Shades of grey: The continuum of therapies for Parkinson's disease along the spectrum of credibility.

Complementary and alternative therapies (CAT) is an umbrella term applied to a diverse set of approaches, with high interest among persons with Parkinson's disease. However, scientific community regards evidence-based medicine as the only acceptable, creating a black and white dichotomy, which is neither epistemologically correct nor workable in daily practice. CAT are heterogeneous, and the label is dynamic as new scientific insights might accrue. Medicine encompasses a wide range of interventions that can be positioned alongside a spectrum of credibility, with many shades of grey between the extremes. We define credibility along three dimensions: the underlying rationale, the scientific rigor, and patient perceptions. By no means this implies we encourage adoption of weakly grounded therapies, or favor exotic treatments over evidence-based approaches. Credibility serves as basis for a nuanced debate in clinical practice, with attention to adverse effects, interactions, and costs. The degree of credibility also informs the need for further research. This offers a practical road forward for open-minded, yet rational decisions by persons with Parkinson's disease, clinicians, funding bodies and relevant stakeholders.