Background:
The prevalence and correlates of hardcore smokers, who have high daily cigarette consumption, no quitting history and no intention to quit, have been studied in several western developed countries, but no previous trials of smoking cessation have tested intervention effectiveness for these smokers. The current study examined if hardcore smokers can benefit from smoking reduction intervention to achieve cessation, and explored the underlying reasons.

Methods:
A posteriori analysis was conducted on data from a randomized controlled trial of smoking reduction intervention on 1,154 smokers who did not want to quit. Odds ratios of 7-day point prevalence of abstinence, smoking reduction by at least 50% and quit attempt at the 6-month follow-up comparing subgroups of smokers were analyzed.

Results:
In hardcore smokers, the odds ratio comparing the quit rate between the intervention and control group was 4.18 (95% CI: 0.51-34.65), which was greater than non-hardcore smokers (OR = 1.58, 95% CI: 0.98-2.54). The number needed to treat for hardcore and non-hardcore smokers was 8.33 (95% CI: 5.56-16.67) and 16.67 (95% CI: 8.33-233.64), respectively. In smokers who did not have quit attempt experience and those who smoked more than 15 cigarettes daily, the odds ratio comparing intervention and control group was 3.29 (95% CI: 0.72-14.98) and 1.36 (95% CI: 0.78-2.36), respectively.

Conclusions:
The a posteriori analysis provided pilot results that smoking reduction intervention may be effective to help hardcore smokers to quit and reduce smoking. Having no previous quit attempt was identified as more important than having large cigarette consumption in explaining the greater effectiveness of the intervention.