Thyroid Support

Best-in-class: Thyrocsin

Thorne Thyrocsin. Per two-capsule serving: L-tyrosine 500 mg, vitamin C 200 mg, vitamin E 67 mg, KSM-66 ashwagandha root extract 90 mg, zinc 5 mg, copper 500 mcg, iodine 225 mcg as potassium iodide, selenium 100 mcg as L-selenomethionine and vitamin B12 100 mcg as methylcobalamin, taken twice daily. The iodine is 150% of the Daily Value per serving, and the label permits two servings.

How Thyroid Support actually works

A cofactor blend for hormone synthesis and conversion — iodine as substrate, tyrosine as the backbone, selenium and zinc for the deiodinases converting T4 to T3, and often guggul or ashwagandha. It targets the conversion step rather than gland output.

Where to get Thyroid Support

The evidence for Thyroid Support

Graded by what exists behind each claim.

✅ Clinically validated

• Supplies established thyroid cofactors — iodine (hormone backbone), tyrosine (precursor), selenium/zinc (T4→T3 conversion).
• Supports healthy thyroid function when cofactors are lacking.

📊 Correlative data

• Low selenium/zinc/iodine status tracks with impaired thyroid output and conversion.

🧪 Theoretical / extrapolated benefits

• Cofactor support helps a struggling-but-not-diseased thyroid; it does not replace medication in true hypothyroidism.

How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →

What Thyroid Support actually does

First, what is in it, because the card's safety note describes a different product. The Thyrocsin label filed with the NIH Dietary Supplement Label Database lists, per two-capsule serving: vitamin C 200 mg, vitamin E 67 mg, vitamin B12 100 mcg as methylcobalamin, iodine 225 mcg as potassium iodide, zinc 5 mg, selenium 100 mcg as L-selenomethionine, copper 500 mcg, L-tyrosine 500 mg, and KSM-66 ashwagandha root extract 90 mg, taken two capsules twice daily Office of Dietary Supplements 2025. There is no kelp and no glandular in it. The card warns about both. At the directed four capsules a day the actual daily load is iodine 450 mcg, selenium 200 mcg, L-tyrosine 1,000 mg, zinc 10 mg, copper 1,000 mcg and ashwagandha 180 mg, and everything below is written against those numbers.

The gland, at the steps that have names. The sodium–iodide symporter on the basolateral thyrocyte membrane concentrates iodide against a gradient. At the apical surface, DUOX2 generates hydrogen peroxide and thyroid peroxidase uses it to oxidize iodide and attach it to tyrosyl residues within the thyroglobulin polypeptide — making monoiodotyrosine and diiodotyrosine, which TPO then couples: DIT plus DIT gives T4, MIT plus DIT gives T3. The gland secretes mostly T4. Conversion to the active hormone happens outside it, by the iodothyronine deiodinases DIO1 and DIO2, which remove an iodine from the outer ring.

Selenium is the only ingredient here that is a catalytic requirement rather than a raw material, and that distinction is the page. All three deiodinases are selenoproteins: they carry selenocysteine in the active site, and without selenium the enzyme is not slow, it is not built. Glutathione peroxidase and thioredoxin reductase are also selenoproteins, and inside a thyrocyte their job is to dispose of the hydrogen peroxide TPO needs, which is why the thyroid holds among the highest selenium concentrations of any tissue. So selenium sits at two different steps — activating T4, and protecting the cell that makes it.

Iodine is the backbone, and it is the ingredient with a genuinely biphasic dose-response. Iodine is not a cofactor; it is part of the hormone, four atoms of it per T4 molecule. But raising iodide above a threshold acutely inhibits organification — the Wolff–Chaikoff effect — and a normal thyroid escapes it within days by down-regulating the symporter. A thyroid that cannot escape stays blocked and becomes hypothyroid; a nodular thyroid handed extra substrate can instead run away into thyrotoxicosis. Both directions from the same excess are the documented consequences of iodine excess Leung 2014, and no other ingredient in this bottle can cause disease in two opposite directions.

Tyrosine is the ingredient with the weakest mechanistic claim, and it is worth saying why rather than letting it pass. The tyrosines that get iodinated are not free amino acid in the bloodstream; they are residues embedded in thyroglobulin, a 660 kDa protein the follicular cell synthesizes itself. Free tyrosine has never been shown to be rate-limiting for thyroid hormone synthesis in a human, tyrosine is a non-essential amino acid made from phenylalanine, and 1,000 mg a day Office of Dietary Supplements 2025 is a fraction of ordinary dietary intake. It is on the label because it is the right noun.

And the ashwagandha is the only ingredient with a placebo-controlled human thyroid trial behind it, in subclinical hypothyroidism Sharma 2018 — at a dose the bottle does not contain, which is the next section.

