Risk communication of study drug side effects: An evaluation of informed consent forms from ClinicalTrials.gov

Understandable safety language within informed consent forms (ICFs) is essential to informed clinical trial enrollment. Risk communication research has established that using the European Commission's (ECs) recommended verbal risk descriptors ('very common, common, uncommon, rare, and very rare') with a frequency band (e.g., 'may affect more than 1 in 10 people'), absolute frequency (e.g., '5 out of 100 participants'), or percentage (e.g., '5 %') is preferred, as it leads to improved comprehension of side effect susceptibility.

We aimed to examine how ICFs present study drug side effect information, including the use of EC recommended verbal risk descriptors.

We systematically assessed ICFs from clinical studies within ClinicalTrials.gov, to determine how side effect frequency was described. We evaluated the method used to describe the likelihood of side effects and the information's presentation.

547 English language ICFs were included in the analytic cohort. 104 ICFs (19 %) gave no indication of the frequency of study drug side effects occurring. 88 ICFs (16.1 %) used an EC recommended verbal descriptor with a frequency band, absolute frequency, or percentage, that displayed the incorrect probability of occurrence. Only 20 ICFs (3.6 %) used EC recommended verbal risk descriptors with their correct probability of occurrence. No ICFs utilized risk visualizations to display side effect frequency.

The communication of study drug side effects within ICFs varied widely and was often inadequate. The use of frequency bands, absolute frequencies, or percentages that incorrectly communicate the probability of occurrence associated with an EC verbal risk descriptor may exacerbate participant confusion on their susceptibility to risk.

This study highlights the need for standard guidance for side effect presentation within ICFs, which encourages the use of effective risk communication practices.