Purpose
Medication adherence is a multi-faceted construct associated with several positive consequences in people with chronic conditions. However, non-adherence currently represents a major issue in Parkinson’s, potentially due to low perceptions of control. This study investigated the predictive ability of several aspects of perceived control on adherence in people with Parkinson’s, while accounting for previously established predictors such as depression and medication variables.

Materials and Methods
An online cross-sectional survey was carried out with 1210 adults with Parkinson’s from 15 English-speaking countries. Demographic and clinical questions, as well as measures of depression, aspects of perceived control, and medication adherence were included. Pearson’s correlations and a 4-block hierarchical regression analysis were performed to assess the relationship between the variables.

Results
Perceived control explained a slightly higher amount of variance in medication adherence compared to medication variables when entered in the last block. Unexpectedly, depression was not significantly related with adherence. Internal locus of control was an independent negative predictor of adherence, while external dimensions of locus of control emerged as independent positive predictors.

Conclusions
In people with Parkinson’s, perceptions of control may have a larger impact on adherence compared to medication variables. Implications for clinical practice and future research are discussed.

Implications for Rehabilitation
Perceived control and depression are considered important constructs for medication adherence in Parkinson’s, which in turn is often problematic for affected individuals.

The specific predictive value of different aspects of perceived control on medication adherence in Parkinson’s is currently unclear.

This large-scale study found that perceptions of control may have a larger impact on adherence compared to medication variables, while depression was unrelated to it.

A need for psychologically-informed interventions, person-centred approaches to medication management, and Parkinson-specific measures of adherence are highlighted.