Shader 1964.

Study characteristics
Methods	Type: preclinical Design: cross‐over Objective: to find an active control substance that could later be used in a psychotic population under double‐blind conditions with an effective phenothiazine Treatment duration: 4 days per cross‐over period Follow‐up duration (including treatment duration): 4 days per cross‐over period Washout between cross‐over periods: 9 days
Data	Country: USA Condition: psychiatric symptoms in healthy participants Number of people randomised: 20 Number of people analysed: 20 in each placebo group
Comparisons	Active placebo: phenobarbital (50 mg) and atropine sulphate (0.3 mg) 4 times daily Standard placebo: lactose Experimental intervention: none Administration: oral
Outcomes	Participant‐reported outcome: Revised Clyde Mood Scale (self‐sort) Observer‐reported outcome: Revised Clyde Mood Scale (observer‐sort) Harm outcome: symptoms and side effects questionnaire Co‐intervention outcome: none
Terminology for active placebo	"Active control" a priori (also uses the term "active placebo" elsewhere in the introduction)
Scores and unpleasantness of the active placebo	Adequacy: 3 Risk of therapeutic effect: 1 Unpleasant/neutral/pleasant: unpleasant
Funding and conflicts of interest	Non‐industry funding. Conflicts of interest not reported.
Notes	This is a 2‐phase study; we were only interested in phase I.
Risk of bias
Item	Authors' judgement	Support for judgement
Free from risk of bias arising from the randomisation process	Unclear	No information.
Free from risk of bias in selection of the reported result All outcomes	Unclear	No information.