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  • Promotes a healthy mood
  • Promotes restful sleep
  • Supports healthy cognitive function


This essential amino acid supplement is one of several amino acids that are used for protein synthesis and cannot be produced by the human body. As a result, all L-Tryptophan must be consumed in the diet. It has essential roles in the synthesis of serotonin and melatonin, as well as in several other important biochemical pathways in the body. As a supplement, it is best known for its effects on mood, sleep, and cognition. Larger servings may reduce appetite.


This supplement is best taken at a serving size of 500 – 1000mg, once to twice daily. It is not recommended to exceed the serving size, even though side effects are reportedly mild and rare. Larger servings may cause nausea, heartburn, upset stomach, gas, headaches, dry mouth, and drowsiness. Consult with a physician before using this supplement if you have any underlying medical conditions or are using medication. 


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  • L-Tryptophan is an essential amino acid found in foods that are rich in protein and has important roles in protein synthesis and a variety of biochemical systems in the body.


  • Effective at supporting a healthy mood, promoting restful sleep, supporting healthy cognition, and suppressing appetite.


  • Recommended serving size for this supplement is 500 – 1000mg, taken once to twice daily.


  • Not recommended to exceed serving size. Side effects may include nausea, heartburn, upset stomach, gas, headaches, dry mouth, and drowsiness.

L-Tryptophan reviews





L-Tryptophan is an essential nutrient and amino acid that is used in the biosynthesis of proteins. It was first discovered in the early 20th century after being isolated from casein protein by Hopkins and Cole.[1] It cannot be synthesized by the human body but is essential for proper physiological function and protein synthesis. Some common food sources of this nutrient include bananas, oats, prunes, milk, cheese, bread, peanuts, and chocolate.[2] Being an amino acid, this nutrient plays a vital role in structural processes of our bodies – it is one of the 22 building blocks of all proteins. Its role as a precursor to serotonin, melatonin and niacin are important when examining its effects as an effective dietary supplement.[3]


When taken as a supplement, L-Tryptophan is known to be effective in promoting a number of great benefits. For example, it can be used to help support healthy cognitive performance, to promote feelings of relaxation, to help with healthy, restful sleep and stress reduction, and to improve exercise performance. There is also evidence that this interesting nutrient has a strong functionality in the gut-brain axis.[4]


In terms of its importance for proper functionality of physiological processes in the human body, Richard et al. (2009) outlined its uses, as summarised below:

  1. Protein Synthesis – This amino acid tends to be found in the lowest concentrations of all amino acids in the body. Therefore, it often acts as the rate-limiting factor in protein synthesis. Proteins are used as enzymes, for immune function, to produce hormones, in energy production and, of course, for the building of muscles.

  2. Kynurenine synthesis – around 90% of the Tryptophan that is not used in protein synthesis is metabolised to form kynurenine, a key component of several biochemical pathways and essential for the synthesis of niacin (vitamin B3). Kynurenic and quinolinic acids (produced in this pathway) are also essential for modulating excitatory neurotransmitters in the brain and supporting a healthy nervous system.

  3. Serotonin synthesis – while only a small percentage of dietary Tryptophan is used in serotonin synthesis, this function is of great interest to researchers because of its importance in brain function. Serotonin is a neurotransmitter and neuromodulator and has important roles to play in maintaining psychological processes.
  4. Tryptamine synthesis – the metabolism of this amino acid produces small amounts of tryptamine, which is an important modulator of serotonin’s functions in the gut and brain.

  5. Melatonin synthesis – this hormone is produced in the tryptophan/serotonin pathway and is secreted by the pineal gland in response to changes in the light/dark cycle. It is essentially responsible for controlling the circadian rhythm and has a vital role in maintaining healthy sleep.

  6. NAD/NADP synthesis – this vital amino acid has an important role to play in the synthesis of NAD and NADP, which are vital for electron transfer reactions in all living cells. [5]

From the above information, we can easily see that this essential amino acid has a variety of important functions in the body.


L-Tryptophan Effects / Benefits


1.     Helps to Support a Healthy Mood


L-Tryptophan is a biochemical precursor to both serotonin and melatonin. Supplementing with this amino acid has been shown to increase serum serotonin and melatonin levels, in animal studies.[6] This is important for its benefits relating to support for a healthy mood.

Serotonin has long been associated with increased mood and happiness.[7] Acute Tryptophan depletion (ATD) is associated with irritability and low general mood.[8] Low serotonin has been shown to contribute to low mood and mood swings. Mood is dependent on many factors, including the balance of hormones in the brain, as well as stress, diet, exercise, environmental factors, and susceptibility to depression and anxiety.

