Detailed definition
Steady state is the pharmacokinetic plateau where, with regular dosing, the rate of drug input matches the rate of elimination, and average plasma concentration is stable across dosing intervals. Time to steady state is determined by the drug's half-life: roughly 4–5 half-lives are required to reach approximately 95% of steady-state concentration. For transdermal estradiol with continuous release, steady state is reached within 1–2 days of patch application. For daily oral micronized progesterone, steady state is reached within a few days. Until steady state is reached, plasma levels are still rising; this is why some women notice continuing improvement over the first 2 weeks even at a fixed dose.
Why it matters in menopause
When patients ask "how soon will I feel different on HRT," the pharmacokinetic answer is: levels stabilize within days, but biological responses (cooling of vasomotor symptoms, restoration of vaginal tissue, mood changes) take additional weeks because they involve downstream tissue remodeling, not just hormone presence.
Related terms
Sources
External references: Wikipedia.