Can Serotonin Boosting Supplements Enhance Health and Improve Performance?
Serotonin, also known as 5-hydroxytryptamine (5-HT) is a neurotransmitter that is essential for health and happiness. Inadequate levels of serotonin have been linked to depression, weight gain, and insomnia. Serotonin boosting supplements were created as a way to increase levels in those lacking this neurotransmitter. Learn how these serotonin-boosting supplements may enhance health and performance.
What is Serotonin and its Function
It is secreted from enterochromaffin (EC) cells lining the GI tract. This makes up about 90% of the serotonin in the body. Platelets consist of 8% of serotonin. They absorb serotonin that is secreted from EC cells. The remaining 2% is made in the central nervous system (CNS) in the brain [R, R].
Function of Serotonin
In the gut, serotonin is responsible for regulating the intestinal movement of food through the digestive tract [R].
Excess serotonin from the gut will move into the blood and be taken up by platelets. Platelets are not able to produce new serotonin but only store it. When platelets bind to a blood clot they release serotonin. Platelet serotonin is responsible for regulating blood pressure, blood clotting, and bleeding [R].
Serotonin has also been found to have a role in immunity and wound healing [R].
Serotonin Deficiency and Low Serotonin Symptoms
Serotonin deficiency and low serotonin levels occur when there is not enough serotonin production or inactivity of EC cells.
Low serotonin symptoms manifest in both mental and physical conditions. Psychological symptoms include:
- Mood dysfunction
- Poor sleep
- Reduced appetite
- Low self-esteem
- Low libido
- Memory problems
Physical symptoms include:
- Craving carbs
- Weight gain
- Bladder issues
- Poor blood clotting
- Digestive problems
There is no clear reason why serotonin deficiency occurs but it is thought to have something to do with poor diet, chronic stress, little exercise, lack of sunlight, and aging of the brain [R].
Serotonin deficiencies can be detected with a physical exam evaluating both the physical and psychological symptoms present.
Serotonin levels can be increased with both natural serotonin boosters as well as anti-depressive medications.
SSRIs Increase Serotonin Levels
Selective serotonin reuptake inhibitors (SSRIs) are typically prescribed to improve serotonin levels. These medications will improve the efficiency of serotonin but the total levels will not change [R]. These medications are helpful but they come with side effects and may not work for everyone [R]. Luckily there are other ways to naturally increase serotonin levels.
How to Raise Serotonin Levels with Natural Serotonin Boosters
Wanting to know how to naturally increase serotonin levels was a question for those who could not benefit from SSRIs. Natural serotonin boosters are ways to naturally increase serotonin. These include diet, light therapy, exercise, and reducing stress.
Foods That Increase Serotonin
Vitamin D, omega fatty acids, B complex, zinc, magnesium, vitamin C, and vitamin E have been found to increase serotonin levels and function [R, R, R, R]. So consuming foods with these nutrients can help to improve serotonin deficiency.
Foods high in serotonin are those that contain the amino acid tryptophan. Tryptophan is an essential amino acid that needs to be obtained from the diet. Like most amino acids tryptophan helps build proteins and is needed for growth and development [R].
Tryptophan regulates the production of and maintenance of the body's proteins, muscles, enzymes, and neurotransmitters. It can also produce serotonin [R].
Tryptophan is found in the following foods:
- Egg Whites
- Sesame seeds
- Sunflower seeds
- Pumpkin seeds
Other foods that increase serotonin within the brain are those containing glucose. Glucose rich foods include fruits and vegetables [R].
Probiotics May Increase Serotonin
Serotonin production is influenced by the microbiome. Changes to gut bacteria can influence the production of serotonin in both the gut and the central nervous system.
Probiotics may increase serotonin production by reducing inflammation [R].
Strains of bacteria that show promise for improved gut-brain health include L. helveticus, B. longum, Lactobacillus, and Bifidobacterium [R].
Dosing is still being evaluated. Consuming probiotic-rich fermented foods like kefir, kimchi and sauerkraut will offer the same healthy bacteria.
Light Therapy May Increase Serotonin
Bright light therapy has been shown to possibly improve serotonin levels.
In the brain, the serotonin byproduct 5-hydroxyindoleacetic acid (5-HIAA) was increased with exposure to light and increasing light in healthy volunteers [R].
Bright light also countered the effects of tryptophan depletion in healthy women when exposed to 3000 lux of bright light [R].
Exercise May Increase Serotonin
Exercise is another natural way serotonin may be increased.
5-HIAA was higher in the cerebrospinal fluid (CSF) of patients with depression after exercising. There is some confusion as to whether the increase was due to increased serotonin production or the CSF mixing with other regions that higher 5-HIAA levels or both [R].
