Roadmap: Supplementing T3/T4

Warning

• It is important to avoid creating deficiencies; when the metabolism is increased, demand for nutrients rises.
• If liver health is impaired, acute hunger may arise when skipping meals.
• It is wise to explore all other options and supplements before trying thyroid supplementation.
• Adequate cholesterol is required (above 160, ideally 200), as well as vitamin D and B intake so getting blood labs to check for things like total cholesterol, vitamin D, PTH, lactic acid, and prolactin will be useful references.
• Supplementing thyroid can sometimes reduce the rate of metabolism, by allowing cells to retain enough magnesium, which stabilizes ATP.
  • The goal is raising the efficiency, not burning as many calories as possible.

Reasons to refrain from supplementing thyroid

• In rare cases, addressing the diet and factors such as sunlight, chronic stress/grief, etc. is enough to bring a person to euthyroidism.
  • Enough carbohydrate comes first. In women eating keto long term, three weeks at about 200 g a day raised free T3 by roughly 43% with calories unchanged, while TSH, T4 and reverse T3 held steady.
• Thyroid supplementation requires constant self-awareness and willingness to experiment with dose and timing.

Starting with 1 grain felt amazing at first, but caused adrenaline surges, overheating, and nightmares; splitting and eventually cutting to ¼–½ grain worked perfectly; then sunshine and better lifestyle made even that dose too much and I quit entirely.

— HubblyBubbly Emporium

The average person (especially older, unwell, or depressed individuals) may not be capable of responsibly titrating or stopping thyroid medication on their own. One community account describes doctors often over-prescribing thyroid and being reluctant to adjust the dose once started (anecdotal, not a documented outcome). The average person (especially older, unwell, or depressed individuals) may not be capable of responsibly titrating or stopping thyroid medication on their own.

Ray's articles

• Thyroid: Therapies, Confusion, and Fraud
• Thyroid, insomnia, and the insanities: Commonalities in disease
• TSH, temperature, pulse rate, and other indicators in hypothyroidism
• Water: swelling, tension, pain, fatigue, aging

Symptoms associated with hypothyroidism

• Symptoms: Fatigue, lethargy, weight gain, cold extremities.
  • The full list of symptoms associated with hypothyroidism of common hypothyroidism symptoms here
• Physiological Biomarkers: Low body temperature, low pulse rate, slow reaction time, slow Achilles tendon reflex time.
• Blood tests: Generally, high TSH, cholesterol, PTH, and prolactin are associated with lowered thyroid function.

A more thorough self diagnosis can be found here.

Supplementation

It would be safe to start with T3 (triiodothyronine) only:

For more detail on T3 itself (structure, mechanism, and full dosing thresholds), see Triiodothyronine.

• Shorter half-life (~12 hours) makes gauging the effects easier.
• Small doses (1–3 mcg) can act within minutes; a starting dose of about 1 mcg can already produce a noticeable effect, and 5 mcg with a meal is another way to start.
• Helps stabilize glucose/glycogen, reduce adrenaline sensitivity, and gradually brings a sense of calm over several days.

T4 (thyroxine) is trickier:

For more detail on T4 itself (structure, mechanism, and the monotherapy critique), see Thyroxine.

• Longer half-life (~2 weeks) means it builds up slower within the tissues, and requires long-term planning.
• If liver function is impaired, T4 may convert to reverse T3, lowering metabolism.
• During the night and sleep, T4 can help suppress TSH and other stress hormones better than T3-alone.
• Oral T4 absorption needs adequate stomach acid; if TSH stays high despite a high T4 dose, consider H. pylori or other malabsorption before raising the dose further; direct T3 bypasses this absorption step entirely. See Thyroxine for the eradication-study numbers.

NDTs

Naturally Desiccated Thyroid supplements vary in their consistency and potency due to the varying diets and climates the animals were exposed to, which makes supplementing with them very tricky.

Purchase

Cynoplus (T4+T3) and Cynomel (T3) can be acquired from here and here.

Idealabs thyroid supplements can be purchased here, but keep in mind that a single drop contains too much thyroid, dosing may be inaccurate, and that T3 can be inactivated due to the solvents used.

Synthroid (T4 only) is usually what is prescribed by doctors, so finding a source of T3 and combining them would be the best way to approach.

Bad batches

• Thyroid medication is heat sensitive.
• Anecdotally, bad batches are a thing.

DIY thyroid

You can theoretically, at least, make it yourself, if you for example boil milk with oysters or seaweed, a source of iodine and trace minerals, the prolonged boiling will create iodinated casein which in effect works like thyroid hormone, you can make it right in your kitchen, if it happened you are not able to buy thyroid in a pharma classical form. The reaction between trace minerals, casein, and iodine will produce an active thyroid-like substance.