Cell, rodent, human — and where it stops

There is no trial of this blend. What follows is each ingredient against the dose that produced its evidence.

Selenium: the dose in the bottle is exactly the trial dose, and exactly the dose of the trial that found harm. Seventy women (mean age 47.5 ± 0.7) with autoimmune thyroiditis took 200 mcg of selenium a day for three months. Thyroid peroxidase antibody concentrations fell to 63.6% of baseline (P = 0.013) against 88% on placebo (P = 0.95); in those starting above 1,200 IU/mL the fall was a mean 40% against a 10% rise on placebo; and nine selenium-treated patients normalized their antibodies against two on placebo (P = 0.01) Gartner 2002. Thyrocsin delivers 200 mcg/day at the directed dose Office of Dietary Supplements 2025. That is a genuine match, and it is the strongest thing on this page. The same 200 mcg/day is the dose at which a long-term randomized trial in 1,202 people, followed a mean 7.7 years, found type 2 diabetes in 58 selenium recipients against 39 on placebo — 12.6 versus 8.4 cases per 1,000 person-years, hazard ratio 1.55 (95% CI 1.03 to 2.33) Stranges 2007. One number, one trial each way.

Iodine: three times the requirement, in a country that already has enough. The label's own 225 mcg per serving is 150% of the Daily Value, so four capsules is 300% Office of Dietary Supplements 2025. Whether that is trivial or serious depends entirely on the thyroid receiving it Leung 2014 — and on what else is in the diet, which is where the seaweed literature matters: iodine content of commercially available edible seaweeds is highly variable Teas 2004, and the interaction between seaweed iodine and thyroid function is a recognized problem in its own right Smyth 2021. Somebody eating seaweed regularly and taking this product has an intake nobody has measured.

Ashwagandha: a fifth to a third of the trial dose. The subclinical hypothyroidism trial used 600 mg a day of a root extract for eight weeks and reported normalization of thyroid indices Sharma 2018. Thyrocsin carries 90 mg per serving, 180 mg a day Office of Dietary Supplements 2025 — 30% of the trial dose. Nobody has tested 180 mg against placebo for a thyroid endpoint.

Zinc, copper, B12, C and E: real biochemistry, no thyroid trial. Zinc 10 mg and copper 1,000 mcg a day Office of Dietary Supplements 2025 are nutritionally sensible amounts in a sensible ratio. No randomized trial has shown that adding either to a replete adult changes TSH, free T4 or free T3.

So the specific obstacle is the one this whole category hides: every ingredient argument is a deficiency argument, and the buyer is usually not deficient. Selenium repletion changes antibodies in autoimmune thyroiditis Gartner 2002; iodine repletion changes hormone output in iodine-deficient populations. Neither says anything about a selenium-replete, iodine-sufficient adult with a normal TSH and a tired week. The second obstacle is that this product's two most active ingredients have opposite risk profiles at the same dose — selenium at 200 mcg helps thyroid antibodies Gartner 2002 and raises diabetes incidence Stranges 2007; iodine at 450 mcg feeds hormone synthesis and can block it Leung 2014. A blend cannot optimize both.

Thyroid Support — which form, and does it matter

The form choices on this label are, unusually, the right ones, and they should be credited before the criticism. The iodine is potassium iodide — a defined salt with a known iodine content — not kelp. That matters because seaweed iodine content varies enormously between and within products Teas 2004, so a kelp-based thyroid blend cannot state its own iodine dose accurately Smyth 2021, and this one can. The selenium is L-selenomethionine, the organic form that incorporates into body protein, rather than sodium selenite. The zinc and copper are bisglycinate chelates. The B12 is methylcobalamin Office of Dietary Supplements 2025. This is a carefully specified label.

One form caveat that cuts the other way, and it is the reason the two selenium trials are not directly comparable. The antibody trial used sodium selenite Gartner 2002; the diabetes trial reports its dose but not its chemical form Stranges 2007; the bottle contains L-selenomethionine Office of Dietary Supplements 2025. Selenomethionine is incorporated non-specifically in place of methionine in body proteins and accumulates with continued intake, which selenite does not do to the same degree. So the product's form resembles the trial that found the diabetes signal more closely than the trial that found the antibody benefit. That is an inference from the metabolism of the two forms rather than a head-to-head result, and it is labeled as one.

KSM-66 is a real specification and it is stated. Naming the extract Office of Dietary Supplements 2025 is what allows the comparison with the 600 mg/day trial dose Sharma 2018 to be made at all; most botanicals on most blends cannot be checked this way.

