Thyroid T3/T4 (Liothyronine / Levothyroxine)
T4 (levothyroxine) is the predominant circulating thyroid hormone, converted peripherally to the active T3 (liothyronine) form via deiodinase enzymes. T3 binds nuclear thyroid receptors, regulating basal metabolic rate, mitochondrial thermogenesis, protein synthesis, and lipid metabolism. Controls gene expression across virtually every tissue through thyroid response elements on DNA.
Three tiers ordered by aggressiveness. Tier chips on every OPTIMIZE intervention let you filter the catalog by your evidence tolerance.
- thyroid-panel
- total-testosterone
- free-testosterone
- shbg
- lipid-panel
- fasting-glucose
- hba1c
- cortisol
- iron-panel
- vitamin-d
- thyrotoxicosis
- untreated-adrenal-insufficiency
- acute-myocardial-infarction
- uncorrected-adrenal-insufficiency
- PMID:24297018Guidelines for the treatment of hypothyroidism — Thyroid, 2014
- PMID:27521067Thyroid hormones and their clinical significance — Ann Thyroid Res, 2016
- PMID:288597092017 ATA guidelines for thyroid disease in pregnancy — Thyroid, 2017
- PMID:31365801Combination therapy with levothyroxine and liothyronine — Front Endocrinol, 2019
Thyroid is the metabolic thermostat. Every system downstream — testosterone production, lipid clearance, glucose metabolism, even mood — depends on this axis functioning. The T4 to T3 conversion ratio is where most clinicians stop and most patients suffer. A TSH of 3.5 is normal on the lab range. It is not optimal. The deiodinase enzymes that convert T4 to T3 are selenium-dependent, stress-sensitive, and inflammation-modulated. You cannot optimize thyroid by reading one number on a lab report. Free T3, reverse T3, the ratio between them — that is where the signal lives.
This is not medical advice
Discuss with a licensed clinician before starting, stopping, or changing any compound. This page documents what the research literature describes — it is not a prescription.
See Thyroid T3/T4 (Liothyronine / Levothyroxine) in a protocol matched to you