— Ray Peat

Link to recipe

Dosing and possible deficiencies to watch out for

When you first start taking thyroid again, your tissues will need some extra magnesium, during the time when the dose is increasing, and when the mineral balance is restored your temperature and metabolic rate might decrease a little. Orange juice, milk, and coffee are good for the main minerals, while salting your food to taste.

— Ray Peat

Dosing should be approached carefully and methodically. The demand for nutrients goes up.

It is best to begin with the lowest dose and increase incrementally (every 2 weeks when supplementing with T4), while checking temperature and pulse. Around the end of the 2-week mark, the need for nutrients such as selenium (to convert the accumulated T4 to T3) magnesium, vitamin A, vitamin D3 and B vitamins (B1 and B3) may increase. Seafood such as tuna, shrimp, oysters and beef liver are all good sources of selenium, B vitamins, and Vitamin A.

People with a total cholesterol above 200, adequate vitamin A, and D, and minimal digestive issues respond best to thyroid.

Zinc and vitamin A

Zinc and vitamin A are both needed for thyroid hormone to actually work once it gets into the cell, not just to be made or absorbed, so a deficiency in either can blunt the effects of supplementing even when the dose looks adequate on paper.

In practice, low zinc or vitamin A shows up as abnormal thyroid labs that correct with repletion:

• Zinc deficiency looks like low free T3 with high reverse T3. Of 13 disabled patients with low free T3, 9 turned out zinc deficient; 12 months of zinc supplementation normalized free T3 and lowered reverse T3 (case series). In two zinc-deficient college women, 4 months of zinc raised total T3 and resting metabolic rate (case study). (In zinc-deficient growing rats, growth still failed even though T3 action in the liver looked normal, so zinc's effect on growth isn't purely a T3 story (rat).)
• Vitamin A deficiency looks like high TSH with high total T4. In 138 Moroccan children with iodine and vitamin A deficiency, worse vitamin A status meant higher TSH, bigger thyroids, and more goiter; giving vitamin A alongside iodized salt over 10 months lowered TSH and goiter rates compared with placebo (RCT). A 2022 review of animal studies found the same pattern mechanistically: vitamin A deficiency reduces the liver's conversion of T4 to T3 while blood T4 and T3 rise (review). (Rat studies also show vitamin A deficiency or large excess both lower how well T3 binds its receptor in the liver and brain, and that T3 itself can partly restore the receptor when it's deficient.)

The human findings above are what matters practically: check for zinc and vitamin A status alongside the usual thyroid cofactors, since low levels of either can make supplementation look less effective than it should be.

Increased vitamin A increases your need for vitamin E, phosphate should be balanced with calcium, and it's important to watch thyroid function.

— Ray Peat

Thyroid Calculator

Preparation	Amount	Unit	Note
Grains		grains	Pivot for all rows
NDT tablet mass		mg	~60 mg per grain (tablet weight)
NDT USP T3 content		mcg	~9 mcg T3 per grain (USP)
NDT USP T4 content		mcg	~38 mcg T4 per grain (USP)
T3-only rough equivalent		mcg	Rule of thumb: 25 mcg T3 ≈ 1 grain activity
T4-only rough equivalent		mcg	Rule of thumb: 100 mcg T4 ≈ 1 grain activity

Combined T3 + T4 (synthetic mix at chosen ratio)

Uses the same 25 mcg T3 ≈ 1 grain and 100 mcg T4 ≈ 1 grain activity model (not USP gland content). Peat often prefers T3-heavier mixes (e.g. 1∶2 or 1∶3 T3∶T4) than the default 1∶4.

Setting	Value
Desired Ratio (T3 : T4)	:
T3 mcg : T4 mcg (for selected grains)	:

T3 monotherapy

The metabolic effects of T3 last for 4 hours, but the TSH suppressing effects last a couple days. If you've been running on stress for a long time and relying on stress hormones for energy, taking T3 can have a "kick" to it as it sensitizes the adrenals, so starting with small amounts and splitting the dose throughout the day is smart. It may take several days for adrenaline levels to normalize. Salt and sugar are useful to keep the adrenaline "kick" at bay. In Ray's experience, he consistently got heart palpitations from taking a big dose of T3, as it made him severely hypothyroid by causing the liver to inactivate the excess T3, so it's best to start with 1 mcg and adjust from there (anecdote as relayed by @RayPeatHeadShop, not a primary transcript).

Taking 25 mcg of T3 only in the morning for a few weeks, Ray Peat found his heart pausing for seconds at a time around sunset; 5 to 10 mcg rubbed on the roof of the mouth restored the rhythm within seconds. A large dose taken at once gets partly inactivated by the liver, while a few micrograms per hour supplies what the body can use without suppressing the liver's or the gland's own production. Starting around 1 mcg and adjusting from there is the safer course.

