This paper reports on exploratory, qualitative research conducted with eight people with experience of mental health treatment about their understanding of decision-making capacity. While acknowledging that there are times when mental or emotional distress can interfere with the capacity to make decisions, participants described how their capacity can be reduced by a set of social and environmental factors. These factors include the lack of treatment options available from which to choose, lack of trust of the information provider, inaccessible information, the effects of medication that literally "stops your ability to think", lack of empathy with mental or emotional distress, and lack of time to process information. Participants highlighted the issue of power and powerlessness when describing how incapacity is determined within mental health services. Participants' articulations of capacity in relation to mental health are in accord with a social model of disability approach to capacity. (Contains 1 note.)