Objectives To assess how and to what extent adherence to medication is reported in pivotal clinical trials of oral cancer drugs.

Methods All drugs authorised by the European Medicines Agency from 1 January 2014 to 31 December 2019 were considered for analysis. For each pivotal trial we extracted the journal of publication, phase of the study, posology, mention of adherence within the main text of the published article or additional material and the terms in which the adherence was reported.

Results Thirty drugs were included in the analysis from 56 clinical trials. Eleven articles (19.6%) contained a mention of medication adherence in the main document, 26 (46.4%) in the supplementary material and 19 (33.9%) did not contain any reference to adherence. Seven studies reported medication adherence between the results, expressed as number of patients discontinuing treatment for non-compliance and mean or median percentage.

Conclusions Medication adherence in pivotal clinical trials of oral oncological drugs is poorly represented. There should be a greater level of reporting in the results and it should be included among the minimum set of recommendations in reporting health research.