Some contexts to consider

• Season
  • Lower doses in the warmer months; higher in colder months. At high latitudes the need rises sharply in winter: half a grain in summer became two grains in winter for Ray Peat himself.
• Altitude
  • People at higher altitude naturally need less due to their increased retention of carbon dioxide.
• Protein intake
  • High protein diets can blunt thyroid activity due to the thyroid suppressing amino acids such as methionine, tryptophan, histidine, and cysteine.

Practical tips

• A pill crusher and milligram scale can be used for more accurate dosing since eyeballing can easily be inaccurate.
• It is paramount to check both pulse and temperature after dosing to measure any effects.
  • Salt, sugar, low-dose beta blockers, and cyproheptadine may be useful early on if adrenaline sensitivity is high.
  • Some supportive foods are gelatin, sugar, orange juice, chicken broth, milk, and ice cream. Even breathing into a paper bag for increasing tissue CO₂ can help.

Big picture

Thyroid supplementation is highly individualized. T3 offers quick, fine-tuned effects, while T4 requires patience and careful management. A complete diet and adequate micronutrition (selenium, magnesium, vitamins) is crucial for thyroid hormones to work effectively.

Demystifying Thyroid Supplementation summary sheet

Section	Takeaways	Notes
Symptoms	Low thyroid symptoms vary widely: fatigue, cold hands/feet, dry skin, low libido, etc.	No one-size-fits-all - use resting pulse (85 bpm) and morning temperature (~98°F) as the ideal markers to reach.
Dosing Strategy	Start low (e.g., 1/8 to 1/4 Cynoplus tablet); increase slowly every 2 weeks.	T4 builds up slowly (2-week half-life), so avoid changing the dose too soon.
T3/T4 Ratio	Peat favors T3-heavy ratios (1:3 or 1:2) vs standard 1:4 (T3:T4).	T3 supports brain, mood, energy and is more "brain protective".
Troubleshooting	Poor thyroid response may mean missing: protein, B-vitamins, magnesium, calcium, and carbohydrates.	Also check for vitamin D deficiency, infection, or excess dietary phosphate.
Cofactor Synergy	Thyroid increases metabolic rate → nutrient needs go up	Liver & oysters = best sources of critical cofactors (vit A, copper, selenium, zinc).
Climate Consideration	Colder weather may require a higher dose (e.g., 1 full tablet vs ¼ in a warm climate).	No one-size-fits-all - use resting pulse (85 bpm) and morning temperature (~98°F) as markers.

Barnes’ Standard Dose: ~2 grains/day (1 grain of NDT is USP-standardized to 9 mcg T3 + 38 mcg T4, not the 12.5/50 split sometimes quoted online).

Danny’s Personal Use: Cynoplus in evening (T4+T3), and Cynomel in daytime. Supplement according to need eg. more in the winter.

Physiological dose: the body produces about 4 mcg of T3 per hour, so taking 10 or 20 mcg at once is unphysiological and can interfere with regulatory processes. Danny Roddy relays the same advice as no more than 10 mcg at once, taken with food to slow absorption, against a liver output of 3-4 mcg an hour.

Stopping thyroid supplementation

Best to taper off slowly while measuring temperature, heart rate and food intake. Timing it so you don’t have any serious events coming up may be wise.

You might get sick or get headaches, brain fog, poor sleep and lose appetite for a couple days. It will stop after the thyroid resumes it's baseline function. Anecdotally, some report that starting and stopping T3 resolved their hypothyroidism long-term when the underlying stress had been acute rather than lifelong; this is a community report, not a documented outcome.

There are no long term negative effects of starting and stopping exogenous thyroid medication since the gland is quite versatile and will adjust its size and function within a day or two. In isotope studies, subjects whose glands were fully shut off by large thyroid doses all returned to normal gland activity within 2 or 3 days of stopping.

Eating animal thyroid

People who eat fish heads or other animal heads generally consume the thyroid gland along with the brain. Historically this was a significant dietary thyroid source: fish heads, chicken necks, and traditional stews and sausages all included glandular tissue. This is a food-level, unmeasured source, not a substitute for dosed supplementation when a real deficiency is present.

Relevant quotes

Getting your blood glucose up by eating some carbohydrates will activate your thyroid, increasing the conversion of thyroxine to the active T3.

— Ray Peat

The body normally produces several micrograms of T3 every hour, but if a large amount of supplementary thyroid is taken in a short time, the liver quickly inactivates some of the excess T3. Taking a few micrograms per hour provides what the body can use, and doesn't suppress either the liver's or the thyroid's production of the hormone.

— Ray Peat

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