An Update on Hardening: A Qualitative Review

Area of Science:

• Public Health
• Smoking Cessation Research
• Behavioral Science

Background:

• The hardening hypothesis posits that the remaining smokers are less likely to quit, leading to decreased quit rates over time.
• This hypothesis suggests a need for more intensive treatments or harm reduction strategies for persistent smokers.

Purpose of the Study:

• To review population-based evidence examining the hardening hypothesis in smoking cessation.
• To determine if the prevalence of becoming a former smoker is decreasing due to fewer quit attempts or reduced success rates.

Main Methods:

• A comprehensive search of major databases (PubMed, EMBASE, PsychINFO) and trial registries was conducted.
• Population-based surveys reporting changes in smoking cessation outcomes over time were included.

Main Results:

• None of the 26 reviewed studies found a decrease in conversion from current to former smoking over time.
• Several studies indicated an increase in quit attempts and success rates, contradicting the hardening hypothesis.
• These findings remained consistent across various study characteristics, including dates, duration, data sources, and nationality.

Conclusions:

• The hardening hypothesis is not supported in the general smoking population.
• Smoking decline is slower in specific subgroups (older, women, low socioeconomic status, those with comorbidities), likely due to less quitting in these groups.
• The anomaly of stable or increasing quit success despite increasing prevalence of risk factors warrants further investigation.