Capacity-related exclusions in clinical trial protocols are common, with limited assessment and almost no planning for capacity loss.

BACKGROUND: People who are assumed to have impaired decision-making capacity continue to be under-served in clinical research, despite legislation aimed at supporting their inclusion. Previous studies have highlighted the routine exclusion of individuals with intellectual disabilities or cognitive impairments, but little is known about how capacity-related decisions are documented at the protocol stage. This study examines how clinical trial protocols describe the inclusion or exclusion of individuals with impaired capacity, the assessment of capacity, and any plans for participants who might lose capacity during a trial. METHODS: A structured content analysis was conducted on 500 clinical trial protocols selected from a larger dataset of 824 protocols previously identified for another study. Protocols were screened in reverse chronological order until the target number was reached. Extraction focused on capacity-related eligibility criteria, who conducted capacity assessments, any mention of training of assessors, and procedures for participants who might lose capacity. Descriptive statistics were used to summarise findings. RESULTS: Of the 500 trial protocols reviewed, 214 (43%) made direct eligibility decisions based on decision-making capacity, and a further 92 (18%) referenced capacity indirectly through informed consent requirements, totalling 306 protocols (61%) with capacity-related criteria. Only 53 protocols (53/306, 17%) described how capacity would be assessed, 28 of these 53 identified who would conduct the assessment, and just two mentioned any assessor training. Most assessors were non-clinical staff. Just three protocols (1%) included plans for participants who might lose capacity during the study. CONCLUSIONS: This study demonstrates that capacity-related exclusions are common in clinical trial protocols, yet the processes behind these decisions are poorly documented. The lack of detail regarding assessors, training, and loss-of-capacity planning raises concerns about transparency and inclusion. Strengthening transparency and guidance at the protocol stage could help ensure that individuals with impaired or fluctuating capacity are not unethically or systematically excluded from research. PLAIN LANGUAGE SUMMARY: Are people who find it hard to make decisions left out of clinical trials?. Clinical trials are studies that test new treatments. Some people find it harder to make decisions about things like their health. This might be because of a learning disability or a condition that affects their thinking. Laws say these people should be able to join clinical trials too. But research shows they are often left out. We wanted to know more. We looked at the written plans for clinical trials, called "protocols." We wanted to see what these plans said about including or excluding (leaving out) people who find decision-making hard. We also wanted to see how researchers planned to check if someone could make their own decisions.