Unpacking the 'black box of horrendousness': a qualitative exploration of the barriers and facilitators to conducting trials involving adults lacking capacity to consent.

Researchers encountered a number of barriers, including both generic and context or population-specific challenges, which may be reinforced by wider factors such as resource limitations and knowledge deficits. Greater access to expertise and training, and the development of supportive interventions and tailored guidance, is urgently needed in order to build research capacity in this area and facilitate the successful delivery of trials involving this under-served population.