The building blocks
Amino acids
Amino acids are the small molecules your body strings together to build every peptide and protein — and the best-studied, lowest-hype part of this whole reference. The evidence here runs decades deep and mostly concerns nutrients you already eat, which makes it unusually settled: less to sell, less to argue about. It's the steady ground the rest of the site is built on.
41 amino acids
- 5-HTP
5-HTP is a direct precursor to serotonin with real human data for mood and appetite. It reaches the brain — and needs care alongside SSRIs.
- Alanine
Alanine is a non-essential amino acid central to how muscle and liver trade fuel and clear nitrogen. Its roles, food sources, and the evidence.
- L-Arginine
L-Arginine is the amino acid the body turns into nitric oxide to widen blood vessels. Its roles, food sources, and what human research shows.
- Asparagine
Asparagine is a non-essential amino acid, first found in asparagus, that helps handle nitrogen and build proteins. Its roles, sources, and the evidence.
- Aspartic acid
Aspartic acid is a non-essential amino acid driving the urea cycle and nucleotide synthesis. Its roles, food sources, and what the research shows.
- BCAAs
BCAAs — leucine, isoleucine and valine — are the muscle-signaling amino acids. What they do, where to get them, and why whole protein often beats the powder.
- Beta-alanine
Beta-alanine, the tingle-inducing amino acid that buffers muscle fatigue: how it builds carnosine, why it makes you tingle, and what the human trials show.
- Betaine (TMG)
Betaine, or trimethylglycine, is a methyl donor that lowers homocysteine and is studied for strength and power. Here's the honest evidence.
- L-Carnitine / ALCAR
The l carnitine peptide search points to a non-peptide nutrient and prescription drug. Compare forms, human evidence, safety, and 2026 status.
- Carnosine
Carnosine is a dipeptide of beta-alanine and histidine, concentrated in muscle and brain, studied as an antioxidant and anti-glycation agent.
- Citrulline Malate
Citrulline malate is L-citrulline bound to malic acid and a top pre-workout ingredient. Does the malate add anything, or is it just a delivery form?
- Creatine
Creatine, the most studied sports supplement there is: how it fuels short bursts of power, where you get it, and what the human trials show for muscle.
- L-Cysteine
L-Cysteine is the sulfur amino acid that limits how much glutathione your body can build. Its roles, food sources, and what the research shows.
- GABA
GABA is the brain's main calming neurotransmitter. Whether the oral supplement actually reaches the brain is still debated — here's the evidence.
- L-Glutamic acid
L-Glutamic acid is the body's main excitatory neurotransmitter and a metabolic hub. Its roles, food sources, and what the research does and doesn't show.
- L-Glutamine
L-Glutamine is the body's most abundant free amino acid, fueling gut and immune cells. Its roles, food sources, and what human research shows.
- Glutathione
The glutathione peptide is a three-amino-acid antioxidant. See what oral, liposomal and injectable forms can—and cannot—claim from human research.
- Glycine
Glycine, the smallest amino acid: a collagen building block, glutathione precursor, and calming neurotransmitter. Its roles, food sources, and the evidence.
- L-Histidine
L-Histidine is an essential amino acid behind carnosine, histamine and hemoglobin. Its roles, food sources, and what the research does and doesn't show.
- Homocysteine
Homocysteine is an amino acid your body clears with folate, B12 and B6. What high levels mean for heart and brain — and what the trials actually showed.
- Hydroxyproline
Hydroxyproline is the modified proline that stabilizes collagen's triple helix. How the body makes it using vitamin C, and what supplements can't promise.
- L-Isoleucine
L-isoleucine, a branched-chain essential amino acid tied to muscle energy and glucose uptake: its roles, food sources, and the honest evidence.
- L-Citrulline
L-Citrulline, the watermelon amino acid behind the blood-flow buzz: how it boosts nitric oxide, where you get it, and what the human exercise trials show.
- L-DOPA
L-DOPA (levodopa) is the dopamine precursor that reaches the brain: the cornerstone Parkinson's medicine, and the active compound in Mucuna bean supplements.
- L-Ornithine
L-Ornithine helps the urea cycle clear ammonia, and small human studies link it to less fatigue and better sleep. Here's what the research shows.
- L-Theanine
L-Theanine, the calming amino acid in green tea: how it creates relaxed focus, why it pairs with caffeine, and what the human trials show for stress.
- L-Leucine
L-leucine, the branched-chain amino acid that switches on muscle protein synthesis: its roles, food sources, and what human research shows.
- L-Lysine
L-lysine, the essential amino acid behind collagen crosslinks and carnitine: its roles, food sources, and what the cold-sore research shows.
- L-Methionine
L-methionine, the sulfur-containing essential amino acid that starts every protein and fuels methylation: its roles, sources, and evidence.
- NAC (N-acetylcysteine)
NAC (N-acetylcysteine), an FDA-approved drug and glutathione precursor: how it thins mucus, reverses acetaminophen overdose, and what the human evidence shows.
- L-Phenylalanine
L-phenylalanine, the essential amino acid that builds tyrosine, dopamine and adrenaline: its roles, food sources, and the honest evidence.
- L-Proline
L-Proline is the amino acid that gives collagen its twist and strength. Its roles, food sources, and what the research does and doesn't show.
- Pyrrolysine
Pyrrolysine is the 22nd amino acid — a lysine cousin that only certain microbes use, coded by a hijacked stop signal. What it is, and why labs borrow it.
- SAMe
SAMe (S-adenosylmethionine) is the body's universal methyl donor, with real human evidence for depression and osteoarthritis. Here's the research.
- Selenocysteine
Selenocysteine, the 21st amino acid: cysteine with selenium instead of sulfur. Its role in your selenoproteins, and why selenium is the real nutrient.
- L-Serine
L-Serine is a non-essential amino acid feeding brain chemistry, cell membranes and one-carbon metabolism. Its roles, food sources, and the evidence.
- Taurine
Taurine, the amino acid packed into energy drinks and your heart, brain and muscle: what it does, where you get it, and what the human research shows.
- L-Threonine
L-threonine, the essential amino acid your gut lining leans on for mucus: its roles, food sources, and what the research actually shows.
- L-Tryptophan
L-Tryptophan is the essential amino acid your body turns into serotonin and melatonin. Its roles, food sources, and what human research shows.
- L-Tyrosine
L-Tyrosine is the amino acid your body turns into dopamine and adrenaline. Its roles, food sources, and what human research shows on stress and focus.
- L-Valine
L-valine, one of the three branched-chain amino acids your body cannot make: its roles in muscle and energy, food sources, and the evidence.