Bjørkedal 2011.

Study characteristics
Methods	Type: preclinical Design: 4‐period cross‐over and 2 × 2 factorial design (balanced placebo design), as follows.  Standard placebo, participants told it was a placebo Standard placebo, participants told it was a painkiller Active placebo, participants told it was a placebo Active placebo, participants told it was a painkiller For analysis, we combined 1 with 2 (all standard placebo groups) and 3 with 4 (all active placebo groups). Objective: to test whether side effects of drugs (atropine) can enhance expectancies and placebo responses Treatment duration: instant (single oral dose) Follow‐up duration (including treatment duration): 30 minutes per period Washout between cross‐over periods: minimum 24 hours
Data	Country: Norway Condition: experimental laser‐induced heat pain Number of people randomised: 23 (to a sequence of 4 interventions, i.e. 92 units). Number of people analysed: 20 (80 units), as 3 subjects did not find the stimulus painful.
Comparisons	Active placebo: caffeine (4 mg/kg) in grapefruit juice Standard placebo: grapefruit juice Experimental intervention: no matched experimental treatment. However, placebo intervention supplied with information explaining it was a placebo or a painkiller. Administration: oral
Outcomes	Participant‐reported outcome: pain on NRS of 0–10, assessed at 30 minutes Observer‐reported outcome: laser‐evoked potentials with EEG recordings, including N2 and P2 amplitudes and latencies, assessed at 30 minutes Harm outcome: none Co‐intervention outcome: none
Terminology for active placebo	"Active placebo" a priori. However, in some cases the trial authors also refer to"active placebo" as the combination of active placebo drug with information that they are receiving a painkiller (group 4).
Scores and unpleasantness of the active placebo	Adequacy: NA Risk of therapeutic effect: 2 Unpleasant/neutral/pleasant: unpleasant
Funding and conflicts of interest	No industry funding. Trial authors declared no conflicts of interest.
Notes	Access to individual participant data with 20 measurements for each participant for each intervention
Risk of bias
Item	Authors' judgement	Support for judgement
Free from risk of bias arising from the randomisation process	Yes	Information from trial author: random draw of sealed, opaque envelopes containing an ID. Remote telephone contact with trial author who matched the ID with sequence. 23/24 possible treatment sequences used.
Free from risk of bias in selection of the reported result All outcomes	Yes	Trial author provided access to all study data.