Thyroid optimization — DTE-first

The premise

Thyroid hormone is the body's pace-setter. Every cell expresses thyroid receptors; the hormone tunes basal metabolic rate, body temperature, cardiac output, lipid handling, mood, cognition, and reproductive function. The active hormone at the receptor is Free T3, not Free T4 and not TSH. T4 is largely a pro-hormone — it has to be converted to T3 by a family of selenium-dependent enzymes called 5′-deiodinases before it does meaningful work at the cellular level.

There are three deiodinase types, and you need to know what each one does because the distinction is what justifies treating the way Nimbus treats:

• Type I (D1): liver, kidney, thyroid. Generates circulating T3 and also drives reverse-T3 inactivation. Sensitive to propylthiouracil.
• Type II (D2): CNS, pituitary, retina, heart, skin, skeletal muscle, brown adipose. The dominant route by which peripheral tissues make their own intracellular T3 from T4. High circulating T4 down-regulates D2, which means T4-monotherapy at high doses can paradoxically lower active tissue T3.^{[bianco-2019]}
• Type III (D3): CNS, skin, placenta. Inactivates T3 to reverse T3. Up-regulated by illness, stress, starvation, certain drugs.

Disruptors of deiodinase activity that come up in clinical practice: propylthiouracil, beta-blockers, high-iodide loads, endocrine disruptors and heavy metals, starvation, hypothyroidism itself, uncontrolled diabetes, uremia. The practical implication is that serum T4 (even Free T4) does not reliably predict the T3 the tissues actually see, and TSH — set by the pituitary's local D2 — does not reliably predict tissue T3 either.

This module trains the prescriber to (1) target Free T3 and symptoms rather than TSH, (2) prefer desiccated thyroid extract (DTE) over levothyroxine monotherapy, (3) run the levothyroxine-to-DTE conversion correctly, and (4) follow a documentation rule that protects the practice from the FDA Boxed Warning every thyroid hormone label carries.

Pre-test — anchor on the target

Thyroid physiology — TSH, FT4, FT3, the deiodinase types

The classic hypothalamic-pituitary-thyroid (HPT) axis: TRH → TSH → thyroid gland → T4 (~80%) and T3 (~20%). Most T3 the tissues use is generated peripherally from T4 by D1 and D2. The pituitary's TSH set-point reflects its own local D2 activity — which is why a "normal" TSH does not guarantee adequate T3 elsewhere in the body.

Two clinical consequences of the deiodinase architecture matter on every visit:

1. T4-only therapy is biochemically incomplete. High Free T4 down-regulates D2; over months, peripheral T3 falls even as the lab "looks good." This is why some levothyroxine patients remain symptomatic with a TSH inside the standard reference range.^[hoang-2013]
2. T3-only therapy suppresses TSH and ultimately starves the system of T4 reserve. D2 needs substrate. Long-term T3 monotherapy produces a hyper-then-hypo pattern.

The Nimbus default is replace both — DTE if the patient has no pork allergy or religious restriction, otherwise levothyroxine + liothyronine.

Numeric targets

Every thyroid follow-up at Nimbus reads off the same target sheet. Memorize this table.

DTE-first rationale — why combination T4+T3 outperforms T4 monotherapy

DTE (Armour, NP Thyroid, WP Thyroid, compounded equivalents) is desiccated porcine thyroid. It contains T4 and T3 in the natural porcine ratio plus small amounts of T1 and T2. Patients absorb and respond to it differently than to synthetic T4 alone or to synthetic T4 + T3 split tablets — most patients feel better, sleep better, and report clearer cognition on DTE than on equivalent T4 monotherapy.^{[hoang-2013-pref]}

The randomized literature on T4+T3 combination therapy versus T4 monotherapy is mixed in the aggregate but consistent in one place: in the symptomatic subgroup who did not feel well on levothyroxine alone, combination therapy improved well-being and quality-of-life measures.^{[bunevicius-1999]} The Wiersinga synthesis of the European Thyroid Association working group reaches the same practical conclusion: a structured trial of combination therapy is reasonable in the persistently symptomatic patient.^{[wiersinga-2012]}

Initiation — start low, titrate by symptoms

The DTE titration ladder is the load-bearing piece of this module. The timeline below shows the cadence at a glance; the widget underneath walks through it interactively; the prose covers the AFib carve-out, the twice-daily dosing decision, and the rule that stops escalation at 4 grains/day.