Studies on exercise show it is responsible for serotonin production in the brain of animals.
Neurons that produce serotonin are activated after exercise and produce more serotonin to be released in the central nervous system. [R].
Exercise has also been found to increase tryptophan which has been shown to turn into serotonin in rats [R].
In humans, serotonin production improved during and after exercise [R].
Reduce Chronic Stress for Increased Serotonin
Stress has both physical and mental effects on the body. Chronic social stress may be associated with long-term reductions in brain serotonin production.
Animals put in a stress condition had significantly lower concentrations of serotonin when compared with animals with no exposure to stress [R].
Incorporating stress-relieving activities such as exercise, meditation, and deep breathing can help to reduce stress and improve serotonin production.
Serotonin Boosting Supplements
Serotonin boosting supplements have been created as another alternative to SSRI’s. This is because serotonin-producing foods are not able to cross the blood-brain barrier and will not contribute to brain serotonin levels [R].
Compounds that have been found to increase serotonin have been manufactured as serotonin natural supplements. They include glycine, taurine, inositol, and 5-hydroxytryptophan (5-HTP).
Glycine May Increase Serotonin
Glycine is an amino acid that works as a neurotransmitter in the central nervous system [R].
Studies on the effects of serotonin by glycine are somewhat mixed. There is a positive effect of increased levels but this surge of serotonin production is short-lived.
The dose also makes a difference. Higher doses can act on serotonin receptors to improve production. Animal cells treated with glycine had a decrease in serotonin. In another experiment, a dose of 2 grams per kilogram of body weight was found to increase brain serotonin levels in rats [R, R].
In humans, glycine was highest 40 minutes after taking this supplement with a gradual decrease [R].
Further research is needed to see how glycine may improve overall serotonin levels.
Taurine May Increase Serotonin
Taurine is an amino acid that is produced by the body and is needed for the healthy function of growth, digestion, detoxification, eyes, and heart. It has been found to increase serotonin levels [R].
This is because taurine is involved in serotonin transport that moves serotonin into the CNS [R].
Taurine increased serotonin levels in rats but failed to lower inflammatory markers [R].
Inositol May Increase Serotonin
Inositol is a type of sugar that is found in the brain and other body cells. It helps neurotransmitters like serotonin send signals to keep hormone function regulated [R]
Like SSRI’s inositol is thought to activate serotonin receptors providing a similar increase in serotonin activity [R].
Inositol was reported to activate serotonin receptors in the brain to improve serotonin function [R]
Large doses of inositol reduced serotonin deficiency created by lithium use in rats [R]
The brains of rats given inositol had more serotonin activity and higher levels of serotonin for better regulation of serotonin activity [R].
5-Hydroxytryptophan (5-HTP) May Increase Serotonin
5-Hydroxytryptophan (5-HTP) is an amino acid produced by the body. It comes from the essential amino acid tryptophan. Tryptophan is then made into serotonin.
5-HTP supplements are created to enhance tryptophan production that is limited to food consumption. Foods containing tryptophan have different effects on brain serotonin.
Foods containing tryptophan have different effects on brain serotonin. Tryptophan found in foods does not cross the blood-brain barrier. This is because it is converted to serotonin in the digestive tract. Serotonin is not able to cross the blood-brain barrier so dietary tryptophan cannot increase brain serotonin [R].
Nutrients transported to the brain include all amino acids. Tryptophan is the least abundant amino acid (AA) in protein. It also needs to compete with other AA to get into the brain. Tryptophan levels will be minimal compared with other AA even after consuming a high protein food [R].
In contrast, 5-HTP easily crosses the blood-brain barrier. It does not require the presence of a transport molecule like tryptophan does [R].
As a way to increase brain serotonin levels, 5-HTP supplements were created. They come from an extract from the seeds of the African plant, Griffonia simplicifolia, and has been researched over the last 30 years due to its health benefits attributed to increasing serotonin production in the brain [R].
It is important to note 5-Hydroxytrphtopan (5-HTP) is not the same as serotonin (5-hydroxytryptamine).
5-HT vs. 5-HTP
Serotonin or 5-hydroxytryptamine (5-HT) is not the same compound as 5-hydroxytryptophan (5-HTP) found in most serotonin supplements.
5-HTP is a precursor of 5-HT. It is needed to create serotonin in the brain [R].
5-HTP has been studied for its effects on health and performance.
Benefits of Serotonin Boosting Supplements
Serotonin for Improved Immune Function
Research indicates serotonin plays a large role in immune function. Those lacking in this hormone may have poor immunity.
Serotonin receptors found within immune cells regulate inflammation and immunity in both animals and humans. Serotonin was also found to alter the release of inflammatory cytokines. Some immune cells can release serotonin to enhance it’s capabilities to other cells [R].
