Half-life sets how fast a hormone signal fades
A hormone's half-life is the time for its blood concentration to fall by half once secretion stops. It spans an enormous range. Catecholamine-adjacent and steroid signals like cortisol clear in roughly one to two hours, and testosterone is often cited in the tens of minutes range, while estradiol persists longer at around half a day. Thyroid hormone thyroxine (T4) is the slow extreme, with a half-life on the order of a week.
Exact figures vary with binding proteins, measurement method, and the source, so these are typical orders of magnitude rather than fixed constants.
Why the range has practical consequences
Short half-lives let a hormone start and stop a response quickly, which suits fast regulators of stress and fuel. Long half-lives buffer a signal so it stays steady, which suits thyroxine's role in setting baseline metabolic rate. The contrast also explains why some hormones are dosed once daily while others need frequent measurement.
This is general educational information, not medical advice; dosing and timing decisions for any hormone therapy must be made with a qualified professional.