The cornerstone of hypothyroidism treatment — T4, T3, and NDT: how each works, clinical dosing, monitoring, and how to find a provider who actually tests Free T3.
Levothyroxine (T4) and liothyronine (T3) are the two active thyroid hormones used in hormone replacement. T4 is the long-lasting storage form; the body converts it to active T3 as needed. Natural desiccated thyroid (NDT) — Armour Thyroid, NP Thyroid — provides both, plus T2 and T1, from porcine thyroid glands.
All are prescription-only, FDA approved for hypothyroidism. Standard of care is T4-only replacement (Synthroid, levothyroxine). Patients who feel poorly on T4 alone may do better with combination T4+T3 or NDT — which typically requires finding a provider comfortable prescribing beyond the basic protocol.
FDA approved. Prescription only. Not WADA prohibited at replacement doses, but elevated exogenous thyroid use flagged in some sport contexts.
Levothyroxine (T4) is biologically inactive until deiodinated to T3 in peripheral tissues. Long half-life (~7 days) makes once-daily dosing feasible and stable.
Liothyronine (T3) is the biologically active hormone that binds nuclear thyroid receptors. Short half-life (~1 day) means dose fluctuations are felt more sharply. Some patients have impaired T4→T3 conversion (DIO2 polymorphisms) and do better with direct T3.
Desiccated porcine thyroid contains T4, T3, T2, T1 in a fixed ratio (~80:20 T4:T3). Natural ratio differs from human thyroid; some patients feel better on it, others don’t. Works well when baseline T4-only treatment leaves lingering symptoms.
| Benefit | Evidence |
|---|---|
| Hypothyroid symptom resolution | Gold-standard replacement; typically normalizes within 6–12 weeks of proper dosing |
| Energy & metabolism | Restored BMR and energy in hypothyroid patients |
| Cognitive function | Brain fog resolves with euthyroid restoration |
| Weight management | Resolves weight gain caused by hypothyroidism; not effective as a weight-loss drug in euthyroid patients |
| T4+T3 combo vs T4 alone | Mixed trials; ~10–20% of patients feel substantially better on combination therapy |
Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeTSH alone is insufficient. A proper panel includes:
Long-term over-replacement (suppressed TSH) increases risk of atrial fibrillation and bone density loss. "Optimizing" thyroid by running labs above range is not a free win.
Pre-filled with a typical Thyroid Hormones (T3 / T4) setup. Edit any field — the draw updates live.
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Thyroid Hormones (T3 / T4) is a prescription medication. StackTrax does not sell, prescribe, or facilitate purchase of prescription drugs.
Find a clinician who can order baseline lab work, screen for contraindications, monitor your response, and adjust dosing over time. Options to consider:
Before starting, you’ll typically want:
Avoid sources that offer prescription medications without labs, medical history, or licensed-provider oversight. If a telehealth service promises a prescription after a 5-minute questionnaire, that’s a red flag.
Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeT4 (levothyroxine) is the long-lasting pro-hormone — biologically inactive until the body deiodinates it to T3 in peripheral tissues. Its ~7-day half-life makes once-daily dosing stable. T3 (liothyronine) is the active hormone that actually binds nuclear thyroid receptors, with a much shorter ~1-day half-life so dose fluctuations are felt more sharply. Some patients have impaired T4-to-T3 conversion (DIO2 polymorphisms) and do better with direct T3.
Both are FDA approved for hypothyroidism. T4-only (Synthroid, levothyroxine) is the standard of care and works well for most patients. NDT (Armour, NP Thyroid) is desiccated porcine thyroid containing T4, T3, T2, and T1 in a fixed ~80:20 T4:T3 ratio. The natural ratio differs from human thyroid; some patients feel better on NDT, others don't. Mixed trials suggest about 10–20% of patients feel substantially better on combination therapy than T4 alone.
T3 (or NDT) is typically considered when baseline T4-only treatment leaves lingering symptoms despite normalized labs. Patients with impaired T4-to-T3 conversion (DIO2 polymorphisms) are the clearest candidates. Adding T3 requires a provider comfortable prescribing beyond the basic T4 protocol — typical T3 starting dose is 5–10 mcg/day split twice daily, titrated 5–10 mcg every 2–4 weeks.
No. TSH alone is insufficient for proper thyroid monitoring. A proper panel includes TSH, Free T4, Free T3, optionally Reverse T3 (useful if conversion issues are suspected), and thyroid antibodies (TPO, TgAb) at baseline for autoimmune screening.
It resolves the weight gain caused by hypothyroidism — but it is not effective as a weight-loss drug in euthyroid (normally functioning) patients. Long-term over-replacement with suppressed TSH increases risk of atrial fibrillation and bone density loss. Optimizing thyroid by running labs above range is not a free win.
Take it in the morning, 30–60 minutes before food, calcium, or iron. Standard starting dose is 25–50 mcg/day in elderly or cardiac patients, or 1.6 mcg/kg for full replacement. Titrate by 12.5–25 mcg every 6–8 weeks based on labs. Symptoms typically resolve within 6–12 weeks of proper dosing.
Elevated heart rate or palpitations, anxiety, irritability, tremor, heat intolerance, sweating, insomnia, unintended weight loss, and diarrhea. Long-term over-replacement (suppressed TSH) increases risk of atrial fibrillation and bone density loss, so these signs should prompt a dose reassessment rather than being pushed through.
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