Background
Electronic monitoring is recommended for accurate measurement of medication adherence but a possible limitation is that it may influence adherence.

Purpose
To test the reactive effect of electronic monitoring in a randomized controlled trial.

Methods
A total of 226 adults with type 2 diabetes and HbA1c ≥58 mmol/mol were randomized to receiving their main oral glucose lowering medication in electronic containers or standard packaging. The primary outcomes were self-reported adherence measured with the MARS (Medication Adherence Report Scale; range 5–25) and HbA1c at 8 weeks.

Results
Non-significantly higher adherence and lower HbA1c were observed in the electronic container group (differences in means, adjusting for baseline value: MARS, 0.4 [95 % CI −0.1 to 0.8, p = 0.11]; HbA1c (mmol/mol), −1.02 [−2.73 to 0.71, p = 0.25]).

Conclusions
Electronic containers may lead to a small increase in adherence but this potential limitation is outweighed by their advantages. Our findings support electronic monitoring as the method of choice in research on medication adherence. (Trial registration Current Controlled Trials ISRCT N30522359)