Warning labels on cigarette packs help former smokers to avoid lighting up again, Canadian and international researchers say.

Canada's graphic warning labels have covered half of each pack's surface on both sides since 2000, when it became the first country to introduce them.

The health risks described on the packages deter non-smokers from starting and stop teens who dabble with cigarettes from becoming confirmed smokers. But there wasn't clear evidence on whether they help ex-smokers to continue to butt out.

The answer is yes, according to 1,936 people who'd quit in the previous year and were participating in the International Tobacco Control 4-Country survey. The research project monitors the impact of smoking policies in Canada, Australia, the UK and the U.S.

"This study provides the first longitudinal evidence that health warnings can help ex-smokers stay quit," David Hammond of the department of health studies and gerontology at the University of Waterloo and his co-authors concluded in this week's issue of the journal Tobacco Control.

In total, 57.5 per cent of the participants who had quit said they were still not smoking after a year.

Resisting smoking temptation

In telephone interviews, respondents were asked how often in the previous month they had noticed a warning label — never, rarely, sometimes, often, or very often.

They were also asked to what extent the warnings caused them to reflect on the risks of smoking to their health, ranging from not at all, a little, somewhat, or a lot.

Successful quitters who reported that warning labels caused them to be "a lot" more likely to stay quit showed a relapse rate of 41 per cent compared with 50 per cent among those who said they didn't find the warnings helpful.

New, more explicit graphics for cigarette package labels are starting to circulate. (Canadian Press)

"We theorize that the mechanism by which [they] help ex-smokers to stay quit involves some sort of active use of the warnings — for example, to help generate reasons for resisting temptations to relapse, and is not something that occurs automatically," the study's authors wrote.

"We recommend that health professionals encourage all quitters to consider pack warnings as a potential tool to help counter their urges to resume smoking."

Size of warnings

The investigators speculated that those who said warning labels really helped them to stay quit either consciously or subconsciously come up with strategies to use them.

Both the size and novelty of the graphics labels were associated with remaining abstinent.

Country of residence did not make a major difference in predicting relapse, even though the size and type of warning labels differ between countries.

In the U.S., the warning labels are text only and are placed on the side of the pack compared with larger more graphic displays in the other countries studied.

The average age of the participants was 46 and slightly more than half were women.

The researchers considered factors such as how many smokers the participants said they had among their friends, relapse predictors like frequency of urge to smoke and the number of cigarettes smoked per day in the analysis.

Earlier this week, Imperial Tobacco Canada announced it was launching a constitutional challenge of the federal government's decision to increase the size of graphic health warnings on cigarette packages to 75 per cent. JTI-Macdonald Corp. also launched a similar legal challenge.

Last week, anti-smoking groups said the federal government's tobacco control strategy has been highly successful but cuts to its budget will put the health of Canadians at risk and mean increased health care costs.

The study was funded by the Roswell Park Cancer Institute, the U.S. National Cancer Institute, the Robert Wood Johnson Foundation, the Canadian Institutes of Health Research, the National Health and Medical Research Council of Australia, Cancer Research UK, the Canadian Tobacco Control Research Initiative, the Center for Behavioral Research and Program Evaluation and the National Cancer Institute of Canada.