Introduction and aim: Medication adherence is one of the factors impacting drug efficacy in registration trials. We aimed to assess how medication adherence (both implementation and persistence) is addressed in registration studies for new medicines in Europe.

Methods: A quantitative cross-sectional analysis of European Medicines Agency (EMA) marketing authorisation dossiers for new medicines approved through centralised procedures in the EU between 2010 and 2020 was performed. Data were extracted from EPARs and from Clinical Study Reports. Pivotal efficacy studies in these dossiers were selected for five therapeutic areas: respiratory conditions, diabetes, oncology, cardiovascular diseases and anti-infectives. Treatments with indicated use period of at least 3 months to lifelong (chronic) were included. Outcomes included adherence measurement, method, and rates.

Results: For this interim report (date: 11/6/2021; anticipated full analysis completed: 29/8/2021), 89 medicines and 206 pivotal efficacy studies were reviewed. 98% of the trials measured adherence. The most common measurement method used was pill count, used by 80% of the trials. Other main methods used were patient diary/report forms (15%) and questionnaires (1%). 72 Studies used multiple methods to verify adherence (including blood samples). Overall adherence rates were over 90%.

Discussion: Overall, adherence is measured in EMA registration trials, yet the methods used and the way in which adherence rates are presented varies between trials.

Conclusion: The way adherence is addressed in EMA registration trials varies between medicinal products. More standardization on definitions and measurement methods seems required.