No decision about me without me? Shared decision-making in mental healthcare.

Is there really 'no decision about me without me'? This concept of shared decision-making is increasingly supported in the UK National Health Service and is to be welcomed. But the attempt to apply guidelines based on Western physical health settings to all psychiatric patients, across different cultural backgrounds, is problematic. Methodological difficulties when trying to apply the gold standard of randomised controlled trials to the real-life settings of mental health should be considered, especially when many patients with serious mental health problems are excluded, having been deemed to 'lack capacity'. Should guidelines originating in physical healthcare settings really be applied to mental health ones? Does one size really fit all?