This is the part of ECT people find most uncomfortable, and it deserves a straight answer rather than avoidance.
Some people become so unwell that they cannot weigh up a treatment decision — a state clinicians describe as lacking capacity. Researchers at a single centre compared outcomes for 175 patients receiving ECT for schizophrenia, depression or mania. Notably, 75.1% of them lacked capacity to consent at the time.
Before treatment, that group had poorer thinking and general functioning. After ECT, symptom ratings improved similarly across both groups. Mood, thinking, quality of life and day-to-day functioning all improved in both — with greater gains in mood and functioning among those who had lacked capacity.
The authors are careful about the limits: thinking was measured with a general screening tool rather than full neuropsychological testing, and the groups were too small to break down by diagnosis.
What this offers is some reassurance about a genuinely difficult situation. Families sometimes have to be involved in decisions for someone too unwell to make them, and this suggests that people treated in those circumstances do improve — including in the abilities that let them make their own decisions again.