Hughes 1990.

Study characteristics
Methods	Study design: parallel RCT Country: USA Recruitment: community volunteers
Participants	78 smokers, motivated to quit 46% men, average age 34 to 44, average cigarettes per day 24 to 30
Interventions	1) Placebo gum 2) 1 mg nicotine gum (unbuffered formula, available dose approximately 0.5 mg) 3) 2 mg nicotine gum 4) 4 mg nicotine gum Gum use not recommended for longer than 3 months
Outcomes	Sustained abstinence at 6 months Validation: independent observer report Adverse events: measured at 1‐week follow‐up (within treatment) using a 13‐item side effects scale. Note: none of the side effects included in the scale are cardiovascular
Notes	This study was supported by Grants DA‐03728 and DA‐04066 and Research Scientist Development Award DA‐00109 (to JRH) from the National Institute on Drug Abuse. Merrell‐Dow Research Institute provided the drug for the study. Conflicts of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Subjects were randomly assigned"
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Quote: "in a double‐blind manner"; participants guessed to which group they had been assigned
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Subjects unable to be contacted were counted as smokers". Losses not reported