Background:
This presentation explores over-time changes in smokers' reactions to pictorial health warning labels (PWLs) and impact on subsequent quitting in Thailand where PWLs on tobacco packs were first implemented in 2005 and were revised in 2007, 2010, 2011, and 2014.

Methods:
Nationally representative longitudinal data from six waves of the ITC Thailand Survey (2005-2012) were analyzed, involving a cohort of 2,000 smokers aged 18 years and older at baseline. The primary outcome was subsequent quitting behavior, including intentions to quit, quit attempts, and successful quitting.

Results:
Descriptive analyses show that the effectiveness of the PWLs increased over time, evidence of the positive benefits of periodic increases in PWL size and changes in content to minimize the over-time reductions in PWL effectiveness shown in other ITC countries (e.g., Canada, US, Mauritius, Australia) when warnings have not changed. Specifically, there were increases in the percentage of smokers who often/very often noticed the warning labels, read the warning labels closely, reported that the PWLs made them think of harm of smoking, reported that PWLs influenced them to think about quitting a lot, and reported that PWLs stopped them from smoking more than once. Preliminary bivariate analyses found that there was a significant association between these indicators of warning effectiveness and subsequent attempts to quit. Additional analyses will examine whether these indicators also predict subsequent intentions to quit, quit attempt, and successful quitting when controlling for other known predictors of quitting.

Conclusions:
The new PWLs on tobacco products implemented in 2005 with periodic rotation appear to show increased effectiveness over time among adult smokers in Thailand. More research is needed to understand the extent to which the health warnings contribute to the public health objective of increasing cessation among smokers and decreasing uptake among non-smoking youth.