Specifically, there are no reports about specific research connecting 5-HTP supplements and improved immune function.
Serotonin for Improved Sleep
5-HTP was beneficial in treating insomnia and improving sleep quality.
REM sleep increased by about 20 minutes in healthy individuals taking 2 doses totaling 600 mg of 5-HTP before bed. Another smaller study had fewer increases in REM sleep using a dose of 200 mg. Doses higher tended to cause vivid dreams or nightmares [R].
Taking a 5-HTP supplement of 50 to 300 milligrams every day might improve symptoms of insomnia [R].
Serotonin for Anxiety, Depression, and Improved Mood
Depression, anxiety, and other mood disorders have been associated with poor serotonin function [R].
Serotonin has been studied for its effects on depression since the early ‘70s. Fifteen studies have examined a total of 511 individuals with different types of depression. Of these 511 people, about 56% have shown improvement while taking 5-HTP [R].
5-HTP was found work effectively as antidepressants for those with early symptoms of depression [R]
But other studies show mixed results for reducing depression symptoms. This is because serotonin deficiency is just one cause of depression. Doses of 5-HTP may not work for all of those with mood disorders [R, R].
Evidence suggests that 5-HTP and/or tryptophan are better at treating depression than a placebo, but more the quality of research done on 5-HTP and depression is poor. Longer clinical trials need to be done to know the true long term effects of 5-HTP on mood dysfunction [R].
A 2009 meta-analysis of 111 studies concluded more research needs to be done to evaluate the efficacy and safety of 5-HTP [R].
Serotonin for Weight Management
Drops in serotonin from dieting were found to result in carb cravings and binge eating in obese individuals [R].
5-HTP supplements have been found to reduce food intake and may help with weight loss. Obese women taking 5-HTP had more than a 50% reduction in carbohydrate intake when compared with a placebo [R].
Taking 300 mg of 5-HTP three times a day for 12 weeks was found to result in more significant reductions in calorie intake and weight loss in obese women when compared with the placebo regardless of dietary restrictions or structured diet [R].
Serotonin for Brain Health
Serotonin is also important for brain health and cognition. Serotonin receptors in the brain have been found responsible for learning and memory. Impairment of serotonin may lead to poor brain function [R].
Mice with impaired serotonin receptors were found to have a spatial impairment and poor memory in maze trials [R].
Serotonin receptors may play a role in the acquiring and consolidating of memory recognition.
Mice were better able to identify specific objects when these serotonin receptors were reactivated
Short and long-term memory were improved when serotonin receptors were activated [R].
No specific studies regarding improvements in brain health and 5-HTP exist so it is unknown the effects of 5-HTP on memory and learning.
Serotonin and Physical Performance
Training and intense exercise has been shown to create a stress response in the body-altering microbiota and increasing inflammation which can lead to lowering serotonin.
About 20 to 60% of athletes suffer from stress due to excessive exercise and inadequate recovery. Stress is typically higher in endurance sports such as swimming, rowing, cycling, triathlon. Long-distance runners who overtrain without taking time off have also been subject to exercise-induced stress [R].
Overtraining may result in changes in mood, appetite, cognition, performance, and sleep [R].
Diet is the key to improving gut serotonin but improvements in brain serotonin levels also need to be enhanced to prevent deficiency.
5-HTP has been shown to improve serotonin levels but there are no specific studies on how it can improve performance. Studies have tested the effects of tryptophan supplements only.
Male athletes given 300 mg of L-tryptophan had a 49.4% greater exercise time when running on a treadmill compared with those who took a placebo. Though not significant exercise fatigue was also lower in the tryptophan group [R].
Seeing the effects of tryptophan on appetite, mood, memory, and sleep it can be inferred that 5-HTP may be helpful to improve stress from overtraining. Unfortunately, there is no actual research to verify if this is true.
Risks with Serotonin Boosting Supplements
Though there is a lot of research on the benefits of 5-HTP most of it is limited to small studies.
When looking at the big picture long-term use of serotonin-boosting supplements remains unknown [R].
Tryptophan has been associated with the development of fatal blood and muscle condition. More research needs to be done to find long-term outcomes from larger clinical studies [R].
Some countries treat tryptophan as a drug because the purified form is not needed for a dietary reason and unlike food sources, this substance can pass the blood-brain barrier and increase total brain serotonin levels [R].
What to Look for in Serotonin Boosting Supplements
Since 5-HTP falls under the supplement category it is not regulated to any standards or guaranteed to work. When choosing a supplement be sure to get a quality product that is from a reliable manufacturer with third-party testing.
