T3/T4 Thyroid Blend Dosage Guide: Protocols, Calculator & Safety

There is no safe 'beginner' self-start for thyroid hormone. Thyroid hormones are not supplements - they are potent prescription drugs with a narrow therapeutic window. The only appropriate first step is diagnostic, not pharmacologic: a clinician-ordered thyroid panel (TSH, free T4, and often free T3 and TPO antibodies) to confirm whether a real deficiency exists. Thyroid symptoms (fatigue, weight change, brain fog) overlap with dozens of other conditions, and dosing thyroid hormone into a normal thyroid causes harm, not benefit. If replacement is genuinely indicated, standard practice starts with levothyroxine (T4) alone - not a T3/T4 blend - at a physician-calculated, weight-based dose, with labs rechecked in 6-8 weeks before any change [PMID:25266247]. Adding T3 is a second-line specialist decision, never a starting point.

'Intermediate' here means physician-supervised combination therapy in a diagnosed, already-treated hypothyroid patient who remains symptomatic on levothyroxine despite a normal TSH - the only population where a T3/T4 approach is even reasonable [PMID:33276704]. In that supervised setting, clinicians typically keep the levothyroxine (T4) dose the same or slightly reduced and add a SMALL amount of liothyronine (T3), aiming to approximate the roughly 13-14:1 T4:T3 ratio of native thyroid secretion - not the roughly 4:1 ratio of desiccated extract, which over-delivers T3. Because liothyronine is short-acting, it is split into two or more daily doses (or a slow-release form is used) to avoid post-dose T3 spikes [PMID:37738506]. TSH, free T4 and free T3 are rechecked and the dose is titrated to keep all in range. This is a titration-to-labs process run by a prescriber, not a fixed self-administered 'stack.'

There is no legitimate 'advanced' recreational or performance protocol for a T3/T4 blend. The main gray-market users are physique/bodybuilding communities using T3 (sometimes with T4) to accelerate fat loss - a practice that deliberately induces thyrotoxicosis and is genuinely dangerous: it drives muscle-protein loss alongside fat, tachycardia and atrial fibrillation, cardiac hypertrophy, and accelerated bone loss with higher fracture risk, and abrupt discontinuation can leave the person transiently hypothyroid while the HPT axis recovers [PMID:26010634] [PMID:22561612] [PMID:33543160]. None of this is endorsed here. The genuinely advanced version of this topic is medical: a thyroidologist managing a difficult-to-treat patient (e.g., a suspected under-converter, post-thyroidectomy, or someone in a monitored trial of slow-release T3), always with lab surveillance and cardiac/bone risk assessment [PMID:33276704].