A recent review on serotonin studies found that while low serotonin levels may not directly cause low moods, higher serotonin levels were associated with better social interactions (less aggressive and more agreeable) and an improvement in mood.[9] Therefore, while the evidence is not yet conclusive that serotonin directly increases mood in all people; it can be stated that serotonin does increase positive social behaviour, which certainly contributes to a better mood.

This is important because this supplement directly increases serum serotonin levels and therefore contributes to more agreeable social behaviour and interactions, which helps to support a better mood.[10] Furthermore, mood and sleep are known to be intricately connected. Since this supplement may help to support restful sleep (see below), this is another contributing factor to its beneficial effects on mood.


2.     Promotion of Healthy Sleep


Melatonin is a product of the biochemical pathway which produces serotonin from Tryptophan. Although this only represents a very small fraction of dietary Tryptophan, its role in maintaining healthy sleep is nevertheless of great importance. Melatonin is the brain’s natural sleep hormone. It is produced by the pineal gland in response to changes in environmental light and helps to regulate the circadian rhythm. Specifically, melatonin acts as a signalling hormone to ‘tell’ various parts of the body to get ready for sleep.[11]

Studies show that this dietary supplement is effective at increasing melatonin levels, and this is a logical conclusion based on its being a precursor to serotonin. Multiple studies have shown the efficiency of L-Tryptophan supplements for promoting healthy, restful sleep. It appears to be efficient in lowering the sleep latency time (length of time from full wakefulness to sleep) in younger insomniacs from the first night of dosage. This supplement has also been shown to help improve sleep over a longer period of time and when used in cycles, known as “interval therapy”.[12]


3.     Helps to Support Healthy Cognitive Functions


It is well known that this supplement helps to improve serotonin levels and, therefore, helps to support a healthy mood. What is less understood about it is that serotonin is also of great importance for supporting healthy cognitive function. In fact, serotonin receptors are found in all the brain regions that are involved in learning and memory. These include the cortex, amygdala, and hippocampus.[13] 

Furthermore, many recently developed chemical compounds for improving cognition (sometimes called Nootropics) target serotonin receptors like the 5-HT2A/2C or 5-HT4 receptor agonists and 5-HT1A or 5HT3 and 5-HT1B receptor antagonists. It is still not fully understood whether serotonin helps to modulate cognitive function through specific effects on learning, memory or executive functions in the brain. However, studies using experimentally reduced serotonin levels have elucidated some of the roles of this neurotransmitter on learning capacity.[14]


4.     Helps to Support a Healthy Body


As we’ve seen in the background to this fascinating amino acid supplement, it has several essential roles in maintaining a healthy body. Taking this supplement helps to support protein synthesis, which is essential for a healthy body. It is also metabolised into kynurenine, which is used for the synthesis of kynurenic and quinolinic acids. These important compounds are used to modulate the effects of excitatory and inhibitory neurotransmitters in the brain, and to help maintain a healthy chemical balance.[15] This essential amino acid is also involved in the synthesis of tryptamine, which helps to modulate the effects of serotonin in the brain and the gut.


5.     May Help with Appetite Suppression


Many supplements and chemicals that increase levels of serotonin, or inhibit the breakdown of naturally released serotonin are considered effective at lowering appetite. Research has found that higher serum serotonin levels specifically correspond to reduced cravings for carbohydrates over other food types.

A recent study on L-Tryptophan supplementation in patients suffering from obesity and eating disorders found a clear correlation between this supplement and appetite suppression. The study was conducted on 20 obese patients. 10 were given a variety of serving sizes (1, 2 and 3g) before a plated meal was served (group 1). The other 10 (group 2) were given lactose as a placebo.

The mean ± SD total calorie intakes were: group I 1188 ± 94 (1 g); 1031 ± 93 (2 g: p < 0.05) and 1016 ± 85 (3g: p<0.05); group II: 1294 ± 62. There was a progressive decrease in carbohydrate consumption (expressed as available monosaccharide) in function of the tryptophan does: placebo 131 ± 8 g; one g tryptophan 123 ± 9; two g 114 ± 13; three g 107 ± 10. Protein consumption was less affected.” (Cavaliere and Medeiros-Neto, 2014)

These results show clearly show a significant, dose-dependent decrease in food consumption (specifically carbohydrates) associated with this supplement.[16]



L-Tryptophan Recommended Usage


Studies have indicated that this supplement is effective, even at serving sizes as low as 250mg.[17] Most studies recommend a serving size of 500 – 1000 mg, taken once to twice daily. For appetite suppressive benefits, a larger serving size may be useful. Exceeding the serving suggestion may not improve the effects of this supplement.