How to Take Serotonin Boosting Supplements
It is recommended to take 5-HTP with a meal but there are no other indications as to the best time to take serotonin-boosting supplements like 5-HTP.
It is best to follow the manufacturer’s instructions or speak with a healthcare professional.
Dosage Requirements for Serotonin Boosting Supplements
A typical dose of 5-HTP runs between 300 to 500 mg a day. They can be taken in one or two doses. Lower doses have also been shown to be effective when used in conjunction with other serotonin producers [R].
Side effects of Serotonin Boosting Supplements
Side effects have occurred in some taking 5-HTP. They include heartburn, dizziness, stomach pain, nausea, vomiting, diarrhea, drowsiness, sexual problems, and muscle problems [R].
Serotonin boosting supplements like 5-HTP may be safe when taken in doses up to 400 mg per day for one year [R].
Side effects seem to increase with long-term use. 5-HTP was found to deplete other neurotransmitters like dopamine, norepinephrine, and epinephrine. If dopamine drops too low 5-HTP will no longer work. When there are other neurotransmitters diseases are present a deficiency of dopamine, norepinephrine, and epinephrine that can worsen these conditions [R].
No toxicity reports have been noted with doses at or below 50 mg per kg of body weight [R].
Large doses of 6 to 10 grams are unsafe and caused severe stomach problems and muscle spasms [R].
The body may need to get used to taking 5-HTP. Doses of 900 mg per day were found to cause nausea in 80% of people during the first six weeks of taking 5-HTP tested. Less nausea was reported in the second six-week period [R].
When taking 5-HTP some people have developed a serious condition known as eosinophilia-myalgia syndrome (EMS). EMS causes extreme muscle tenderness and blood abnormalities [R].
Contraindications of Serotonin Boosting Supplements
Overdoing it with serotonin-boosting supplements can lead to Serotonin Syndrome. Often called tramadol serotonin syndrome since it occurs with the use of tramadol a depression medication.
Serotonin Syndrome is when the body produces excess serotonin. Elevated levels of serotonin can also occur with the combination of 5-HTP and antidepressants or any drugs that increase serotonin. Incorrect dosing or drug interactions can also cause Serotonin Syndrome.
Serotonin Syndrome was found in animals in isolation given doses of 100 to 200 mg per kilograms of body weight [R].
5-HTP should not be consumed with any neurological drug prescribed for depression or other cognitive functions unless allowed by your healthcare professional. The combination of SSRI’s and 5-HTP can be lethal [R].
5-HTP Serotonin Boosting Supplements shown to have interactions with the following drugs:
- MAO Inhibitor Drugs
- Selective Serotonin Reuptake Inhibitors (SSRIs)
There is no information on whether or not 5-HTP is safe to use when pregnant or breastfeeding so it is best to avoid this product if pregnant or breastfeeding.
Stop taking 5-HTP two weeks before surgery. Serotonin levels in the brain can become elevated leading to heart problems, shivering, and anxiety [R].
There is a lot of inconclusive research on the true benefits of 5-HTP for serotonin production. Before starting this supplement It is best to check with a healthcare professional easily if you are on medications or have any health conditions before starting this supplement [R].
Serotonin is needed for optimal function and improved performance. Though 5-HTP is a precursor to 5-HT there is still a lot we don’t know about how this supplement affects performance and overall health. If you find you have symptoms of serotonin deficiency 5-HTP may be beneficial to improve serotonin levels. It is recommended to start with a low dose to prevent serotonin syndrome. However, if you are on any medications or have pre-existing health conditions you should talk with your doctor before starting this supplement.
- Young, Simon N. 2007. “How to Increase Serotonin in the Human Brain without Drugs.” Journal of Psychiatry & Neuroscience: JPN 32 (6): 394–99. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2077351/
- Berger, Miles, John A. Gray, and Bryan L. Roth. 2009. “The Expanded Biology of Serotonin.” Annual Review of Medicine 60 (1): 355–66. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5864293/
- Yano, Jessica M., Kristie Yu, Gregory P. Donaldson, Gauri G. Shastri, Phoebe Ann, Liang Ma, Cathryn R. Nagler, Rustem F. Ismagilov, Sarkis K. Mazmanian, and Elaine Y. Hsiao. 2015. “Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis.” Cell 161 (2): 264–76.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4393509/
- Vanhoutte, P. M. 1987. “Serotonin and the Vascular Wall.” International Journal of Cardiology 14 (2): 189–203.https://pubmed.ncbi.nlm.nih.gov/3818135/
- Sadiq, Alia, Isabella Menchetti, Ahmed Shah, Marc G. Jeschke, Cassandra Belo, Wendolyn Carlos-Alcalde, Muhammad Qasim Hayat, and Saeid Amini-Nik. 2018. “5-HT1A Receptor Function Makes Wound Healing a Happier Process.” Frontiers in Pharmacology 9 (December): 1406. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6297675/
- Saldanha, D., N. Kumar, Vssr Ryali, K. Srivastava, and A. A. Pawar. 2009. “Serum Serotonin Abnormality in Depression.” Medical Journal, Armed Forces India 65 (2): 108–12.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4921409/
- Ferguson, James M. 2001. “SSRI Antidepressant Medications: Adverse Effects and Tolerability.” Primary Care Companion to the Journal of Clinical Psychiatry 3 (1): 22–27. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC181155/
- Rao, T. S. Sathyanarayana, M. R. Asha, B. N. Ramesh, and K. S. Jagannatha Rao. 2008. “Understanding Nutrition, Depression, and Mental Illnesses.” Indian Journal of Psychiatry 50 (2): 77–82. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2738337/
- Gupta, P., and J. Haria. 2014. “Relationship Between Depression and Vitamin C Status: A Study on Rural Patients From Western Uttar Pradesh in India.” https://www.semanticscholar.org/paper/e6daab1b126923cd5878df7cb88969ea9d04f3b4.
