Urquhart 2018.

Study characteristics
Methods	Design: parallel Duration: 24 weeks Assessment: baseline, 3 months, post‐intervention Country: Australia
Participants	Pain condition: low back pain Population: people aged 18‐75 with chronic non‐specific low back pain Minimum pain intensity: no Inclusion criteria Aged 18–75 years with chronic, nonspecific low back pain lasted > 3 months Exclusion criteria Current physical or mental health comorbidities Previously diagnosed depression Total participants randomised: 146 Age in years (mean, SD): 54.8 (13.7) Gender: 53/146 were female Pain duration in years (mean): 14.3
Interventions	Placebo (benzotropine mesylate 1 mg) n = 74 Active placebo Identical appearance, matched dosing Amitriptyline 25 mg n = 72 TCA Fixed dose, no titration
Outcomes	Pain intensity Physical function Mood Quality of life AEs Withdrawal
Missing data methods	ITT using multiple imputation with chained equations
Funding source	Non‐pharmaceutical: "This work was supported by theNational Health and Medical Research Council(NHMRC, Australia, ID 1024401). Drs Urquhart, Wluka, and Wang are recipients of NHMRC Career Development Fellowships (Clinical Level 1 No.1011975; Clinical Level 2 No. 1063574; Clinical Level1 No. 1065464, respectively)"
Conflicts of interest	None reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Randomisation was based on computer‐generated random numbers prepared by a statistician who had no involvement in trial conduct."
Allocation concealment (selection bias)	Low risk	"The use of a central allocation that involved pharmacy‐controlled randomisation ensured that the allocation could not be accessed by research personnel."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind, active placebo, identical appearance, matched dosing
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Self‐reported outcomes by blinded participants
Incomplete outcome data (attrition bias) All outcomes	Low risk	Uses multiple imputation by chained equations, presents comparisons with no multiple imputation Attrition Total: 28/146 (19.2%) Placebo: 15/74 (20.3%) Amitriptyline 25 mg: 13/72 (18.1%)
Selective reporting (reporting bias)	Low risk	Matches protocol. Explains why Descriptor Differential Scale is NR (participants had difficulty filling it in)
Other bias	Low risk	No other sources of bias