A Cochrane review included 24 trials about interventions to help smokers cut down the amount smoked. Most trials tested nicotine replacement therapy (NRT) to assist reduction. In a pooled analysis of 8 trials, NRT significantly increased the odds of reducing cigarettes per day (CPD) by 50% or more for people using nicotine gum or inhaler or a choice of product compared to placebo (RR 1.75, 95% CI 1.44 to 2.13, n=3 081). Where average changes from baseline were compared for different measures, CO and cotinine consistently showed smaller reductions than CPD. Small numbers of smokers in either treatment or control group successfully sustained a reduction of 50% or more. Use of NRT increased the odds of quitting (RR 1.73, 95% CI 1.36 to 2.19). Only one trial investigated each of the following harm reduction intervention aids: bupropion, varenicline, electronic cigarettes, snus, plus another of nicotine patches to facilitate temporary abstinence. The evidence for all five intervention was therefore imprecise.
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment) and by inconsistency (heterogeneity in interventions and outcomes). The authors of the review state that because the long-term health benefit of a reduction in smoking rate is unclear this application of NRT is more appropriately used as a precursor to quitting.