Tønnesen 1988.

Study characteristics
Methods	Study design: parallel RCT Country: Denmark Recruitment: primary care
Participants	113 low‐ to medium‐dependence smokers, motivated to quit (19 or less on Horn‐Russell scale) 44% men, average age 45, average cigarettes per day 20 60 highly‐dependent smokers 42% men, average age 45, average cigarettes per day 26 to 28
Interventions	Group A: low/medium dependence 1) Nicotine Gum (2 mg) for 16 weeks 2) Placebo Group B: high‐dependence 1) Nicotine gum 4 mg for 6 weeks then 2 mg 2) Nicotine gum 2 mg
Outcomes	Sustained abstinence at 12 months (24 months also reported) Validation: CO Adverse events: measured during counselling sessions to end of treatment (either 16 or 20 weeks)
Notes	"This study was supported in part by a grant from the Danish National Tuberculosis Foundation. A.B. Leo, Halsingborg, Sweden and H. Lundbeck A.S., Denmark supplied the nicotine and placebo chewing gum". Conflicts of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Participants stratified by dependence, then [quote]: "subjects on each list were then randomly assigned to treatment in blocks of two"
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Gum was packaged and produced to be indistinguishable between 2 mg, 4 mg and placebo
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants who attended 1st counselling session were included in analyses, regardless of attendance or level of gum use Only 2/173 were lost to follow‐up