Background: Case law across jurisdictions requires ever more complete disclosure of material facts when obtaining consent to treatment.
Aims: To determine whether giving extra information impairs the mental capacity to make decisions about treatment.
Method: The MacCAT-T, MacCAT-FP, PANSS and GAF were administered to 88 detained forensic patients with psychosis. Two positive and two negative facts were given about each of two anti-psychotic drugs, and no treatment (twelve items). A choice was elicited. The criterion for incompetence was inability to express a choice. Two extra positive and two extra negative facts about each of the three options were given (twelve extra items) and a choice was again elicited, while repeating the MacCAT-T.
Results: Giving extra information led to a decline in the total score on the MacCAT-T. Twenty one were initially unable to make a choice (24%). After additional information, 33 were incapable (37.5%, Chi-squared p<0.001). Those initially incapable had the lowest scores on all measures of functional capacity and GAF, with highest scores for symptoms. Those able to choose a treatment option had the highest levels of function and least symptoms. Those who became incapable had intermediate scores.
Conclusions: Giving extra information made an extra 15% unable to choose. Clinical judgement must be exercised concerning the amount of information disclosed. Deciding what is material to the individual is arbitrary when so few items of information can be processed. Greater use of guardianship and independent second opinions is recommended.