Capacity of persons with mental retardation to consent to participate in randomized clinical trials

Adults with mental retardation have histories of cognitive and adaptive deficits posing unique ethical challenges for research consent assessment. This study examined the capacity of persons with mental retardation to consent to participate in randomized clinical trials.

A total of 150 adults (50 each with mild and moderate mental retardation and 50 comparison subjects without mental retardation) responded to a set of consent questions for a hypothetical randomized clinical trial testing a medication for aggressive disorders. Intelligence, adaptive behavior, medical treatment history, and consent history were evaluated. Univariate and multivariate methods were used to compare performance across and within groups.

Comparison subjects scored significantly higher on measures of consent capacity than participants with mild mental retardation, who scored higher than those with moderate mental retardation. Most subjects with mental retardation were able to make a participation choice, and many understood research methods and appreciated the protagonist's disorder and the consequences of participation. Almost half of those with mild mental retardation understood human subject protections. Performance was weakest on understanding the purpose of research and reasoning about whether to participate, suggesting vulnerability to the therapeutic misconception. Psychiatric and experiential factors did not predict consent capacity.

While adults with mental retardation as a group showed consent deficits, many attained consent capacity scores comparable to those of comparison subjects. Investigators should consider individual differences and a consent format suited to deficits in language, memory, and attention before restricting consent opportunities for persons with mental retardation.