Implications for practice 

• There is no moderate‐ or high‐quality data that any intervention tested reduces weight gain in the long term.
• There is low‐certainty evidence that weight‐management education may reduce abstinence and is not effective at controlling weight.
• There is low‐ to very low‐certainty evidence that personalized weight‐management support programmes, incorporating both feedback on personal goals and a personal energy prescription, may reduce weight gain. There is mixed and low‐certainty evidence of their effects on abstinence.
• Very low calorie diets may increase abstinence and prevent weight gain in the short term at least, but these conclusions are based on a single trial only, and another small trial found no one adhered to the intervention.
• There was low‐ to very low‐certainty evidence that interventions designed to allay concerns about weight gain did not meaningfully affect weight gain but low certainty that they increase abstinence.
• There was low‐certainty evidence that exercise interventions for smoking cessation did not affect weight by the end of treatment, so the 12‐month reduction in weight is unexplained.
• Nicotine replacement therapy, bupropion, fluoxetine and varenicline all slightly reduced weight gain in the short term, but the size of benefit, if any, at 12 months was very uncertain, and evidence suggests was modest at best.  

Implications for research 

• As none of the existing pharmacotherapies tested to limit weight gain appear promising, testing newer agents now licensed for weight control to prevent weight gain may be helpful. Studies could also explore combining behavioural support and pharmacotherapy.
• Fluoxetine for smoking cessation was associated with reduced weight gain at end of treatment and six months, but evidence was very uncertain. Further studies are needed, particularly following up participants at six months and beyond.
• Behavioural weight management programmes are the mainstay of treatment for weight management and further trials to assess the impact of programmes tailored to people's concerns about weight gain would clarify the evidence on whether they limit long‐term weight gain and their impact on abstinence from smoking.
• Further studies of interventions to allay people's concerns about weight gain are required to clarify its effect on smoking cessation.
• Further studies of exercise interventions are needed. The finding that an intervention aimed at increasing exercise levels had no effect initially but somehow affected weight one year later seems counterintuitive, as adherence to exercise regimens usually declines rather than increases with time.
• Future trials of interventions for limiting post‐cessation weight gain should report mean weight change, standard deviation for the weight change and the number contributing to the mean in biochemically‐confirmed continuous or prolonged abstinent participants only rather than in those abstinent for only one week. Weight change in those who continue to smoke should be reported separately.
• Trials of current and future pharmacotherapies for smoking cessation should measure weight change, reporting mean weight change, standard deviation of the change and numbers contributing to the mean, separating abstinent from smoking participants as described above. 
• Future studies could also report results separately in those with overweight or obesity at baseline, or focus on recruiting from this population.
• Data are needed on whether using e‐cigarettes to quit smoking affects post‐cessation weight change.