If you read one ingredient entry on this page, make it this one. The deiodinase enzymes that convert T4 into active T3 are selenoproteins — selenium is not assisting that reaction from the sidelines, it is a structural component of the enzyme performing it. Selenium is also required by the glutathione peroxidase family, which is what handles the hydrogen peroxide generated inside the gland as a normal byproduct of building hormone. Two different jobs, one mineral.

The form is L-selenomethionine, an amino-acid-bound organic selenium, rather than sodium selenite or selenate. It is better absorbed and better retained than the inorganic salts and it costs more, which is why the cheap end of this category doesn't use it. At 273% of the Daily Value this is a real nutritional amount rather than a token, and that means it stacks — read the selenium question in the FAQ below before you add it to a multivitamin, a greens powder, or a Brazil nut habit.

• Supports healthy thyroid hormone metabolism
• Supports normal T4-to-T3 conversion
• Supports antioxidant enzyme activity

Iodine is the element that gives thyroid hormone its name and its function — T4 carries four iodine atoms, T3 carries three. Without adequate iodine the gland cannot assemble hormone at all, which is why iodine deficiency remains one of the most consequential nutritional deficiencies worldwide.

We put exactly 150 micrograms in here, which is the adult Daily Value, and that number is a deliberate decision rather than a cost decision. Iodine is the ingredient the thyroid category most often overdoes. High-dose iodine products carrying twelve or fifty milligrams exist, and iodine is genuinely one of the few nutrients where more is not better — excess intake can disturb thyroid function in either direction, and it can matter a great deal in people with an autoimmune thyroid condition. A full nutritional amount is what belongs in a daily formula. If you and your physician have decided you need more than that, that is a supervised decision, not a shelf decision.

• Supports normal thyroid hormone synthesis
• Supports healthy metabolic function

This is the reception ingredient. Thyroid hormone works by binding a nuclear receptor, and that receptor operates as a heterodimer with the retinoid X receptor — a vitamin A dependent partner. Which means vitamin A status sits underneath the final step of the whole chain: whether the cell can actually read the signal it has been sent. Vitamin A also participates in the regulatory conversation upstream at the level of TSH signaling.

This is retinyl acetate, preformed vitamin A, not beta-carotene. Preformed retinol does not require the conversion step that carotenoids do, which is an advantage for reliability and a reason to pay attention to your total intake, because preformed vitamin A accumulates in a way carotenoids do not. Add up what you get here, what is in your multivitamin, and what is in a cod liver oil if you take one. And if you are pregnant, trying to become pregnant, or nursing, do not take this product — see the FAQ.

• Supports healthy thyroid hormone receptor function
• Supports normal cellular signaling
• Supports immune and visual health

Zinc appears at more than one point in this system. It is a cofactor in the enzymes involved in thyroid hormone metabolism, it is structurally involved in the zinc-finger domain of the thyroid hormone receptor itself, and zinc status and thyroid status track together closely enough in the literature that each is worth checking when the other is in question.

Ten milligrams is 91% of the Daily Value — a full nutritional amount, and deliberately not a high-dose zinc product. Sustained high-dose zinc competes with copper absorption, and a daily formula you intend to stay on is not the place to run that risk. If you are also taking a separate zinc product, add the two together before you decide.

• Supports normal thyroid hormone metabolism
• Supports healthy immune function
• Supports normal hormone receptor function

Tyrosine is the backbone. Thyroid hormone is built by attaching iodine atoms to tyrosine residues on a protein scaffold inside the gland, so tyrosine is one of the two literal raw materials in the whole process. It is also the precursor to dopamine, norepinephrine and epinephrine, which is why it shows up in cognitive and stress-load research separately from anything thyroid-related.

An honest note on this one, because it is the kind of thing we would rather say than have you work out later: tyrosine is a non-essential amino acid and a normal protein-containing diet supplies several grams of it a day. This 500 milligrams is a supportive addition to that pool, not the difference between having tyrosine and not having it. The acute cognitive research on tyrosine also uses far higher amounts, typically dosed by bodyweight into the multi-gram range. We include it because it belongs in the architecture of a thyroid formula and because it is cleanly disclosed — not because 500 milligrams is a research-level dose. See the dose ledger below.

• Supports normal thyroid hormone synthesis
• Supports catecholamine production
• Supports mental focus under load

Ashwagandha is the most studied adaptogen in the Western literature, and its presence in a thyroid formula is not decorative. Thyroid signaling and the stress axis are coupled — sustained stress load influences the conversion step, and the reverse relationship holds as well. Ashwagandha is here to support the body's normal adaptation to that load, which is the environment the rest of this formula has to work in.