L-Tryptophan Side Effects & Warnings


WebMD suggests that possible side effects of L-Tryptophan supplements may include heartburn, stomach pain, dizziness, dry mouth, gas and headache.[18] Taking excessively large serving sizes may cause nausea, drowsiness, and loss of libido. Do not exceed the recommended serving size. If you have any underlying medical conditions or are using any medication, please consult with your doctor before using this supplement.



In summary, this supplement is an essential amino acid that is used in protein synthesis and cannot be manufactured by the human body. There are many food sources that are rich in Tryptophan. When taken as a supplement, it is best known for its effects on mood. This supplement helps to promote a healthy mood through its effects on serotonin. It has several secondary benefits like helping to improve sleep quality, supporting healthy cognitive function, and suppressing appetite (at larger serving sizes).

The recommended serving size for this supplement is 500 – 1000mg, taken once to twice per day. Since it is an essential nutrient, it is relatively free from side effects when used at the recommended serving size. At larger servings, it may cause nausea, drowsiness, headaches, dry mouth, and an upset stomach. Talk to your doctor before using this supplement if you have any underlying medical conditions or are taking any medication.



Medical Disclaimer: 

Not intended to treat, diagnose, or cure any disease or ailment. Please read and fully understand potential adverse effects before using this product. These statements have not been reviewed by the FDA and are not written by a medical professional. Please consult your doctor before using any supplements, especially if you have any medical conditions.



[1] Hopkins FG, Cole SW. “A contribution to the chemistry of proteids: Part I. A preliminary study of a hitherto undescribed product of tryptic digestion.” J Physiol. 1901 Dec 23; 27(4-5):418-28.

[2] “Food sources of Tryptophan”, SELF nutrition data, available online from [Accessed May 14, 2018]   

[3] “Tryptophan” MedlinePlus, Online Medical Encyclopaedia, available online from [Accessed May 14, 2018]


[4] Kałużna-Czaplińska J, Gątarek P, Chirumbolo S, Chartrand MS, Bjørklund G. “How important is tryptophan in human health?Crit Rev Food Sci Nutr. 2017 Aug 11:1-17.

[5] Richard DM, Dawes MA, Mathias CW, Acheson A, Hill-Kapturczak N, Dougherty DM. “L-Tryptophan: Basic Metabolic Functions, Behavioral Research and Therapeutic Indications.” International Journal of Tryptophan Research : IJTR. 2009;2:45-60.

[6] “Effect of orally administered L-tryptophan on serotonin, melatonin, and the innate immune response in the rat” Esteban S,Nicolaus C, Garmundi A, Rial RV, Rodríguez AB, Ortega E, Ibars CB, Mol Cell Biochem. 2004 Dec;267(1-2):39-46.


[7] Strasser B, Gostner JM, Fuchs D. “Mood, food, and cognition: role of tryptophan and serotonin.” Curr Opin Clin Nutr Metab Care. 2016 Jan;19(1):55-61.

[8] Merens W, Willem Van der Does AJ, Spinhoven P. “The effects of serotonin manipulations on emotional information processing and mood.” J Affect Disord. 2007 Nov;103(1-3):43-62. Epub 2007 Mar 23.

[9] Young SN, Leyton M. “The role of serotonin in human mood and social interaction. Insight from altered tryptophan levels.” Pharmacol Biochem Behav. 2002 Apr;71(4):857-65.

[10]  “The effect of raising and lowering tryptophan levels on human mood and social behaviour”, Simon N. Young, Philosophical Transactions B, February 2013 Volume: 370 Issue: 1661

[11] Ferracioli-Oda E, Qawasmi A, Bloch MH. “Meta-analysis: melatonin for the treatment of primary sleep disorders.” PLoS One. 2013 May 17;8(5):e63773.

[12]  “Evaluation of L-tryptophan for treatment of insomnia: a review” Schneider-Helmert D, Spinweber CL, Psychopharmacology (Berl). 1986;89(1):1-7

[13] Meneses A. “5-HT system and cognition.” Neurosci. Biobehav. R. 1999;23:1111–1125

[14] Jenkins TA, Nguyen JCD, Polglaze KE, Bertrand PP. “Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis.Nutrients. 2016;8(1):56.

[15] Stone TW. “Neuropharmacology of quinolinic and kynurenic acids.” Pharmacol Rev. 1993 Sep;45(3):309-79.

[16] Cavaliere H, Medeiros-Neto G. “The anorectic effect of increasing doses of L-tryptophan in obese patients” Eat Weight Disord. 1997 Dec;2(4):211-5.

[17] Hartmann E, Spinweber CL “Sleep induced by L-tryptophan. Effect of dosages within the normal dietary intake.”, J Nerv Ment Dis. 1979 Aug;167(8):497-9.

[18] “L-Tryptophan”, available online from [Accessed May 14, 2018]