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.