Does the Magnitude of Reduction in Cigarettes Per Day Predict Smoking Cessation? A Qualitative Review

Reduction in cigarettes per day (CPD) aided by nicotine replacement therapy (NRT) increases cessation in smokers; however, it is unclear whether this is due to use of NRT or reduction per se. If the latter, a greater magnitude of reduction in CPD should increase the odds of cessation.

The authors searched PubMed, Cochrane, PsychINFO, http://clinicaltrials.gov and their personal libraries for studies on smoking reduction. Seven of the 76 (9%) identified intervention trials and four of 28 naturalistic studies (14%) reported on the magnitude of reduction in relation to the odds of cessation.

Five of the seven intervention trials and three of the four naturalistic observational (cohort) studies found that increased reduction in CPD was associated with increased cessation. The intervention trials that reported effect sizes found that every 1% decrease in CPD or carbon monoxide was associated with a 3% to 4% increase in the odds of cessation. The naturalistic studies found that ordinal (eg, quartile) increases in participants' magnitude of reduction in CPD were associated with 50% to 290% increases in the odds of cessation. All of the naturalistic studies and four of the intervention trials included covariates; however, reduction's association with cessation could still be due to its association with NRT use or motivation.

Although prospective prediction does not necessarily indicate causality, our findings suggest reduction in CPD is a mechanism of increased cessation in prior NRT-aided reduction studies.