Symptom's Associated with Abnormal Serotonin Levels

From brainmatrix

Note of Relevance for Functional Medicine: The essential amino acid tryptophan that is found in several foods is the sole precursor to serotonin in the nervous system.1 Tryptophan is found in:1,2

  • Meats
  • Dairy foods
  • Fruits
  • Seeds

The availability of tryptophan is increased with high-glycemic index and high-glycemic load foods and meals.3

Affective Disorders and Mood[edit]

(-) Depression. Serotonin has long been implicated in depression.4–8 Research into the connection between serotonin and depression suggests that serotonin dysfunction may cause depression in certain circumstances and reduced serotonin activity may make it difficult to recover from depression. Serotonin is thought to contribute to negative thinking patterns. Serotonin forms the basis of several depression treatments, including with selective serotonin reuptake inhibitors (SSRI).5, 6,9

(+/-) Anxiety/Panic. Serotonin activity is thought to play a role in panic disorder, and both too much and too little serotonin have been implicated in panic and different forms of anxiety.10–12 The relationship between anxiety and serotonin may in part occur because of the role of serotonin in the stress response.13

(+/-) Mood. Higher levels of serotonin are associated with improved mood, whereas serotonin dysfunction has been linked to suicidal ideation.5,9 Research on menopausal women has shown that changes in serotonin function are implicated in mood alterations in those undergoing estrogen treatment.14


*Serotonin’s role in cognition may involve its interaction with dopamine.15

(+/-) Cognitive Performance. Reduced serotonin neurotransmission appears to have a negative impact on cognitive functions, and normalizing serotonin levels may be beneficial for restoring cognitive performance, particularly in the context of neuropsychiatric disorders.16 However, there are also data that suggest that during the acute phase of SSRI treatment, cognitive dysfunction may occur.17

Serotonin has been implicated in the cognitive symptoms of Alzheimer’s disease (AD), but the specific role that serotonin stimulation could play in influencing these symptoms has not been sufficiently studied.18

(+/-) Learning. Research shows that administering certain serotonin agonists and certain serotonin antagonists can facilitate learning in contexts where cognitive demand is high.1

(-) Memory. Several studies suggest that low extracellular serotonin levels are associated with impairments in the consolidation of memories.19


(+) Impulsivity. Serotonin may be associated with preference for immediate reward and increased impulsivity.209

(+/-) Eating Behavior. Serotonin is implicated in feelings of satiety, and serotonin dysfunction can therefore lead to increases or decreases in appetite that are associated with eating disorders or obesity.9,13,21

(-) Social Adaptation. Serotonin is heavily implicated in social and moral behavior.22 The use of serotonin and norepinephrine reuptake inhibitors (SNRI) in patients with depression has been linked to improvements in social adaptation.9

(+/-) Aggression. Changes in serotonin are linked to aggression, though the specific mechanisms by which serotonin may contribute to aggressive behavior is not entirely understood.12 However, serotonin dysfunction is implicated in feelings of frustration and agitation, which may contribute to aggressive behavior.9

(+/-) Sexual Behavior. Decreased libido has been linked to serotonin dysfunction.9 However, sexual dysfunction is also a common unwanted side effect of SSRIs.12

Physical Symptoms[edit]

*Many physical symptoms of serotonin dysregulation occur due to its role as a hormone, neuromodulator rather than as a neurotransmitter (see relevant hormone document for details).

(+/-) Heart Rate. Serotonin plays a role in the communication between the brain and the heart in those with panic disorder and in those on serotonin reuptake inhibitors. Changes in serotonin levels may therefore be associated with changes in heart rate.11

(+/-) Pain. Serotonin is known to regulate pain, which may occur in part due to interactions with other hormones.16,23,24 Specifically, it may enhance pain sensation through its role as an inflammatory mediator.25 Low central serotonin levels have been implicated in migraine headaches, and triptans, agonists of certain classes of serotonin receptors are the first-line of acute treatment for the disorder.

(+/-) Sleep. Serotonin interacts with the brain systems involved in sleep and waking.26,27 Changes in serotonin levels can have differential effects on wakefulness and fatigue.

(-) Premenstrual syndrome. Serotonin is implicated in premenstrual syndrome (PMS), and serotonin reuptake inhibitors that increase serotonin levels have been shown to improve symptoms.28,29

(+/-) Body temperature. Serotonin helps to regulate body temperature, so changes in body temperature or body temperature regulation may occur with serotonin dysfunction.13


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2. Friedman M, Levin CE. Nutritional and medicinal aspects of D-amino acids. Amino Acids. 2012;42(5):1553-1582. doi:10.1007/S00726-011-0915-1

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23. Paredes S, Cantillo S, Candido KD, Knezevic NN. An Association of Serotonin with Pain Disorders and Its Modulation by Estrogens. Int J Mol Sci. 2019;20(22). doi:10.3390/IJMS20225729

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25. Wang X, Li WG, Yu Y, et al. Serotonin facilitates peripheral pain sensitivity in a manner that depends on the nonproton ligand sensing domain of ASIC3 channel. J Neurosci. 2013;33(10):4265-4279. doi:10.1523/JNEUROSCI.3376-12.2013

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