3-Iodotyrosine.
Research-backed amino acid with potential health benefits. It's a precursor to thyroid hormones. In theory, it gives your thyroid gland a building block. In practice, your body is good at making its own from iodine and tyrosine.
Reviewed March 2026
- Category
- Amino acid
What 3-Iodotyrosine is, and what it does.
- Does it work
- No. The evidence for supplementing with it directly is very weak. Better to ensure you have enough iodine and L-tyrosine instead.
- How much to take
- There's no established dose from human trials. Formulas often include 50-200 mcg. The best dose is probably zero.
- Time to feel it
- Nobody has measured an onset for it in people. It's studied as a step inside the thyroid gland and as a laboratory tool, not as something with a described daily timeline.
- The first dose
- Nothing. You will not feel this. It's not designed for an acute effect.
- With regular use
- Unclear. There's no solid long-term data in humans for supplementation. The risk of disrupting normal thyroid function outweighs any unproven benefit.
- How well tolerated
- Risky for anyone with a known thyroid condition. For healthy people, it's a gamble. Messing with hormone precursors without medical supervision is a bad idea.
- How it feels
- It shouldn't feel like anything. It's not a stimulant or a relaxant. If you feel 'off', stop taking it.
- The overlooked benefit
- Your body doesn't waste the iodine on it. A dedicated enzyme strips that iodine straight back off for reuse, which is why free monoiodotyrosine doesn't pile up in the blood.
100 to 250mcg a day is where 3-Iodotyrosine works.
Source: Based on thyroid hormone precursor pharmacology
The proof, claim by claim.
These words describe the research, not the molecule's worth. Research strength is how much work stands behind one claim, and it is never a product score.
3-Iodotyrosine is documented in the library; the clinical read is in the queue. Nothing about the strength of the research prints until the read is done.
- Intermediate in normal thyroid hormone formationNarrative review
- Iodine recycling by iodotyrosine deiodinaseNarrative review
- Competitive inhibition of tyrosine hydroxylase in laboratory workIn vitro study
- Shared transport with other large neutral amino acidsIn vitro study
Questions people ask about 3-Iodotyrosine.
- Is this the same as iodine?
- No. It's the amino acid tyrosine bonded with one iodine atom. Your thyroid does this internally.
- Will it help me lose weight?
- Unlikely. While thyroid hormones drive metabolism, taking a single precursor isn't a reliable or safe way to boost them.
- Is it better than taking L-Tyrosine?
- No. Just get enough L-Tyrosine and iodine from your diet. Let your body do the chemistry.
- Can I take it with my thyroid meds like levothyroxine?
- Absolutely not without talking to your endocrinologist. This can seriously interfere with your treatment.
- Is it natural?
- It's a natural compound your body makes. The supplement version is synthesized in a lab.
- Is it a stimulant?
- No. It has no direct stimulant properties. If a product with it feels stimulating, check for caffeine or other additives.
Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
3-iodo-L-tyrosine is a substrate analogue of tyrosine and a competitive inhibitor of tyrosine hydroxylase, the rate-limiting enzyme that converts tyrosine to L-DOPA. Supplying tyrosine raises the concentration of the natural substrate and shifts that competition. The relationship is textbook enzyme kinetics and needs no trial to state.
Phenylalanine is hydroxylated to tyrosine and then feeds the same catecholamine pathway that 3-iodotyrosine acts on. Both aromatic amino acids also cross the intestinal wall and the blood-brain barrier on the large neutral amino acid transporter, so they compete for the same carrier. Halogenated tyrosine analogues use that carrier too.
Monoiodotyrosine forms when thyroid peroxidase attaches iodine to tyrosyl residues inside thyroglobulin, which makes iodine availability the upstream condition for its formation in the body. A synthesised 3-iodotyrosine ingredient does not add usable iodine to that pathway on its own. The link runs from iodine to the iodotyrosine, not the other way.
