L-Tryptophan Common Name


Top Benefits of L-Tryptophan

  • Supports cell energy generation*
  • Supports healthy aging*
  • Supports healthy sleep and body clock function*
  • Supports prosocial behaviors*

What is L-Tryptophan?

L-Tryptophan is an essential amino acid. The body cannot synthesize it: it must be obtained from the diet. It functions as a metabolic precursor (i.e., substrate) for the synthesis of nicotinamide adenine dinucleotide (NAD), an important coenzyme found in all living cells—NAD is used for mitochondrial energy production and activation of the important sirtuin healthspan pathways. NAD can be made by any molecule which contains a niacin or nicotinamide (vitamin B3) molecule. L-Tryptophan is unique because it’s the only other way to build NAD that doesn’t start from vitamin B3. L-Tryptophan is also the precursor for the synthesis of the neurotransmitter serotonin and the neurohormone melatonin, which regulates sleep-wake cycles and nighttime body clock functions. In addition to these three main molecules, L-tryptophan is involved in making many other important intermediate molecules. Giving extra L-tryptophan allows the body to use it where it is needed most … at that time and over the next 12-16 hours. In general, giving extra L-tryptophan with breakfast supports both daytime mood (presumably via supporting serotonin function) and nightly sleep (presumably via supporting melatonin function). Giving some extra L-tryptophan also helps support body clock, orienting many of it’s daytime functions earlier in the day. L-tryptophan supplementation may support prosocial behaviors. Low-to-modest doses of L-tryptophan prior to bed may support healthier sleep cycles.

Neurohacker’s L-Tryptophan Sourcing

L-Tryptophan is used as a precursor (i.e., substrate) by the body to make NAD, serotonin, and melatonin. Our main reason for including it in a formulation would be to support biosynthesis of one or more of these important molecules.

In general, L-tryptophan is additive with other strategies for making NAD (such as the non-flushing form (niacinamide) and flushing form (niacin) of vitamin B3, so it can be useful to stack the two together in formulations.

L-Tryptophan sourcing is focused on identifying and purchasing from a reputable supplier and ensuring it is NON-GMO, gluten-free and vegan.

L-Tryptophan Dosing Principles and Rationale

L-Tryptophan is generally considered to be dose-dependent (see Neurohacker Dosing Principles) in the range it’s commonly dosed (between several hundred mg to several grams or more a day). It’s been estimated that an average adult diet provides about 800-1000 mg/day of L-tryptophan. In studies that have looked at augmenting the breakfast meal with L-tryptophan, amounts less than the amount in an average diet have been sufficient to produce positive subjective responses during the day, with sleep that night, and with overall body clock function. When taken prior to bed, a dose close to ¼ the daily average intake has been sufficient to support healthier deep sleep. These studies are consistent with L-tryptophan supplementation supporting healthier function when given in amounts that are less than what would be found in an average diet. 

L-Tryptophan Key Mechanisms

NAD(P) synthesis

  • L-tryptophan is a substrate in the de novo NAD+ synthesis pathway via the kynurenine pathway (KP)[1]
  • NAD+ can be converted to the coenzyme NADP+ by the enzyme NAD kinase[2]
  • NAD(H) and NADP(H) are key molecules in essential redox pathways of cellular metabolism and energy production[3]
  • NAD(H) is essential for the production of ATP through the citric acid cycle and oxidative phosphorylation[3]
  • NADP(H) is essential in many anabolic metabolic reactions, including DNA and RNA synthesis[3]
  • NADP(H) is a cofactor for some cytochrome P450 enzymes that detoxify xenobiotics[4]
  • NADPH also acts as a cofactor for glutathione reductase, the enzyme used to maintain reduced glutathione (GSH) levels[3]
  • NAD(H) and NADP(H) are essential for healthy aging[3]

Brain function

  • L-tryptophan is a precursor for serotonin (a neurotransmitter) and melatonin (a neurohormone) synthesis[5]
  • Upregulates the rate of serotonin synthesis[6,7]
  • Promotes social behavior[8,9]

Exercise performance (ergogenic effect)

  • Supports power output[10,11]
  • Delays time to exertion[10,11]

Social Cognition

  • Supports healthier social interactions[12–14]
  • Promotes charitable behaviors[15]


  • Nicotinic acid (niacin) and nicotinamide (niacinamide) as substrates for NAD synthesis. 


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[2] G. Magni et al., Cell. Mol. Life Sci. 61, 19–34 (2004).
[3] W. Ying, Antioxid. Redox Signal. 10, 179–206 (2008).
[4] D. S. Riddick et al., Drug Metab. Dispos. 41, 12–23 (2013).
[5] L. Palego, L. Betti, A. Rossi, G. Giannaccini, J. Amino Acids. 2016, 8952520 (2016).
[6] J. D. Fernstrom, Physiol. Rev. 63, 484–546 (1983).
[7] J. D. Fernstrom, J. Nutr. Biochem. 1, 508–517 (1990).
[8] L. Steenbergen, B. J. Jongkees, R. Sellaro, L. S. Colzato, Neurosci. Biobehav. Rev. 64, 346–358 (2016).
[9] S. N. Young, Philos. Trans. R. Soc. Lond. B Biol. Sci. 368, 20110375 (2013).
[10] C. Javierre, R. Segura, J. L. Ventura, A. Suárez, J. M. Rosés, Int. J. Neurosci. 120, 319–327 (2010).
[11] R. Segura, J. L. Ventura, Int. J. Sports Med. 9, 301–305 (1988).
[12] D.S. Moskowitz, G. Pinard, D.C. Zuroff, L. Annable, S.N. Young, Neuropsychopharmacology. 25, 277–289 (2001).
[13] A. Nantel-Vivier, R.O. Pihl, S.N. Young, S. Parent, S.A. Bélanger, R. Sutton, M.-E. Dubois, R.E. Tremblay, J.R. Séguin, PLoS One. 6 (2011) e20304.
[14] K. Hogenelst, R.A. Schoevers, M. Aan Het Rot, Int. J. Neuropsychopharmacol. 18 (2015).
[15] L. Steenbergen, R. Sellaro, L.S. Colzato, Front. Psychol. 5, 1451 (2014).