- Sabir, Marya S., Mark R. Haussler, Sanchita Mallick, Ichiro Kaneko, Daniel A. Lucas, Carol A. Haussler, G. Kerr Whitfield, and Peter W. Jurutka. 2018. “Optimal Vitamin D Spurs Serotonin: 1,25-Dihydroxyvitamin D Represses Serotonin Reuptake Transport (SERT) and Degradation (MAO-A) Gene Expression in Cultured Rat Serotonergic Neuronal Cell Lines.” Genes & Nutrition 13 (July): 19. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6042449/
- Desrumaux, Catherine M., Marine Mansuy, Stéphanie Lemaire, Justine Przybilski, Naig Le Guern, Laurent Givalois, and Laurent Lagrost. 2018. “Brain Vitamin E Deficiency During Development Is Associated With Increased Glutamate Levels and Anxiety in Adult Mice.” Frontiers in Behavioral Neuroscience 12 (December): 310.https://www.frontiersin.org/articles/10.3389/fnbeh.2018.00310/full
- “Tryptophan.” n.d. https://medlineplus.gov/ency/article/002332.htm
- Pereira, Nádia, Maria Fernanda Naufel, Eliane Beraldi Ribeiro, Sergio Tufik, and Helena Hachul. 2020. “Influence of Dietary Sources of Melatonin on Sleep Quality: A Review.” Journal of Food Science 85 (1): 5–13. https://onlinelibrary.wiley.com/doi/full/10.1111/1750-3841.14952
- Wallace, Caroline J. K., and Roumen Milev. 2017. “The Effects of Probiotics on Depressive Symptoms in Humans: A Systematic Review.” Annals of General Psychiatry 16 (February): 14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5319175/
- Lambert, G. W., C. Reid, D. M. Kaye, G. L. Jennings, and M. D. Esler. 2002. “Effect of Sunlight and Season on Serotonin Turnover in the Brain.” The Lancet 360 (9348): 1840–42. https://pubmed.ncbi.nlm.nih.gov/12480364/
- Rot, Marije aan het, Chawki Benkelfat, Diane B. Boivin, and Simon N. Young. 2008. “Bright Light Exposure during Acute Tryptophan Depletion Prevents a Lowering of Mood in Mildly Seasonal Women.” European Neuropsychopharmacology: The Journal of the European College of Neuropsychopharmacology 18 (1): 14–23. https://pubmed.ncbi.nlm.nih.gov/17582745/
- Ferraro, J. S., and R. W. Steger. 1990. “Diurnal Variations in Brain Serotonin Are Driven by the Photic Cycle and Are Not Circadian in Nature.” Brain Research 512 (1): 121–24. https://pubmed.ncbi.nlm.nih.gov/2337799/
- Cagampang, F. R., S. Yamazaki, Y. Otori, and S. I. Inouye. 1993. “Serotonin in the Raphe Nuclei: Regulation by Light and an Endogenous Pacemaker.” Neuroreport 5 (1): 49–52. https://pubmed.ncbi.nlm.nih.gov/8280860/
- Chaouloff, F., J. L. Elghozi, Y. Guezennec, and D. Laude. 1985. “Effects of Conditioned Running on Plasma, Liver and Brain Tryptophan and on Brain 5-Hydroxytryptamine Metabolism of the Rat.” British Journal of Pharmacology 86 (1): 33–41. https://pubmed.ncbi.nlm.nih.gov/2413941/
- Wilson, W. M., and C. A. Marsden. 1996. “In Vivo Measurement of Extracellular Serotonin in the Ventral Hippocampus during Treadmill Running.” Behavioural Pharmacology 7 (1): 101–4. https://pubmed.ncbi.nlm.nih.gov/11224400/
- Gomez-Merino, D., F. Béquet, M. Berthelot, M. Chennaoui, and C. Y. Guezennec. 2001. “Site-Dependent Effects of an Acute Intensive Exercise on Extracellular 5-HT and 5-HIAA Levels in Rat Brain.” Neuroscience Letters 301 (2): 143–46. https://www.ncbi.nlm.nih.gov/pubmed/11248443
- Meeusen, R., and K. De Meirleir. 1995. “Exercise and Brain Neurotransmission.” Sports Medicine 20 (3): 160–88.https://pubmed.ncbi.nlm.nih.gov/8571000/
