Introduction:
Aim and objective: Motivations that lead adolescents to consume substances are diverse and include the interaction of genetic and environmental factors. Project EX program has shown substantial evidence of efficacy for quitting smoking among adolescents, and is the only empirically-validated school-based smoking-cessation intervention for adolescents in Spain. Motivation, self-efficacy, and nicotine dependence have proven to be mediators of the efficacy of Project EX to reduce and quit smoking. However, more evidence is needed on what mechanisms are underlying this intervention’s effects in the long-term. This longitudinal study aimed to test smoking intention as a mediator of Project EX’s intervention efficacy to reduce tobacco use in Spanish adolescents.

Methods:
Six high Spanish schools were randomly selected to participate in the program condition or the waiting-list control group with baseline, immediate-posttest, and 12-month follow-up assessments. At baseline, 685 adolescents aged 14-20 years (mean age: 14.87; SD = .92; 47.4% were females) were evaluated using self-administered tests of tobacco, and smoking intention. A biomarker of smoke inhalation, a measurement of exhaled carbon monoxide (ECM), was used. Mediation analyses were conducted using the PROCESS v2.12 macro for Windows.

Results:
Project EX had a significant effect on smoking intention. Indirect effects indicated that Project EX reduced the ECM level, and number of cigarettes used.

Conclusions:
Interventions that reduce consumption intention at short-term are more likely to be successful in decreasing tobacco consumption in the long-term.

Funding:
This research was supported by the Spanish Department of Economy and Competitiveness (PSI2011-26819).