4. Suggested design for future study.

Methods	Allocation: randomised, clearly described. Blinding: double, tested. Duration: 1 week. Need short‐, medium‐ and long‐term follow‐up.
Participants	Diagnosis: people at ultra‐high risk of developing psychosis. N = 300.* Age: young adults. Sex: male only (due to mifepristone interaction with progesterone receptor). History: demonstrable HPA axis hyperactivity.
Intervention	1. Mifepristone: flexible dose 400 to 600 mg/day. N = 150. 2. Placebo. N = 150.
Outcomes	Global state: relapse, time to transition to psychosis. Service outcomes: admission, time in hospital. Mental state: CGI, Total psychotic (BPRS) and depressive symptoms. General functioning: quality of life measures. Neuroendocrine measurements: cortisol awakening response and circadian rhythm measured on 2 consecutive days.
Notes	*Powered to be able to identify a difference of ˜ 20% between groups for primary outcome with adequate degree of certainty.