a Fentanyl patch (100 mcg) and Oxycodone for the pain associated with it. Along with that, I had begun experiencing anxiety and depression due to menopause. Seeing my GP for this issue, he started me on both Prempro (HRT) and Lexapro (an antidepressant).

    I lasted maybe six weeks taking the Prempro, as the nausea side effects were worse than the hot flashes. However, I continued taking the Lexapro with the belief it would greatly help with my depression. Big mistake. When I initially contacted my physician (when he gave me the prescriptions) that I ran a drug interaction checker on the internet that indicated a severe problem taking the Lexapro along with the Fentanyl and Oxycodone, he got on the phone and literally snapped at me.

    ‘You think Dr. Google knows more than me? I wouldn’t have prescribed anything that would interact with your pain killers’. So… I kept taking the Lexapro along with everything else, believing he knows best. But this afternoon when I could barely take two steps due to lack of strength, and my legs feel like jello, am discovering from Internet research that I probably have a severe case of serotonin syndrome.

    The only thing I can think to do is stop taking the Lexapro immediately and hope my legs regain their strength in time. And find another family physician.

    • Jaykay September 5, 2016, 4:45 pm

      Some of these so called doctors are a disgrace. I’ve found searching on Google to be much more helpful. But you must find a GP out there who genuinely cares.

      • Laura October 17, 2016, 9:10 pm

        So true!

  • Calvin Maupin September 2, 2016, 1:48 am

    I have had serotonin syndrome twice, and both times was not diagnosed with it because I did not run a high temperature, nor got nauseous. I believe this is because I have no Thyroid, because of this I have lived with a continues high level of serotonin that would cause me all kinds of problems if I take about any kind of medicine. The last time I had serotonin syndrome I had close to 30 side effects.

    I have had close to 7 doctors that does not believe I have serotonin toxicity, and have not bothered to even test me for this problem. Can you inform me of a research institution that may be interested in helping me? Somebody needs to let doctors know how serious of a problem serotonin is becoming, as far as, more people coming down with serotonin toxicity, and serotonin syndrome!

  • Nicole September 3, 2016, 3:38 am

    Good to know I’m not alone or crazy. I NEVER had a good experience on E or MDMA the very few times I tried it. I just thought I was allergic to it or something, the same thing would always happen. I had intense body highs, I would throw up, I felt like I was going to die, I became introverted, and was always inside my head trying to calm myself down and convince myself I was not dying.

    My psychiatrist put me on 10mg Lexapro.. never been on antidepressants before… and told me to start by taking half. So that’s only 5mg… and guess what happened… I went to the ER because I was convinced I was dying, I couldn’t breathe normally, and I threw up. I felt how I felt pretty much every time I ever tried E.

    I think you all would benefit from doing a DNA testing. My psychiatrist had me take one and it breaks down EVERYTHING for you.. how your body reacts to certain drugs what drugs to avoid… what drugs you may be able to take. We discovered I have a slow metabolism and drugs take a long time to effect me and when they do BAM! The effects HIT ME almost all at once, and they take longer to leave my system. I also have a few deficiencies like folic acid, etc. The test is very interesting.

    I have been on ADHD medication on and off for years, my psychiatrist says that the lexapro with the adderall could have very well been a reaction which I believe could have been a part of it but I usually always feel okay on adderall, no huge issues… but I’ve never felt the way that I do as described earlier from any other drug but drugs that release excess amounts of serotonin. Just can’t do it.

    • gherle October 5, 2016, 3:36 pm

      Same exact thing happened to me. It has been over a month since I used MDMA (first time ever), then I was having panic attacks a week after. I went to doctor and they gave me WAY too high a dosage of Lexapro and felt like I was rolling all over again. I found a new doctor who told me my serotonin was too high and I needed to level out.

      I now found I that I have slightly overactive thyroid. Don’t know if there is any correlation with using MDMA, but I still don’t feel good. I have night sweats and insomnia…don’t sleep for more than 3 solid hours. How long did it take for your serotonin to level out and for you to feel better?

    • Josh October 18, 2016, 2:32 pm

      You say DNA test.. could you be more specific? All I’m seeing are paternity tests online.

  • Dee September 19, 2016, 9:42 pm

    I have suffered serotonin syndrome three times. The last one was this past March 2016. Since my hospitalizations I have been followed closely by psychiatrist and family doc. I still do not feel well, or even feel half my previous self. I have severe joint pain, lower limb swelling, difficulty focusing, no motivation. I avoid any and every drug that could possibly cause serotonin surge. Are there long term effects to this syndrome?

  • Marie October 4, 2016, 9:50 am

    I just discovered elevated levels of serotonin. My doctor says it would be related to my thyroid medication, that it would indicate I’m hyperthyroid with too much Thyroid-medication (I have autoimmune hypothyroidism). However, I am not sure if this is the case, due to the fact I have too low rt3/ft3 ratio, which would indicate t3 hormone does not go to cellular level in adequate amounts.

    Could you advice if serotonin tells anything about thyroid medication? I’m confused and do not know whether to drop my medication (and probably end up hypothyroid again), or to add t3 medication besides natural thyroid medication to get rid of rt3-problem… Thank you already in advance!

  • Jay October 13, 2016, 11:27 am

    Hi MentalHealthDaily, I take 5-htp in the winter to help with my SAD and it works well but overtime I tend to increase the dose to 3 x 100mg tablets per day despite the on-pack advice saying 1 per day. Should I be overly concerned? And, at what point could I expect symptoms. For reference; I take brain-feed’s 5-htp because they claim to be the most premium available.

  • Jonathan Gray October 20, 2016, 9:43 pm

    I recently started on an SSRI and I developed the following symptoms: Mental confusion, sweating, shaking, severe agitation, nausea, severe bowel upsets, and this culminated in my collapsing in the street. I’m told I had a severe serotonin reaction after taking the tablets. I now manage my depression with exercise, diet and above all sleep as well as mental coping strategies.

    Sometimes I envy those who can take SSRI’s and get the benefit from them, but for myself it would seem they are a no-go. I am told it may be related to heavy usage of Ecstasy and Cocaine in my 20’s. Live and learn! I am feeling much better in myself these days though.

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