Objective Determine if an automated email messaging system that sent Individually Timed Educational Messages (ITEMs) increased the effectiveness of an Internet smoking cessation intervention.

Design Using two consecutive series of participants, we compared two web-based self-help style smoking cessation interventions: a single point in time educational intervention and an enhanced intervention that also sent ITEMs timed to participants' quit efforts. Outcomes were compared in two series of consecutive participants: 199 receiving the one-time intervention and 286 receiving ITEMs.

Measurements Demographic factors, number of cigarettes smoked, nicotine addiction, depressive symptoms and confidence in ability to quit were measured at entry. 24-hour quit attempts and 7-day point-prevalence of abstinence (non-respondents assumed to smoke) were measured 30 days after each subject's self-selected quit date.

Results The one-time and ITEMs groups differed in some demographics and some relapse risk factors, but not in factors associated with 30-day quit rates. ITEMs appeared to increase the rate at which individuals set quit dates (97% vs. 91%, p=0.005) and, among respondents to follow up questionnaires (n=145), the rate of reported 24 hour quit efforts (83% vs. 54%, p=0.001). The thirty-day intent-to -treat quit rates were higher in the ITEMs group: 7.5% vs.13.6%, p=0.035. In multivariate analyses controlling for differences between groups, receiving ITEMs was associated an increase in the odds ratio for quitting of 2.6 (95% confidence interval 1.3 to 5.3).

Conclusion ITEMs sent on strategic days in smokers' quit efforts enhanced early success with smoking cessation relative to a single point in time web intervention. The effect appears to be mediated by ITEMs causing smokers to plan and undertake quit efforts more frequently.