placebo lead-in
Pre-randomization period where all participants receive placebo to identify and exclude placebo responders.
Full Definition
A placebo lead-in is a study design feature consisting of a pre-randomization period during which all participants receive placebo treatment for a specified duration, typically 1-4 weeks. The primary purpose is to identify and exclude participants who show significant improvement on placebo alone (placebo responders) before randomization to active treatment or placebo. This approach aims to reduce placebo response rates in the subsequent randomized phase and increase assay sensitivity. In psychiatric research, placebo lead-ins are controversial because they may select for treatment-resistant patients and raise ethical concerns about prolonging patient suffering. Modern psychiatric trials often avoid this design in favor of other enrichment strategies.
Usage
Usage note: Hyphenate when used as compound modifier: 'placebo-lead-in period'.
In Context
- "The two-week placebo lead-in excluded 15% of enrolled participants who showed early response." — Clinical trial design manuscript
- "Modern depression trials typically avoid placebo lead-in designs due to ethical considerations." — Regulatory guidance document