Standard adult start: 0.5–1 grain DTE PO QAM, empty stomach, 30 minutes before food, drink, or other medications. Plain water is fine; if local water is high-mineral, distilled is preferable for the morning dose window.

Cardiac carve-out: AFib history, SVT history, or known cardiac sensitivity → start 0.25 grain QAM and titrate by 0.25 grain monthly rather than the standard 0.5–1 grain monthly. Slower is safer; the goal is symptom improvement without provoking arrhythmia.

Up-titration: by 0.5–1 grain monthly (0.25 grain monthly in cardiac patients) until Free T3 is in the 4.0–4.3 pg/mL band and symptoms resolve. Re-check TSH + Free T3 + Free T4 at 4–6 weeks after each dose change.

Twice-daily dosing: if afternoon fatigue persists at 1.5–2 grains QAM, split the dose (AM + early-PM). Cap the second dose at 2–3 PM — later than that and DTE drives insomnia.

Ceiling and the T3 add-on rule: the maximum is 2 grains BID (4 grains/day). If symptoms persist at 4 grains/day, add liothyronine 5–25 mcg rather than continuing to escalate DTE — at higher DTE doses, additional T4 stops adding peripheral T3 because of D2 down-regulation.

Levothyroxine → DTE conversion algorithm

This is the most frequently mis-run conversion in DTC. The trap: a clinician converts at "equivalent" dose and the patient feels worse at week 2 because the stored T4 pool that was buffering them has run out.

The algorithm:

1. Confirm the patient is truly hypothyroid (has been on levothyroxine for an evidenced indication) or is a symptomatic euthyroid-by-labs patient electing the off-label trial — document accordingly.
2. Stop levothyroxine.
3. Start DTE at the equivalent dose: 100 mcg levothyroxine ≈ 1 grain DTE. So 50 mcg → 0.5 grain; 100 mcg → 1 grain; 150 mcg → 1.5 grain.
4. At 2 weeks: double the DTE dose. This compensates for T4 storage depletion. Without this step the patient crashes between weeks 2 and 6.
5. Continue titrating by symptoms and Free T3 every 4–6 weeks until at target. Twice-daily dosing if afternoon fatigue persists.

Mid-module checkpoint

Never use SR formulations of thyroid hormone

Sustained-release (SR) thyroid preparations impair absorption and produce inconsistent serum levels through the day. Nimbus does not use SR thyroid in any form (DTE, levothyroxine, or liothyronine). The same rule applies to progesterone. SR is reserved for melatonin and DHEA where the pharmacokinetic profile actually serves the indication.

TPO antibody testing — optional, not required

Many mainstream protocols routinely order TPO antibodies. The Nimbus position: TPO testing is optional. A positive TPO confirms Hashimoto's, but it does not change the treatment plan when symptoms plus Free T3 are already driving the dose. Order it when the differential matters for counselling (e.g., a young patient considering pregnancy) or when the patient asks; otherwise it is not part of the baseline panel.

Treatment-induced TSH suppression is NOT iatrogenic Graves' disease

This is the rule the model and the prescriber both need to internalize: a patient who is on titrated DTE with euthyroid Free T3, no palpitations, no tremor, no weight loss, no insomnia, and resolved symptoms is not in iatrogenic hyperthyroidism even if the TSH is suppressed. The classic risks attributed to TSH suppression in the literature — atrial fibrillation, bone loss, sudden cardiac death — derive from autoimmune thyrotoxicosis (Graves' disease) where Free T3 and Free T4 are both elevated and the patient is symptomatic. They do not transfer cleanly to symptom-optimal exogenous DTE dosing in which Free T3 is in range.

Documentation discipline — never document weight loss as the indication

Every thyroid hormone in the US carries the FDA Boxed Warning that thyroid hormones are not indicated for the treatment of obesity or weight loss and that larger doses may produce serious or life-threatening toxicity, particularly when given with sympathomimetic amines.^{[fda-thyroid-bbw]}

The documentation rule is therefore absolute: never record weight loss as the indication for thyroid replacement. If a patient mentions weight loss as the reason for asking, redirect: thyroid replacement is for symptomatic hypothyroid function documented by labs and clinical findings; for weight management we route to the GLP-1 / WeightWise tier with appropriate documentation. If the same patient also has documented hypothyroid symptoms with a low Free T3, document that indication separately and treat it on its own merits.

Role-specific operations

Cheat sheet — the numbers that drive the visit

Post-test — synthesis

Module evaluation