Iodotyrosine deiodinase, the enzyme that strips iodine back off monoiodotyrosine so the iodide can be reused, is a flavin-dependent enzyme requiring FMN and reducing equivalents. Riboflavin is the dietary source of that flavin cofactor. Without adequate flavin status the salvage step runs less well, which is settled biochemistry.
The iodothyronine deiodinases that handle thyroid hormone metabolism are selenoproteins carrying selenocysteine at the active site, so selenium status governs that branch of iodine handling. Iodotyrosine deiodinase is a separate flavin enzyme and is not selenium dependent, a distinction often blurred in supplement copy. Both enzymes sit in the same overall iodine economy.
Tyrosine hydroxylase is a non-heme iron enzyme, so iron occupies the catalytic centre of the very step that 3-iodotyrosine competes at. Iron status therefore sets the ceiling on that reaction independently of substrate supply. This is enzyme biochemistry rather than a supplementation finding.
Aromatic L-amino acid decarboxylase requires pyridoxal 5-phosphate to convert L-DOPA into dopamine, the step immediately after the reaction 3-iodotyrosine inhibits. Anything acting on the hydroxylase changes what is available for that decarboxylation. The cofactor relationship itself is settled.
Dopamine beta-hydroxylase uses ascorbate as its electron donor when converting dopamine to norepinephrine, one step further along the same pathway. Ascorbate also helps keep the iron in the tyrosine hydroxylase active site in its reduced state. Both are described cofactor roles.
Dopamine beta-hydroxylase is a copper-dependent enzyme, so copper status affects the catecholamine pathway downstream of the tyrosine hydroxylase step. Copper and its cofactor partners are handled separately from the iodine side of this molecule's chemistry. The relationship is textbook.
Tryptophan, tyrosine and their halogenated analogues all cross membranes on the large neutral amino acid transporter and compete with one another for it. Loading one aromatic amino acid reduces carrier capacity for the others. This is why aromatic amino acids are usually spaced apart rather than taken together.
Nothing specific on file for 3-Iodotyrosine. Match the label to the daily amount above, and tell your doctor what you take.
Not medical advice. Show the label to your pharmacist.What 3-Iodotyrosine actually does.
3-iodo-L-tyrosine, also written monoiodotyrosine, is L-tyrosine carrying a single iodine atom on the aromatic ring at position 3.
Monoiodotyrosine forms inside the thyroid gland when thyroid peroxidase iodinates tyrosyl residues within thyroglobulin, and coupling of iodinated tyrosines is the step that builds thyroid hormone.
Iodotyrosine deiodinase, a flavin-dependent enzyme, removes iodine from monoiodotyrosine and diiodotyrosine so that the iodide can be reused rather than lost, which is why free monoiodotyrosine does not normally accumulate in circulation.
3-iodo-L-tyrosine acts as a competitive inhibitor of tyrosine hydroxylase, the rate-limiting enzyme of catecholamine synthesis, and is used in laboratory work for exactly that property.
Where 3-Iodotyrosine comes from.
Chemists start with the ordinary amino acid tyrosine and attach one iodine atom to its ring. The hard part is stopping at one, because the reaction happily adds a second, so the mixture is separated and checked before packaging in light-proof containers.
Chemically synthesised. The molecule is identical to the one a plant or an animal makes, and building it deliberately means a known purity, a fixed dose and no crop contaminants. For several nutrients this is the only route that reaches a usable amount.
Fermentation-derived or synthetic L-tyrosine is the starting amino acid.
Iodine is introduced onto the phenolic ring using an iodinating system under controlled pH and temperature, which favours substitution at position 3.
Mono-, di- and non-iodinated species are separated, since iodination readily overshoots to the diiodo product.
Structure is confirmed by chromatography and spectroscopy and iodine content is measured against the theoretical value.
Dried and packaged with light protection, since carbon-iodine bonds on the aromatic ring degrade under light and heat.
The forms it comes in.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.