The raw material your brain converts into serotonin and then melatonin - the two molecules most directly responsible for mood stability and sleep onset.

L-Tryptophan is an essential amino acid that supports sleep by serving as the precursor to both serotonin and melatonin — the two signals that regulate your sleep–wake cycle.

Once it crosses the blood–brain barrier (via the transporter it shares with amino acids like leucine and valine), tryptophan boosts serotonin synthesis in the brain's raphe nuclei, promoting calm and shortening the time it takes to fall asleep. At night, under the direction of the body's internal clock, that serotonin is converted into melatonin in the pineal gland — raising nocturnal melatonin and reinforcing healthy circadian rhythm.

Together, serotonin and melatonin shift the body toward its "rest and restore" state, lowering arousal and easing you into sleep. Clinical studies show that around 1 g of L-Tryptophan at bedtime can meaningfully shorten sleep onset and improve restorative slow-wave sleep — especially for those who struggle to fall asleep or deal with mild insomnia.

https://www.sciencedirect.com/science/article/pii/S2475299123108912

https://academic.oup.com/sleep/article-abstract/12/4/345/2742684?redirectedFrom=PDF

https://pubmed.ncbi.nlm.nih.gov/469515/

https://schlafapnoe-heilen.de/wp-content/uploads/2023/10/meta-analysis-The-impact-of-tryptophan-supplementation-on-sleep-quality.pdf
https://pubmed.ncbi.nlm.nih.gov/469515/