Short answer. Your brain builds its mood messengers from amino acids in food: tryptophan becomes serotonin, phenylalanine and tyrosine become dopamine, and glutamate becomes GABA. Vitamin B6, as P-5-P, is the cofactor at the final step for all three. Only about 3% of the tryptophan you eat ends up as serotonin, and chronic stress pulls more of it away.
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Search for help with low mood or anxiety and the shelves fill up with "serotonin supplements" and "dopamine supplements". The idea underneath them is real biology: the chemical messengers that nerve cells use to talk to each other are built from the protein you eat. What the labels skip is everything between the plate and the brain, and that's where most of the interesting science sits.
This matters to a lot of people. The World Health Organization puts the number living with depression at about 322 million, and the number with an anxiety disorder at 470 million in 2023, which makes anxiety the most common mental health condition in the world (WHO depression fact sheet; WHO anxiety fact sheet). In Gallup's 2025 data from 140 countries, 36% of adults said they felt stress during a lot of the previous day (Gallup). And the global burden of mental disorders didn't fall between 1990 and 2019; their share of all health burden rose from 3.1% to 4.9% (GBD 2019 Mental Disorders Collaborators 2022, PMID 35026139).
Below: how amino acids become neurotransmitters, what happens in studies that take the raw material away, how stress gets in the way, and where our amino products fit.
How do amino acids become neurotransmitters?
Nine amino acids are essential, which in nutrition has a strict meaning: the body can't make enough of them, so they have to come from food. Two of those nine, tryptophan and phenylalanine, are the starting points for serotonin and dopamine. A third messenger, GABA, comes from glutamate, which the body makes itself.
Two kinds of nutrient do the work. Precursors are the raw material that becomes the messenger. Cofactors are the helpers an enzyme needs to make the conversion; they aren't built into the messenger. Vitamin B6 gets called a precursor a lot, but it's a cofactor. The body never turns B6 into serotonin; it just can't finish making serotonin, dopamine or GABA without it, because the enzymes at those finishing steps belong to the large family that depends on pyridoxal 5'-phosphate (Percudani and Peracchi 2003, PMID 12949584).
| Messenger | Made from | Cofactors along the way | Main jobs |
|---|---|---|---|
| Serotonin | Tryptophan | Iron and BH4, then B6 (P-5-P) | Mood steadiness, worry and impulse control, appetite, gut movement; the starting point for melatonin |
| Dopamine | Phenylalanine, then tyrosine | Iron and BH4, then B6 (P-5-P) | Motivation, reward, focus |
| Norepinephrine | Dopamine | Vitamin C and copper | Alertness and the stress response |
| GABA | Glutamate | B6 (P-5-P) | The brain's main brake; settles nerve activity |
| Glutamate | Glutamine and other amino acids | Several | The main "go" signal for learning and memory |
Which amino acid makes serotonin, and why does so little of it get there?
Tryptophan is the only precursor for serotonin. An enzyme that needs iron turns it into 5-HTP, and a second enzyme that needs B6 turns 5-HTP into serotonin. At night, the pineal gland takes that serotonin two more steps to melatonin.
Very little tryptophan takes this route. Only about 3% of dietary tryptophan is used to make serotonin anywhere in the body, while roughly 90% of tryptophan breakdown runs down a different route, the kynurenine pathway (Richard 2009, PMID 20651948). Getting into the brain is its own problem. Tryptophan shares one carrier at the blood-brain barrier with the other large amino acids, such as leucine, valine, phenylalanine and tyrosine, and that carrier is close to full at normal blood levels (Richard 2009, PMID 20651948). In rats, a carbohydrate meal raised brain tryptophan and serotonin, because insulin moves the competing amino acids into muscle (Fernstrom and Wurtman 1971, PMID 5120086).
Two more facts keep the picture honest. More than 90% of the body's serotonin is made in the gut, not the brain, and blood serotonin can't cross into the brain at all (Yano 2015, PMID 25860609). And a large umbrella review of the serotonin research found no consistent evidence that depression is caused by low serotonin (Moncrieff 2023, PMID 35854107). So the useful goal isn't "more serotonin". It's supply: enough raw material and enough cofactors for the body to make what it needs, where it needs it.
Which amino acid makes dopamine?
