Premature termination of clinical trials in Spain: reasons, characteristics, and opportunities to improve.

Purpose: The aim of this study is to determine the rate of prematurely terminated clinical trials (CTs) and describe primary reasons and characteristics, and suggest strategies to improve.

Methods: We performed a retrospective, observational, cross-sectional study including all CTs registered in the Spanish Registry of Clinical Studies (REec) from January 1, 2013 to November 31, 2021. A descriptive analysis of reasons for premature termination was made.