25 May 2021 - Randomised clinical trials allocate individuals to different treatments, or, more generally, to interventions and comparators, to determine whether one is better than another. 

However, after having been randomised to a given intervention, some study participants may not adhere to the assigned protocol. Treatment non-adherence may result from study participants crossing over to the other randomised treatments, taking non-trial medications, or not adhering to the study protocol. 

All of these situations introduce post-randomisation problems that may have to be accounted for in the analysis of data from the trial.

Read JAMA Guide to Statistics and Methods