The form question that decides whether the whole category is safe is the one this product happens to pass. Ten commercially available thyroid supplements were assayed by mass spectrometry. Nine of ten contained detectable T3 (1.3 to 25.4 mcg per tablet) and five of ten contained T4 (5.77 to 22.9 mcg per tablet); five delivered more than 10 mcg of T3 a day and four delivered T4 at 8.57 to 91.6 mcg a day Kang 2013. Those are pharmacologic quantities of prescription hormone in products sold as supplements. They came from glandular ingredients — bovine or porcine thyroid tissue. Thyrocsin contains no glandular Office of Dietary Supplements 2025, so it is not in that class. The single most useful thing a reader can take from this page is the rule that follows: if a thyroid product lists thyroid tissue, glandular, or an animal organ of any kind, assume it may contain real thyroid hormone until an assay says otherwise.

And the label carries a warning the card does not. The filed label says: if pregnant, nursing, or trying to conceive, do not use this product Office of Dietary Supplements 2025. Iodine requirements rise in pregnancy and thyroid status in early gestation is consequential, so this is a warning worth surfacing rather than leaving on the bottle.

What would have to be true, and how you would know it was not

1. tsh and free t4, before and at twelve weeks, and the prediction is nothing in a normal thyroid. In a euthyroid adult with normal iodine intake, predict TSH and free T4 unchanged. Nothing in this bottle acts on a gland that is not short of something, and no trial of this blend exists. If TSH moves in either direction, that is information: it means one of the two active ingredients found a thyroid that was not in the state you assumed.

2. tpo antibodies, which is the one endpoint with a matching trial dose. In somebody who is TPO-antibody positive, predict a fall of roughly a third from baseline by twelve weeks, because 200 mcg/day of selenium took antibodies to 63.6% of baseline at three months Gartner 2002 and this product delivers 200 mcg Office of Dietary Supplements 2025. This is the single most defensible prediction on the page, and it requires knowing your antibody status before you start — which most buyers of thyroid support do not.

3. fasting glucose and hba1c — the prediction that cuts against the product, and it is the one nobody makes. Predict a drift upward in fasting glucose and HbA1c on sustained daily use, because the long-term randomized trial of 200 mcg/day of selenium found a higher incidence of type 2 diabetes Stranges 2007 and this product delivers that dose every day with no stop date. A thyroid supplement whose most likely measurable effect is on glucose rather than on thyroid is a genuinely uncomfortable prediction, which is exactly why it belongs here. Twelve months, not twelve weeks — this is a slow endpoint.

4. Urinary iodine, the measurement that turns a guess into a number. A spot urinary iodine concentration is the standard population measure of iodine status and it is cheap. On 450 mcg/day Office of Dietary Supplements 2025 predict it rises well above the sufficiency range. That matters most for anyone who also eats seaweed, where content is unpredictable Teas 2004 Smyth 2021: the two sources together are the realistic route to an intake that causes trouble Leung 2014, and one urine sample tells you whether you are there.

5. free t3 and reverse t3, for the deiodinase claim specifically. The selenium argument is that T4-to-T3 conversion improves. That predicts free T3 up, or the free T3 to reverse T3 relationship shifting, in someone who was selenium-deficient. In someone who was not, predict both flat. Draw them at baseline and twelve weeks; if free T4 is unchanged and free T3 has risen, the conversion claim has been demonstrated in one person, which is more than the marketing has ever done.

What nobody has tested yet

Nobody has ever run this blend, or any multi-cofactor thyroid blend, against placebo. Every number on this page belongs to a single ingredient tested alone Gartner 2002 Stranges 2007 Sharma 2018. A twelve-week, two-arm trial with TSH, free T4, free T3 and TPO antibodies is not an exotic study, the product has been on sale for over a decade, and it does not exist.

Nobody knows what 450 mcg of iodine a day does to a TPO-antibody-positive euthyroid adult. That is precisely the person most likely to buy a thyroid support product, and it is the person for whom iodine excess carries the clearest risk of tipping into overt hypothyroidism Leung 2014. The experiment is one arm, twelve weeks, TSH every four. Its absence is the largest gap in this category.

Nobody has tested whether the selenium diabetes signal appears with selenomethionine at 200 mcg in a blend. The diabetes finding came from a 1,202-person skin-cancer prevention trial that reports its dose and not its chemical form Stranges 2007; the thyroid benefit came from selenite Gartner 2002; the product is selenomethionine Office of Dietary Supplements 2025. Whether the risk and the benefit travel with the same chemical form has never been asked, and it determines whether this product's central trade-off is real or an artifact of comparing two different molecules.

And nobody has repeated the supplement assay on the current market. The finding that nine of ten thyroid supplements contained detectable T3 Kang 2013 is from 2013. The category has grown substantially since. A re-run of that assay on today's top-selling products is a week of mass spectrometry and would be the single most consequential piece of consumer-protection work anyone could do in this aisle.