- Post, R. M., and F. K. Goodwin. 1973. “Simulated Behavior States: An Approach to Specificity in Psychobiological Research.” Biological Psychiatry 7 (3): 237–54. https://pubmed.ncbi.nlm.nih.gov/4357567/
- Rueter, L. E., and B. L. Jacobs. 1996. “A Microdialysis Examination of Serotonin Release in the Rat Forebrain Induced by Behavioral/environmental Manipulations.” Brain Research 739 (1-2): 57–69.https://pubmed.ncbi.nlm.nih.gov/8955925/
- Fontenot, M. B., J. R. Kaplan, S. B. Manuck, V. Arango, and J. J. Mann. 1995. “Long-Term Effects of Chronic Social Stress on Serotonergic Indices in the Prefrontal Cortex of Adult Male Cynomolgus Macaques.” Brain Research 705 (1-2): 105–8. https://pubmed.ncbi.nlm.nih.gov/8821740/
- Bannai, Makoto, Nobuhiro Kawai, Kenji Nagao, Sayako Nakano, Daisuke Matsuzawa, and Eiji Shimizu. 2011. “Oral Administration of Glycine Increases Extracellular Serotonin but Not Dopamine in the Prefrontal Cortex of Rats.” Psychiatry and Clinical Neurosciences 65 (2): 142–49.https://pubmed.ncbi.nlm.nih.gov/21414089/
- Becquet, D., M. Héry, P. Deprez, M. Faudon, M. P. Fache, P. Giraud, and F. Héry. 1993. “N-Methyl-D-Aspartic Acid/glycine Interactions on the Control of 5-Hydroxytryptamine Release in Raphe Primary Cultures.” Journal of Neurochemistry 61 (5): 1692–97.https://pubmed.ncbi.nlm.nih.gov/7901329/
- Becquet, D., M. Hery, A. M. Francois-Bellan, P. Giraud, P. Deprez, M. Faudon, M. P. Fache, and F. Hery. 1993. “Glutamate, GABA, Glycine and Taurine Modulate Serotonin Synthesis and Release in Rostral and Caudal Rhombencephalic Raphe Cells in Primary Cultures.” Neurochemistry International 23 (3): 269–83.https://pubmed.ncbi.nlm.nih.gov/7693110/
- Gannon, Mary C., Jennifer A. Nuttall, and Frank Q. Nuttall. 2002. “The Metabolic Response to Ingested Glycine.” The American Journal of Clinical Nutrition 76 (6): 1302–7.https://pubmed.ncbi.nlm.nih.gov/12450897/
- Birdsall, T. C. 1998. “Therapeutic Applications of Taurine.” Alternative Medicine Review: A Journal of Clinical Therapeutic 3 (2): 128–36. https://pubmed.ncbi.nlm.nih.gov/9577248/
- Ripps, Harris, and Wen Shen. 2012. “Review: Taurine: A ‘Very Essential’ Amino Acid.” Molecular Vision 18 (November): 2673–86.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3501277/
- Wu, Gao-Feng, Shuang Ren, Ri-Yi Tang, Chang Xu, Jia-Qi Zhou, Shu-Mei Lin, Ying Feng, Qun-Hui Yang, Jian-Min Hu, and Jian-Cheng Yang. 2017. “Antidepressant Effect of Taurine in Chronic Unpredictable Mild Stress-Induced Depressive Rats.” Scientific Reports 7 (1): 4989.https://pubmed.ncbi.nlm.nih.gov/28694433/
- Parthasarathy, Latha K., Ratnam S. Seelan, Carmelita Tobias, Manuel F. Casanova, and Ranga N. Parthasarathy. 2006. “Mammalian Inositol 3-Phosphate Synthase: Its Role in the Biosynthesis of Brain Inositol and Its Clinical Use as a Psychoactive Agent.” Sub-Cellular Biochemistry 39: 293–314. https://pubmed.ncbi.nlm.nih.gov/17121280/
- Fux, Mendel, Jonathan Benjamin, and R. H. Belmaker. 1999. “Inositol versus Placebo Augmentation of Serotonin Reuptake Inhibitors in the Treatment of Obsessive-Compulsive Disorder: A Double-Blind Cross-over Study.” The International Journal of Neuropsychopharmacology / Official Scientific Journal of the Collegium Internationale Neuropsychopharmacologicum 2 (3): 193–95. https://pubmed.ncbi.nlm.nih.gov/11281989/
- Levine, J. 1997. “Controlled Trials of Inositol in Psychiatry.” European Neuropsychopharmacology: The Journal of the European College of Neuropsychopharmacology 7 (2): 147–55. https://pubmed.ncbi.nlm.nih.gov/9169302/
