Levothyroxine

Synthroid · Levoxyl · Euthyrox · Tirosint

Other GLP-1 TRT HRT Oral FDA/EMA Label

Half-life

7 days

Time to Peak

3 hr

Steady State

~35 days

Bioavailability

80%

Dose Range

25–300 mcg

Frequency

once daily

Overview

Synthetic T4 (thyroxine) — the most prescribed thyroid medication globally. Very long half-life means missed doses are less critical but takes 4-6 weeks to reach steady state. Must be taken on an empty stomach for proper absorption.

Mechanism of Action

Synthetic L-thyroxine (T4), a prohormone that is converted to active T3 (triiodothyronine) by deiodinase enzymes in peripheral tissues. Replaces deficient endogenous thyroid hormone.

Dosing Information

Route	Dose Range	Half-life	Tmax	Frequency
Oral	25–300 mcg	7 days	3 hr	once daily

Used in Regimens

Levothyroxine is not currently part of any catalog regimen.

Data Sources

FDA Label Synthroid (levothyroxine) FDA Prescribing Information

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