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1 results

  • Participant dropout and retention in a Phase 1 Clinical Studies Unit: A five-year retrospective analysis (2021–2025)

  • Paula Ferraz Oliveira, Sofia Luz Gouveia, Miguel Souto, Filipa Borges Carneiro, Beatriz Campos, Susana Paixão, Suzana Cecatto, Marlene Fonseca
  • Journal:
    Journal of Clinical and Translational Science / Volume 10 / Issue 1 / 2026
    Published online by Cambridge University Press:
    15 October 2026, e186
    • Article
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  • Introduction:

    Participant retention is a critical determinant of Phase 1 clinical trial validity. Published data on dropout and retention, specifically in Phase 1 healthy participant settings, remains limited.

    Methods:

    We conducted a retrospective observational analysis of all trials performed at a Phase 1 Clinical Studies Unit in Porto, Portugal, between January 2021 and December 2025.

    Results:

    Across 99 trials and 14,331 scheduled screening visits, 4,013 participants were enrolled. The study population was predominantly female, with a mean age of 32.9 years. The average post-randomization retention rate was 92.2%, improving progressively over the study period. The leading causes of post-randomization dropout were adverse events (AEs) (40.6%) and participant-initiated withdrawal (38.4%).

    Conclusions:

    This analysis demonstrates high and improving retention rates over five years, namely due to COVID-19 pandemic resolution, with AEs and participant-initiated withdrawal as the primary drivers of post-randomization dropout. These findings support unit-level retention tracking and highlight priority areas for operational improvement in Phase 1 research.