Dopamine starts from phenylalanine, an essential amino acid, which the body converts to tyrosine. Tyrosine becomes L-DOPA, and the same B6-dependent enzyme that finishes serotonin turns L-DOPA into dopamine. One more step, using vitamin C and copper, makes norepinephrine, the messenger behind alertness and the stress response.
That stress link shows up in the supplement research. A 2015 review of tyrosine studies found it helped thinking mainly in short, stressful or mentally demanding situations, the kind that temporarily drain dopamine and norepinephrine, and did little under ordinary conditions (Jongkees 2015, PMID 26424423). That's the pattern with most precursors: they help most when supply is the bottleneck.
How is GABA made, and why does it matter for anxiety?
GABA is made straight from glutamate, in one step, by an enzyme that needs vitamin B6. So the brain builds its main brake out of its main accelerator, and one nutrient sits right at that hinge. Anxiety research focuses on the amygdala, the brain's threat detector, where networks of GABA cells turn alarm signals down; researchers describe anxiety as trouble with that modulation (Nuss 2015, PMID 25653526).
What happens when tryptophan or tyrosine runs low?
Researchers can test this directly. In a depletion study, volunteers drink a large amino acid mix with one precursor left out, so blood levels of that precursor fall steeply for a few hours, then recover. It's an experiment, never a treatment. The best-established finding is that lowering serotonin function this way lowers mood in some people, though not in everyone (Young 2013, PMID 23428157).
| Who took part | What was removed | What happened |
|---|---|---|
| Healthy women before a stressful speaking and arithmetic task | Tryptophan, or phenylalanine and tyrosine | Lower mood after the stress test with either drink; tryptophan removal also lowered energy and raised irritability (Leyton 2000, PMID 10633491) |
| 20 people with panic disorder, not on medication | Tryptophan (blood levels down more than 80%) | No change at rest, but more anxiety and more panic attacks during a CO2 breathing test, 9 against 2 (Miller 2000, PMID 10755058) |
| 15 women recovered from depression, off medication | Tryptophan (down 75%) | 10 of 15 had a temporary return of low-mood symptoms (Smith 1997, PMID 9093253) |
| 20 autistic adults, not on medication (more in our autism article) | Tryptophan (down 86%) | 11 of the 17 who finished got worse, with more repetitive movements and more anxiety (McDougle 1996, PMID 8911222) |
| 16 healthy adults in a brain scanner | Phenylalanine and tyrosine | No change in average mood, but a weaker reward response in the nucleus accumbens (Bjork 2014, PMID 23995581) |
Who you are changes the result. Pooled across 45 tryptophan studies, depletion didn't lower mood in healthy volunteers, lowered it slightly in healthy people with a family history of depression, and lowered it moderately in people who'd had depression before (Ruhé 2007, PMID 17389902). The authors read that as a vulnerability trait rather than proof that low serotonin causes low mood. Taking a building block away and adding one aren't mirror images, either: none of these studies shows that extra tryptophan lifts mood.
Does stress lower serotonin?
Chronic stress can. Stress hormones switch on TDO, the liver enzyme at the start of the kynurenine pathway, and inflammation switches on its cousin IDO, so long-running stress and infections can shunt tryptophan away from serotonin (Höglund 2019, PMID 31024440). The kynurenine pathway already handles about 95% of dietary tryptophan breakdown (Badawy 2017, PMID 28469468). Short bursts of stress work differently and can briefly raise brain tryptophan (Höglund 2019, PMID 31024440). For what the magnesium, B-vitamin and ashwagandha stress trials found, see our stress research summary.
The blood data line up with that. Across 101 studies and 10,912 people, tryptophan and kynurenine ran lower in people with depression, and the kynurenine-to-tryptophan ratio ran higher (Marx 2021, PMID 33230205). A separate meta-analysis of 744 patients found lower plasma tryptophan in depression, most clearly in people who weren't taking medication (Ogawa 2014, PMID 25295433).
Why might amino acids run low if you eat protein?
For most people with a varied diet, they don't. The trouble usually sits between the plate and the brain, and four things come up again and again:
- Too little protein. Dieting, a small appetite or a short list of accepted foods all cut intake.
- Low stomach acid. Acid switches on pepsin, the enzyme that starts protein digestion, and acid-reducing medicines turn it down on purpose.
