Background and Aims Past research has found that young smokers are more likely to make quit attempts; however, there are conflicting findings regarding age and quit success. This study examined the degree to which smoker age is related to making quit attempts and quit success. Design Ten waves of the International Tobacco Control Policy Cohort survey (ITC-4C) collected between 2002 and 2014, with nine wave-to-wave transitions with predictors at the first wave predicting quit attempts and success by the next wave. Setting Canada, the United States, the United Kingdom and Australia. Participants Data from 15 874 smokers categorized into four age groups at baseline (18-24, 25-39, 40-54 and 55+ years). Measurements Age, quit attempts and success (defined as ≥ 30 days abstinence confirmed, if possible, on a third wave for recent attempts). Findings Older smokers were more likely to smoke daily (χ 2 = 1557.86, r = 0.136, P < 0.001) than younger smokers. Daily smokers were less likely to report quit attempts (38.1 versus 58.2%) and to achieve 30 days of abstinence (22.9 versus 34.3%) than non-daily smokers. Older daily smokers were less likely to make quit attempts [0.61, confidence interval (CI) = 0.54-0.70, P < 0.001], even after controlling for indicators of nicotine dependence, country, sex, education, income, relationship status and household composition, than younger smokers. Younger smokers (< 25) were more likely to succeed for at least 30 days of abstinence, but only when compared with those aged 40-54 (OR = 0.83, 95% CI = 0.68-0.99). However, when controlling for heaviness of smoking the age effect disappeared. Significant interactions with age were found between age and intention when predicting quit attempts, and age and heaviness of smoking when predicting quit success. ConclusionsAn international cohort study indicates that young smokers are more likely to attempt to quit and appear to have similar levels of success in abstaining from smoking compared with older smokers when controlling for dependence. Quit success in all ages is most predicted by lower levels of nicotine dependence.

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Background Tobacco smoking is a highly prevalent, addictive behaviour and a key public health priority. However available cessation therapies have low quit and high relapse rates, indicating an urgent need for more effective treatments. Predicated on promising preclinical and pilot clinical data, this paper presents a rationale and protocol for the trial of N-acetylcysteine (NAC) as a novel anti-craving smoking cessation aid. Methods Current smokers (n = 120) of at least 10 cigarettes a day are recruited through online advertisements, print publications and dissemination of flyers. Participants are randomised on a 1:1 ratio to receive either 16-week treatment of 1.8 g/day of NAC or placebo with all participants receiving quit support from the online QuitCoach tool. Participants are attending visits at baseline, 8 and 16 weeks with a 42-week post-discontinuation follow-up. The primary outcome measure is sustained abstinence at six months after treatment based on self-reported rating scales and confirmed by exhaled carbon monoxide and salivary cotinine levels. Secondary outcomes are timing of the first lapse and relapse, between-group cigarette consumption, withdrawal symptoms, general wellbeing and mood/anxiety symptoms. Between-group differences in adverse events and subgroup analyses for variables including gender and Diagnostic Statistics Manual 5 diagnostics will also be investigated. Discussion The planned trial addresses an issue of major importance to human health and, if an effect is shown, may result in substantial changes to the management of smoking and nicotine addiction with overt public health implications. Trial registration Australian New Zealand Clinical Trials registry (ANZCTR), ACTRN12617001478303. Registered on 19 October 2017.

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