- Kofman, O., and U. Levin. 1995. “Myo-Inositol Attenuates the Enhancement of the Serotonin Syndrome by Lithium.” Psychopharmacology 118 (2): 213–18.https://pubmed.ncbi.nlm.nih.gov/7617810/
- Rahman, S., and R. S. Neuman. 1993. “Myo-Inositol Reduces Serotonin (5-HT2) Receptor Induced Homologous and Heterologous Desensitization.” Brain Research 631 (2): 349–51. https://pubmed.ncbi.nlm.nih.gov/8131066/
- Birdsall, T. C. 1998. “5-Hydroxytryptophan: A Clinically-Effective Serotonin Precursor.” Alternative Medicine Review: A Journal of Clinical Therapeutic 3 (4): 271–80. https://pubmed.ncbi.nlm.nih.gov/9727088/
- Hinz, Marty, Alvin Stein, and Thomas Uncini. 2012. “5-HTP Efficacy and Contraindications.” Neuropsychiatric Disease and Treatment 8 (July): 323–28. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3415362/
- Roumier, Anne, Catherine Béchade, and Luc Maroteaux. 2019. “Chapter 10 - Serotonin and the Immune System.” In Serotonin, edited by Paul M. Pilowsky, 181–96. Boston: Academic Press.https://www.sciencedirect.com/science/article/pii/B9780128000502000103
- Portas, C. M., B. Bjorvatn, and R. Ursin. 2000. “Serotonin and the Sleep/wake Cycle: Special Emphasis on Microdialysis Studies.” Progress in Neurobiology 60 (1): 13–35. https://pubmed.ncbi.nlm.nih.gov/10622375/
- Aulinas, Anna. 2019. “Physiology of the Pineal Gland and Melatonin.” In Endotext, edited by Kenneth R. Feingold, Bradley Anawalt, Alison Boyce, George Chrousos, Kathleen Dungan, Ashley Grossman, Jerome M. Hershman, et al. South Dartmouth (MA): MDText.com, Inc. https://www.ncbi.nlm.nih.gov/books/NBK550972/
- Jangid, Purushottam, Prerna Malik, Priti Singh, Minakshi Sharma, and Anil Kumar D. Gulia. 2013. “Comparative Study of Efficacy of L-5-Hydroxytryptophan and Fluoxetine in Patients Presenting with First Depressive Episode.” Asian Journal of Psychiatry 6 (1): 29–34. https://pubmed.ncbi.nlm.nih.gov/23380314/
- Shaw, K., J. Turner, and C. Del Mar. 2002. “Tryptophan and 5-Hydroxytryptophan for Depression.” Cochrane Database of Systematic Reviews , no. 1: CD003198. https://pubmed.ncbi.nlm.nih.gov/11869656/
- Yano, Jessica M., Kristie Yu, Gregory P. Donaldson, Gauri G. Shastri, Phoebe Ann, Liang Ma, Cathryn R. Nagler, Rustem F. Ismagilov, Sarkis K. Mazmanian, and Elaine Y. Hsiao. 2015. “Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis.” Cell 161 (2): 264–76. https://pubmed.ncbi.nlm.nih.gov/130678/
- Goudie, A. J., E. W. Thornton, and T. J. Wheeler. 1976. “Effects of Lilly 110140, a Specific Inhibitor of 5-Hydroxytryptamine Uptake, on Food Intake and on 5-Hydroxytryptophan-Induced Anorexia. Evidence for Serotoninergic Inhibition of Feeding.” The Journal of Pharmacy and Pharmacology 28 (4): 318–20. https://pubmed.ncbi.nlm.nih.gov/6727/
- Samanin, R., T. Mennini, and S. Garattini. 1980. “Evidence That It Is Possible to Cause Anorexia by Increasing Release And/or Directly Stimulating Postsynaptic Serotonin Receptors in the Brain.” Progress in Neuro-Psychopharmacology 4 (4-5): 363–69. https://pubmed.ncbi.nlm.nih.gov/7220662/
- Heisler, Lora K., Erin E. Jobst, Gregory M. Sutton, Ligang Zhou, Erzsebet Borok, Zoe Thornton-Jones, Hong Yan Liu, et al. 2006. “Serotonin Reciprocally Regulates Melanocortin Neurons to Modulate Food Intake.” Neuron 51 (2): 239–49. https://pubmed.ncbi.nlm.nih.gov/16846858/
