Levothyroxine
Approved, for something elseHeight measured in peopleBy mouthHormoneAlso T4
The standard thyroid tablet, licensed from birth, which the body converts into the active hormone inside its own cells.
Standard thyroid hormone replacement, approved down to neonates for congenital hypothyroidism. T4 is the prohormone: conversion to active T3 happens inside the cell, by deiodinases, so the tissue sets its own T3 exposure rather than taking what the blood offers.
Risks. Its label carries a boxed warning that it does nothing for someone whose thyroid already works, and that taking more than a replacement amount is dangerous.
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Educational content, not medical advice. Nothing here is a recommendation to take or stop taking anything — talk to a doctor about your own situation.