Thyroid Support — its own safety story, not its category's

The risk that makes this the highest-stakes blend on the site is that iodine can cause thyroid disease in both directions. Excess iodine precipitates hypothyroidism in a thyroid that cannot escape acute organification block — typically an autoimmune, previously-treated or otherwise compromised gland — and precipitates thyrotoxicosis in a nodular gland handed extra substrate Leung 2014. Somebody who starts this product because they feel sluggish, and who has undiagnosed Hashimoto's disease, is taking 450 mcg/day Office of Dietary Supplements 2025 of the one nutrient most likely to make that specific condition worse. Thyroid labs before, not after.

The category risk this product does not carry, stated so it can be used elsewhere. Nine of ten assayed thyroid supplements contained detectable triiodothyronine, at up to 25.4 mcg per tablet, and five delivered more than 10 mcg of T3 a day Kang 2013. That is an unlabeled prescription drug at a clinically active dose, capable of causing atrial fibrillation and bone loss, and capable of suppressing TSH so that subsequent testing is uninterpretable. Thyrocsin contains no glandular Office of Dietary Supplements 2025 and is not one of those products. Any thyroid blend that does contain glandular should be assumed to be, until assayed.

Selenium is the ingredient whose ceiling is closest. Two hundred micrograms a day is the dose that lowered thyroid antibodies Gartner 2002 and the dose that raised diabetes incidence in a long-term randomized trial Stranges 2007, and this product delivers it daily and indefinitely Office of Dietary Supplements 2025. Selenium also has the narrowest margin of any trace element in common supplement use — selenosis presents as hair loss, brittle nails, a garlic odor on the breath and peripheral neuropathy. Anyone stacking this with a multivitamin, a separate selenium capsule or Brazil nuts is adding these together, and they add rather than average.

The medication interaction that matters most is the obvious one, and it has a direction. On levothyroxine, iodine and selenium both alter the substrate and the conversion step around a fixed replacement dose, so TSH will move and the dose will need rechecking — six weeks after starting, which is how long TSH takes to re-equilibrate. On antithyroid drugs the iodine is working directly against the treatment. Neither of those is a reason for a blanket prohibition; both are reasons the prescriber has to know.

Two the label states and the card does not. The filed label says do not use if pregnant, nursing or trying to conceive Office of Dietary Supplements 2025. And ashwagandha in subclinical hypothyroidism raised thyroid hormone indices Sharma 2018 — which is the intended direction in that population and the wrong direction entirely in someone with a nodule, subclinical hyperthyroidism, or Graves' disease. Three ingredients in this bottle push thyroid output up. None of them knows which thyroid it is in.

Sources read for this page

• Office of Dietary Supplements, National Institutes of Health. Thyrocsin (Thorne) -- filed Supplement Facts panel, 2 capsules twice daily: per 2-capsule serving vitamin C 200 mg, vitamin E 67 mg, vitamin B12 100 mcg as methylcobalamin, iodine 225 mcg as potassium iodide, zinc 5 mg, selenium 100 mcg as L-selenomethionine, copper 500 mcg, L-tyrosine 500 mg, KSM-66 ashwagandha root extract 90 mg; no glandular, no kelp; on market. NIH Dietary Supplement Label Database, label recorded 2025
• Kang GY, et al. Thyroxine and triiodothyronine content in commercially available thyroid health supplements. Thyroid 2013;23(10):1233-1237 · PMID 23758055
• Leung AM, Braverman LE. Consequences of excess iodine. Nature Reviews Endocrinology 2014;10(3):136-142 · PMID 24342882
• Gartner R, et al. Selenium supplementation in patients with autoimmune thyroiditis decreases thyroid peroxidase antibodies concentrations. Journal of Clinical Endocrinology and Metabolism 2002;87(4):1687-1691 · PMID 11932302
• Stranges S, et al. Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial.. Annals of Internal Medicine 2007 · PMID 17620655
• Sharma AK, et al. Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. The Journal of Alternative and Complementary Medicine, 2018 · PMID 28829155
• Smyth PPA. Iodine, Seaweed, and the Thyroid. European Thyroid Journal 2021 · PMID 33981614
• Teas J. Variability of iodine content in common commercially available edible seaweeds. Thyroid 2004 · PMID 15588380

How you would know if it worked

Thyroid Support — safety & side effects

Bloodwork to run alongside Thyroid Support

Baseline first, then again at 8–12 weeks.

The Thyroid — First Look panel covers these in one order — 2 markers, $19.80 with the discount applied.

Check results you already have → · All 103 markers A–Z

Thyroid Support — frequently asked questions

Thyroid Support inside a finished plan

One arm of 2 Protocol Blueprints, free to read in full.

What Thyroid Support is used for

Thyroid Support appears under 3 goals in the goal router.

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