L-Tryptophan
An essential amino acid from food, taken most often at bedtime for sleep.
- Sleep
- Mood
- Stress and appetite
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is L-Tryptophan?
Tryptophan is an essential amino acid: the body cannot build it, so it has to arrive in food. What is actually needed each day is small, a few milligrams for every kilogram of body weight, and yet many adults choose to take far more than that, up to four or five grams, and one review says they do it mainly for mood or for sleep. The reason is what the body does next with it: tryptophan is the starting material for serotonin, and further along the same line, for melatonin. It is sold as the plain amino acid, written L-tryptophan on the label, and the same substance goes into animal feed.
Why do people take L-Tryptophan?
Sleep
The thinking. Sleep is what most people reach for tryptophan for, and bedtime is when they take it. The idea follows the chemistry one stop further on: melatonin, the hormone that sets the body’s daily clock, is made out of serotonin, and tryptophan is what serotonin is made from. Drowsiness would count as a side effect anywhere else; one review of supplement use notes that for the people taking it at bedtime, it is the point.
What research has found. One review pooled the sleep trials and found that people spent less time awake after first dropping off, with a gram or more a day doing more than smaller amounts. The other parts of sleep the review measured did not shift. Research here is still young: a few studies so far, mostly pointing the same way.
Mood
The thinking. Mood is the other long-standing reason. Low serotonin in the brain has been linked for decades with low mood and with poor memory, and tryptophan is the material serotonin is built from, so the thinking is simply to supply more of it. Researchers have leant on the same idea for years, raising and lowering people’s tryptophan on purpose to watch what mood does.
What research has found. A review gathered eleven randomised trials in healthy adults. Four of them found a difference from the control group in ratings of low feelings and of happy feelings; ratings of aggression did not move. The amounts used ran from about a seventh of a gram up to three grams a day, alongside ordinary meals. Only a few studies have measured this so far, though they mostly agree.
Stress and appetite
The thinking. A smaller group take it for stress, and for the eating that tends to come with it, when a hard day turns into reaching for something sweet. The thinking is the serotonin one again, pointed at appetite as well as at mood. There is a twist to it: stress itself changes how much tryptophan is left over for serotonin, which is the reason some researchers give for topping it up at exactly those times.
What research has found. One trial gave adults tryptophan or a dummy capsule for a week, then put them through a stress test. Cortisol, the stress hormone, fell and appetite held steady afterwards, but only in the people carrying one particular version of a serotonin gene, and not in the rest. Few studies have measured this yet, so there is little to go on either way.
What does L-Tryptophan do in the body?
Tryptophan comes in through food, inside protein, and the body has no way of making its own. Some of what reaches the brain is converted into serotonin, and serotonin is converted further along into melatonin. That short chain is why one amino acid turns up in writing about mood and about sleep alike.
Most of it never travels that way. Reviewers describe only a small share going to serotonin, while a much larger share takes a second route, the kynurenine pathway, which is the body’s one way of building NAD+ from scratch, the substance every cell leans on to make energy. A third share is worked over by gut bacteria into substances called indoles, which act on a receptor in the lining of the gut. How much goes down each route is not fixed: the enzyme that opens the second route is turned up by stress hormones, and a related one by inflammation, so long stretches of stress or infection steer tryptophan away from serotonin.
What do people say about taking L-Tryptophan?
These are anecdotes people have shared, not evidence.
What people like
- Three of these five threads sit in one parenting community, and in four of the five sleep, not mood, is the reason described.
- Those who say it helped describe a gentle nudge towards sleep rather than anything heavy, and a couple pair it with magnesium at bedtime.
- A few describe long-standing broken sleep settling after starting it, one of them after more than ten years of trouble sleeping.
- Where mood rather than sleep is the reason, the draw people describe is that the body turns it into serotonin.
Common complaints
- In three of these threads people describe it doing nothing at all, or working for a night or two and then fading.
- A small number report something physical they did not expect: a pounding heartbeat at a larger amount, and a higher morning blood sugar reading.
- The 1989 contaminated batch and the withdrawal that followed still come up in two of the threads, usually as a reason to hesitate.
How people take it
- Amounts described run from about 500 mg to 1,500 mg taken at night, with one parent describing a much smaller amount for a child.
- Bedtime, or an hour before it, is the timing nearly everyone describes; nobody in these threads describes taking it in the morning.
- In two threads hardly anyone had actually tried it and the replies turn to food instead, so first-hand accounts are thin.
- Checking it with a doctor or pharmacist barely comes up; the one label point raised is that it says not for under-18s.
Read from these public discussions:
- Magnesium for sleep (Mumsnet, 2025)
- Treating anxiety with food/supplements (Mumsnet, 2012)
- Supplements to boost serotonin levels in children? (Mumsnet, 2012)
- Tryptophan anyone? (Insomnia Coach, 2011)
- L-Tryptophan for Insomnia (Earth Clinic, 2015)
What forms of L-Tryptophan are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| L-Tryptophan | The amino acid itself, sold as the free form that labels write as L-tryptophan. | 220 mg |
What else is worth knowing about L-Tryptophan?
- Tryptophan raises serotonin, which is what several prescribed medicines do as well. A review of its use as a supplement reports that the occasional side effects seen at larger amounts, tremor, nausea and dizziness, can appear whether it is taken on its own or alongside a medicine that acts on serotonin, such as an antidepressant, and it describes rare cases of serotonin syndrome, the reaction to too much serotonin at once. For anyone already on a medicine of that kind, this is the thing to raise first.
- In 1989 a condition called eosinophilia myalgia syndrome appeared and was quickly connected to tryptophan supplements; its main features were disabling muscle pain and a high count of one kind of white blood cell. One review says the cause was shown to be not tryptophan itself but a contaminant in certain production batches. A second, written in 2023, says the link between impurities left by the manufacturing process and the syndrome has been examined at length without a clear conclusion.
- Two trials reported on how well it was tolerated. In one crossover study seventeen healthy young women took between one and five grams a day for three weeks at a time, and their weight, mood scores and blood and urine markers were unchanged at every amount; in another, three grams a day for three weeks brought no change in gut or psychological scores. Both ran a few weeks only, and both were in healthy adults.
- Labels give the amount per serving, and a serving may be more than one capsule, so the figure on the front is worth reading next to the number of capsules it covers. Across the studies on this page, daily amounts ran from about a seventh of a gram up to five grams.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (11 studies)
- The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression. (2022, meta-analysis)
- A systematic review of the effect of L-tryptophan supplementation on mood and emotional functioning. (2021, systematic review)
- Effect of sub chronic tryptophan supplementation on stress-induced cortisol and appetite in subjects differing in 5-HTTLPR genotype and trait neuroticism. (2014, randomised trial)
- Effects and side effects associated with the non-nutritional use of tryptophan by humans. (2012, review)
- Safety concerns regarding impurities in L-Tryptophan associated with eosinophilia myalgia syndrome. (2023, review)
- Impact of the Gut Microbiota on Intestinal Immunity Mediated by Tryptophan Metabolism. (2018, review)
- Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis. (2016, review)
- Tryptophan Metabolic Pathways and Brain Serotonergic Activity: A Comparative Review. (2019, review)
- Kynurenine pathway, NAD + synthesis, and mitochondrial function: Targeting tryptophan metabolism to promote longevity and healthspan. (2020, review)
- How important is tryptophan in human health? (2019, review)
- Tryptophan metabolites modulate inflammatory bowel disease and colorectal cancer by affecting immune system. (2022, review)
How much does L-Tryptophan cost?
That depends on the form and the pack, so we work out the price of the same dose of every L-Tryptophan product we can find and rank them.