Wang 2008a.

Study characteristics
Methods	Type: preclinical Design: cross‐over Objective: to determine whether pregabalin and morphine could inhibit secondary hyperalgesia and allodynia induced by ID capsaicin compared with the active placebo diphenhydramine hydrochloride and true placebo; and to evaluate the value of diphenhydramine as a control. Treatment duration: instant (single dose) Follow‐up duration (including treatment duration): 240 minutes from capsaicin; 265 minutes from randomised IV treatment/315 minutes from randomised oral treatment; 330 minutes from first assessment; per cross‐over period (separate days) Washout between cross‐over periods: crossover periods were on separate days, no further information
Data	Country: USA (presumably) Condition: experimental capsaicin‐induced pain Number of people randomised: 20 Number of people analysed: 20 for each placebo type
Comparisons	Active placebo: diphenhydramine hydrochloride (50 mg) Standard placebo: not described Experimental intervention: 2 groups: pregabalin (300 mg) and morphine (10 mg) Administration: oral (except IV morphine)
Outcomes	Participant‐reported outcome: area of hyperalgesia Observer‐reported outcome: area of flare Harm outcome: none Co‐intervention outcome: none
Terminology for active placebo	"Active placebo" a priori
Scores and unpleasantness of the active placebo	Adequacy: 3 Risk of therapeutic effect: 2 Unpleasant/neutral/pleasant: unpleasant
Funding and conflicts of interest	Industry funded. All trial authors had conflicts of interest.
Notes
Risk of bias
Item	Authors' judgement	Support for judgement
Free from risk of bias arising from the randomisation process	Yes	Computer‐generated allocation schedule. Described as blinded to investigators and participants. Probably concealment of allocation
Free from risk of bias in selection of the reported result All outcomes	Unclear	No information.