Longitudinal consent-related abilities among research participants with schizophrenia: results from the CATIE study

Research participants must have adequate consent-related abilities to provide informed consent at the time of study enrollment. We sought to determine if research participants with schizophrenia maintain adequate consent-related abilities during a longitudinal study. If participants lose abilities during a trial they may not be able to judge and protect their interests. If reduced abilities are common or can be predicted, special protections can be targeted appropriately.

We examined longitudinal consent-related abilities of participants in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) schizophrenia study using the MacArthur Competence Assessment Tool-Clinical Research (MacCAT-CR) at protocol-specified times over 18 months.

Of 1158 research participants in this analysis, most (n=650, 56%) had a stable pattern of MacCAT-CR Understanding scores, 235 (20%) improved substantially with no evidence of decline, 273 (24%) had at least one assessment with substantial worsening. During the course of the trial, 43 (4%) fell below the initial threshold for adequate capacity, which was predicted by lower Understanding scores, more severe positive symptoms, and poorer neurocognitive functioning at baseline, and by increases in negative symptoms and deteriorating global status.

Most participants in this long-term study had stable or improved consent-related abilities, but almost one-fourth experienced substantial worsening and 4% of participants fell below the study's capacity threshold for enrollment. Clinical investigators should monitor with special care individuals with marginal capacity or higher levels of psychotic symptoms at study entry and those who exhibit clinical worsening during a study.