- Chronic stress, which diverts tryptophan down the kynurenine pathway.
- Low zinc. Zinc runs more than 300 enzymes (McCall 2000, PMID 10801957), among them protein-digesting enzymes and the one stomach cells use to make acid.
You don't have to guess. A fasting plasma amino acid test, ordered by a clinician, reports the whole set from one blood draw. Results are read against reference ranges for age, and one low value is a question for your clinician rather than a verdict. Normal results are good news, and a reason to spend your money elsewhere.
Where do ASDHelp's amino products fit?
We think of it as four steps, a menu rather than a stack. Most people need one or two of them, added one at a time and given at least four weeks before anyone judges the result.
1. Broad amino acid support. Amino supplies nine free-form amino acids (eight essentials plus arginine), which the gut absorbs without digesting them first, along with alpha-ketoglutarate and 14 mg of B6 as P-5-P. The label serving is 4 capsules a day between meals, under 3 g of amino acids in total, so it's a top-up rather than a protein source. It contains no tryptophan, and it does contain phenylalanine, so it isn't for anyone told to limit phenylalanine, including people with PKU. For days when meals don't happen, MITOboost Protein Powder is the drink route: 15 g of rice protein per scoop with a full vitamin and mineral panel, including 5 mg of zinc and 15 mg of B6.
2. Digestion and zinc. Free-form amino acids skip digestion, which is the point of Amino. If digestion itself is the weak link, the digestive enzymes and the order to introduce them are in our Gut Reset protocol. Use one zinc source at a time; our zinc page lists the upper limits.
3. The B6 cofactor. Vitamin B6 P-5-P gives 30 mg of the active coenzyme per capsule; the adult label serving is one capsule a day with food. Count your B6 first. Amino already has 14 mg and MITOboost Protein Powder 15 mg, and in every ASDHelp plan we keep the total at or under 25 mg a day for adults and 10 mg for children, unless a clinician sets a different amount. High-dose B6 can damage sensory nerves (Schaumburg 1983, PMID 6308447), so stop and call your clinician if you notice tingling, numbness or burning in your hands or feet. P-5-P is for when B6 is the only gap, not an add-on to the other two. Our vitamin B6 page covers food sources and limits, and one of each explains why we never stack the same nutrient twice.
4. Targeted neurotransmitter support. Spectrum Neurotransmitter Support is the only one of the five that lists tryptophan (80 mg) and tyrosine (290 mg) on its label, from 6 g of pea and rice protein, with NAC, DHA, CoQ10 and phosphatidylserine. The label serving is one scoop for ages 4 and up; adults take it with a practitioner's guidance. It has no added B6, and one shake a day is plenty. For adults only, Lithium Orotate supplies 4.8 mg of the trace mineral per capsule; the label serving is one capsule twice a day with food (more on our lithium orotate page). Lithium inhibits an enzyme called GSK-3 (Klein and Melton 1996, PMID 8710892), and in mouse brain cells longer-term exposure shifted the balance between excitatory and inhibitory signalling (Khayachi 2021, PMID 34077150), but those are lab findings. Check with your physician first if you have a kidney or heart condition or take diuretics, ACE inhibitors or medicine for mood. It isn't for pregnancy or breastfeeding, and never combine two lithium products.
For whole product sets built around one goal, see our Mood Support, Calm Support and Stress and Resilience protocols.
What does the research not show?
It doesn't show that any supplement can stand in for professional care for anxiety or low mood, and none of these products is meant to. A Cochrane review found 108 studies of tryptophan and 5-HTP for depression, and only 2, with 64 people in total, were good enough to count; the reviewers called the evidence inconclusive (Shaw 2002, PMID 11869656). Extra tyrosine helps mainly under short-term stress (Jongkees 2015, PMID 26424423). No placebo-controlled trial has tested low-dose lithium orotate for mood, and no one has trialled these products together as a set. People differ, too: the same depletion drink barely touched most healthy volunteers and hit others hard (Ruhé 2007, PMID 17389902).
If you're taking medicine for mood or anxiety, ask your prescriber before adding amino acids or lithium. If you're in crisis or thinking about harming yourself, call or text 988 in the US, or your local emergency number, now.
Sources
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These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is education, not medical advice; talk to your healthcare provider before starting a supplement, and a child's amounts are set by the child's clinician.