Run-In Period
A pre-treatment phase at the beginning of a clinical trial during which all participants may receive placebo or standardised care. Run-in periods help stabilise baseline measurements, identify non-compliant participants, and wash out effects of previous medications.
Technical Context
Run-in period purposes: establish stable baseline measurements (reducing variability), identify and exclude non-compliant participants (improving adherence in the randomised phase), wash out effects of prior medications, and standardise background therapy. Placebo run-in (all participants receive placebo) identifies strong placebo responders who can be excluded, enriching the randomised population for drug-responsive patients. Active run-in (all participants receive active treatment) identifies intolerant patients before randomisation, reducing post-randomisation dropout. Run-in periods can bias trials — enrichment designs may overestimate the drug's benefit in the general population by excluding non-responders and non-tolerators.