Ashwagandha has also been studied specifically in relation to thyroid hormone levels, and that cuts both ways: it is a reason it is in this formula, and it is exactly why anyone taking thyroid medication needs their prescriber to know they started this product. That is not a footnote — read the medication FAQ below before your first capsule.

• Supports the body's normal stress response
• Supports mood and mental clarity
• Supports normal thyroid hormone balance

Guggul is the resin of the mukul myrrh tree and has one of the longer traditional-use records in Ayurvedic practice. Its modern interest to formulators is the guggulsterone fraction, which has been studied in relation to the T4-to-T3 conversion step and in relation to lipid metabolism. It sits in handoff 03 on the map above alongside selenium, working the same stage from a different direction.

Guggul is also the ingredient in this formula with the widest interaction profile. Guggulsterones influence drug-metabolizing enzyme activity and have been reported to affect the blood levels of several medication classes, including some heart medications and hormonal contraceptives, and guggul has been associated with changes in clotting parameters. The interaction FAQ below names the specific classes. Standardized to 10%, the panel amount delivers 15 milligrams of guggulsterones, which is below the amounts used in the published human trials — see the ledger.

• Supports normal T4-to-T3 conversion
• Supports healthy metabolic function
• Supports healthy lipid metabolism

Forskolin is one of the more mechanistically interesting compounds in botanical supplementation because its target is unusually well characterized: it activates adenylate cyclase, the enzyme that produces cyclic AMP. Cyclic AMP is the second messenger sitting underneath TSH signaling inside the thyroid cell, which is the pathway involved in hormone release. That is a specific, describable mechanism rather than a vague traditional-use story.

This is ForsLean®, the branded root extract from Sabinsa standardized to 10% forskolin — the material the human research in this space was run on, which is why we specified it rather than a generic coleus powder. Being straight with you about the amount: 50 milligrams of a 10% extract delivers 5 milligrams of forskolin, and the published ForsLean® human work used substantially more extract per day than this panel carries. It is in here as a targeted addition to a four-stage formula, not as a standalone forskolin product. The ledger below states the gap in numbers.

• Supports normal cyclic AMP signaling
• Supports healthy thyroid hormone release
• Supports healthy metabolic rate

Glandular concentrates are a traditional practice in functional and naturopathic formulating, based on the idea of supplying whole tissue as nutritional support for the corresponding tissue. Adrenal is here because the HPA axis and thyroid function are coupled: a system under sustained stress load behaves differently at the conversion and reception steps than a rested one does.

We are going to be more honest about this category than most labels are. Glandulars do not have the controlled human dose-response literature that the vitamins, minerals and standardized botanicals on this panel have. There is no established effective amount to compare 100 milligrams against, because the trials that would establish one have not been run. It is included as traditional nutritional support, it is disclosed at its exact amount, and we are not going to build a mechanism story around it that the evidence doesn't carry.

• Traditional nutritional support for the adrenal-thyroid relationship
• Supports normal stress adaptation

The same category as the adrenal above, and the same honesty applies. This is bovine thyroid tissue concentrate included as traditional whole-tissue nutritional support at 16 milligrams, disclosed on the panel.

What we will not tell you is that this is a bioidentical or natural version of thyroid medication. It is not. That framing appears constantly in this category and it is wrong — a dietary supplement is not a substitute for prescribed thyroid hormone, and nobody at IOH is suggesting you treat it as one. If you take levothyroxine, liothyronine, natural desiccated thyroid, or an antithyroid medication, this product is a conversation to have with your prescriber before you start it, not instead of them.

• Traditional nutritional support for thyroid tissue

DHEA is an adrenal steroid precursor and it sits in this formula on the adrenal side of the adrenal-thyroid relationship, at one milligram — a nominal amount, and far below the 25 to 50 milligram amounts used in the human research on DHEA supplementation. We are stating that plainly rather than letting the ingredient name do work the amount does not support.

One milligram or not, DHEA carries obligations that we are not going to bury. It is a substance prohibited at all times by the World Anti-Doping Agency and banned by the NCAA and the major professional sporting bodies. If you are drug-tested in any capacity — competitive sport, certain occupations, military service — do not take this product. It is also a prescription-only substance in a number of countries outside the United States, including Canada, the United Kingdom, Australia and New Zealand. And it is not appropriate for anyone under 18, anyone who is pregnant or nursing, or anyone with a hormone-sensitive condition. Read the FAQ below.

• Precursor to adrenal steroid hormones
• Included at a nominal supportive amount