- Wurtman, R. J., and J. J. Wurtman. 1995. “Brain Serotonin, Carbohydrate-Craving, Obesity and Depression.” Obesity Research 3 Suppl 4 (November): 477S – 480S. https://pubmed.ncbi.nlm.nih.gov/8697046/
- Nikiforuk, Agnieszka. 2015. “Targeting the Serotonin 5-HT7 Receptor in the Search for Treatments for CNS Disorders: Rationale and Progress to Date.” CNS Drugs 29 (4): 265–75. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4555343/
- Sarkisyan, Gor, and Peter B. Hedlund. 2009. “The 5-HT7 Receptor Is Involved in Allocentric Spatial Memory Information Processing.” Behavioural Brain Research 202 (1): 26–31. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684518/
- MacKinnon, L. T. 2000. “Special Feature for the Olympics: Effects of Exercise on the Immune System: Overtraining Effects on Immunity and Performance in Athletes.” Immunology and Cell Biology 78 (5): 502–9. https://www.ncbi.nlm.nih.gov/pubmed/11050533/
- Clark, Allison, and Núria Mach. 2016. “Exercise-Induced Stress Behavior, Gut-Microbiota-Brain Axis and Diet: A Systematic Review for Athletes.” Journal of the International Society of Sports Nutrition 13 (November): 43. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5121944/
- Segura, R., and J. L. Ventura. 1988. “Effect of L-Tryptophan Supplementation on Exercise Performance.” International Journal of Sports Medicine 9 (5): 301–5. https://pubmed.ncbi.nlm.nih.gov/3246461/
- “5-Htp: Uses, Side Effects, Interactions, Dosage, and Warning.” n.d. Accessed September 29, 2020. https://www.webmd.com/vitamins/ai/ingredientmono-794/5-htp
- Turner, Erick H., Jennifer M. Loftis, and Aaron D. Blackwell. 2006. “Serotonin a La Carte: Supplementation with the Serotonin Precursor 5-Hydroxytryptophan.” Pharmacology & Therapeutics 109 (3): 325–38. https://pubmed.ncbi.nlm.nih.gov/16023217/
- Nardini, M., R. De Stefano, M. Iannuccelli, R. Borghesi, and N. Battistini. 1983. “Treatment of Depression with L-5-Hydroxytryptophan Combined with Chlorimipramine, a Double-Blind Study.” International Journal of Clinical Pharmacology Research 3 (4): 239–50. https://pubmed.ncbi.nlm.nih.gov/6381336/
- Nicolodi, M., and F. Sicuteri. 1996. “Fibromyalgia and Migraine, Two Faces of the Same Mechanism. Serotonin as the Common Clue for Pathogenesis and Therapy.” Advances in Experimental Medicine and Biology 398: 373–79. https://pubmed.ncbi.nlm.nih.gov/8906292/
- Aliño, J. J., J. L. Gutierrez, and M. L. Iglesias. 1976. “5-Hydroxytryptophan (5-HTP) and a MAOI (nialamide) in the Treatment of Depressions. A Double-Blind Controlled Study.” International Pharmacopsychiatry 11 (1): 8–15. https://pubmed.ncbi.nlm.nih.gov/770365/
- Kline, N., and W. Sacks. 1980. “Treatment of Depression with an Mao Inhibitor Followed by 5-HTP--an Unfinished Research Project.” Acta Psychiatrica Scandinavica. Supplementum 280: 233–41. https://pubmed.ncbi.nlm.nih.gov/6996430/
- “Eosinophilia-Myalgia Syndrome - NORD (National Organization for Rare Disorders).” n.d. Accessed September 29, 2020. https://rarediseases.org/rare-diseases/eosinophilia-myalgia-syndrome/
- Centers for Disease Control (CDC). 1990. “Update: Analysis of L-Tryptophan for the Etiology of Eosinophilia-Myalgia Syndrome.” MMWR. Morbidity and Mortality Weekly Report 39 (43): 789–90.https://www.cdc.gov/mmwr/preview/mmwrhtml/00001739.htm
- Frank, Kurtis, Kamal Patel, Gregory Lopez, and Bill Willis. 2019. “5-HTP Research Analysis,” February. https://examine.com/supplements/5-htp/#how-to-take