People who smoke may be unwilling or unable to stop smoking completely. Cutting down the number of cigarettes smoked daily or smoking less damaging products may reduce the harm caused by smoking. It may also be a step towards stopping smoking completely. This approach might, however, undermine the importance of quitting which has very clear health benefits. We found 16 controlled trials that tested ways to help people to cut down the number of cigarettes they smoked. We found three randomized controlled trials which tested the effects of using products designed to reduce damage, such as Potentially Reduced Exposure tobacco Products (PREPs). Eleven of the trials tested nicotine replacement therapy (NRT) as an aid to cutting down. Our combined analysis of nine of these trials (3429 smokers) found that nicotine replacement roughly doubled the odds of reducing the number of cigarettes per day by 50% or more. However, levels of carbon monoxide and cotinine (markers within the body of exposure to tobacco smoke) did not reduce by the same proportion. This suggested that there may not be a direct relationship between the reduction in number of cigarettes and the reduction in harmful effects. Although NRT helped significantly more people to cut down, few were able to sustain the reduction over time. NRT also nearly doubled the odds of quitting completely. One trial failed to find a benefit of bupropion either for cutting down or for quitting. Four trials tested advice or instructions for reducing the number of cigarettes smoked per day, and did not find clear evidence of a significant effect. We did not find any trials which reported the long-term effects on health of cutting down, and it remains uncertain how much health benefit there is from cutting down.
There is insufficient evidence about long-term benefit to support the use of interventions intended to help smokers reduce but not quit smoked tobacco use. Some people who do not wish to quit can be helped to cut down the number of cigarettes smoked and reduce their CO levels by using nicotine gum or nicotine inhaler. Because the long-term health benefit of a reduction in smoking rate is unclear, but is likely to be small, this application of NRT is more appropriately used as a precursor to quitting.
It may be reasonable to try to reduce the harm from continued tobacco use amongst smokers unable or unwilling to quit. Possible approaches to reduce the exposure to toxins from smoking include reducing the amount of tobacco used, and using less toxic products. The interventions evaluated in controlled trials have predominantly attempted to reduce the number of cigarettes smoked.
To assess the effect of interventions intended to reduce the harm from smoking on the following: biomarkers of damage caused by tobacco, biomarkers of tobacco exposure, number of cigarettes smoked, quitting, and long-term health status.
We searched the Cochrane Tobacco Addiction Group Specialised Register in June 2010 using free text and MeSH terms for harm reduction, smoking reduction and cigarette reduction.
Randomized or quasi-randomized controlled trials of interventions in tobacco users to reduce amount smoked, or to reduce harm from smoking by means other than cessation. Outcomes were change in cigarette consumption, markers of cigarette exposure and any markers of damage or benefit to health, measured at least six months from the start of the intervention.
We pooled trials with similar interventions and outcomes using a fixed-effect model. Other studies were summarised narratively.
Sixteen trials evaluated interventions to help those who smoke, to cut down the amount smoked and three compared different types of cigarettes or potentially reduced-exposure products. Self-reported reduction in cigarettes per day (CPD) was validated by reduction in carbon monoxide (CO) levels. Most trials tested nicotine replacement therapy (NRT) to assist reduction. In a pooled analysis of nine trials, NRT significantly increased the odds of reducing CPD by 50% or more for people using nicotine gum or inhaler or a choice of product compared to placebo (n = 3429, risk ratio [RR] 1.72; 95% confidence interval [CI] 1.41 to 2.10). Where average changes from baseline were compared for different measures, CO and cotinine consistently showed smaller reductions than CPD. Whilst the effect for NRT was significant, small numbers of people in either treatment or control group successfully sustained a reduction of 50% or more. Use of NRT also significantly increased the odds of quitting (RR 1.73; 95% CI 1.36 to 2.19). One trial of bupropion failed to detect an effect on reduction or cessation. Four trials of different types of advice and instructions on reducing CPD did not provide clear evidence. One study comparing cigarettes with different tar levels and one study of carbon filters showed some reduction in exposure to some toxicants but it is unclear that the risk of harm would alter substantially. A study of an electrically heated cigarette smoking system showed some evidence of improvement in markers of cardiovascular risk.