One fourth reported experiencing a sense of social denormalization of smoking, such as hiding their pack from view, using a case to cover their pack or feeling embarrassed about smoking.
"This is one of the first studies to show that the Australia plain packs have had an impact on smoking-related thoughts, feeling and behaviors among Australian adolescents and young adults," lead author Sally Dunlop of the Cancer Institute in New South Wales told Reuters Health.
Four years ago, Australia implemented the world's first legislation that required all cigarette packs to be plain as of December 2012. The plain packs are dark olive green cardboard with the brand name and number of cigarettes in a standard font and design on the front. Health warnings were updated and increased in size, now covering 75 percent of the front and 90 percent of the back of the packs.
"With comprehensive bans on tobacco advertising in Australia, the cigarette pack had become one of the last places that tobacco companies had to display their branding," Dunlop said by email. "By introducing plain packaging, the opportunity for tobacco companies to associate their deadly products with attractive imagery was greatly reduced."
Nearly 9,000 Australians participated in four phone surveys - in June of 2010, 2011, 2012 and 2013 - about their smoking habits, friends' smoking habits and opinions on the plain packaging. Before the plain packaging was introduced, participants were asked whether it was likely to change their habits or social status with regard to smoking, and after the law was in effect, they were asked whether it had.
Researchers found that reactions exceeded the participants' own expectations. After plain packs were implemented, 16 percent of never-smokers said they were less likely to try smoking as a result, whereas only 8 percent anticipated this effect in 2011. Similarly, 18 percent of experimenters and ex-smokers said the packs made them less likely to smoke again, while only 11 percent had anticipated that effect.
After the packs were introduced, 34 percent of current smokers reported the packaging had prompted them to try to quit or to think about quitting, but in 2011 only 14 percent thought they would feel that way.
Overall, support for the plain packaging rose, even among smokers, after it was introduced, compared to beforehand.
The study is the first to record an impact on social denormalization among young smokers, the authors write in Tobacco Control. Eight months after the introduction of the new packs, one in four young smokers felt embarrassed or hid their packs.
"It creates a social environment where smoking is no longer the norm," said Vicki White of the Centre for Behavioral Research in Cancer in Melbourne, who wasn't involved in the study.
"With tobacco companies continuing to argue ineffectiveness of plain packaging, it is of paramount importance that the effectiveness of plain packaging is discussed in the public domain," said Nichole Hughes, of the Nossal Institute for Global Health in Melbourne, who also was not involved in the study.
"The discussion about plain packaging will hopefully lead to greater community understanding about harmful tobacco use, as well as opportunities for ongoing research," Hughes told Reuters Health by email.
"Australia has comprehensive tobacco control policies, which work together, and the impact of one policy alone is difficult to demonstrate," she said. "However, the great momentum from Australia's legislation is continuing as the UK, France, Canada and New Zealand are all committing to plain packaging."
Australia's precedent also extends to legal precedents, which have upheld the regulations against industry challenges.
"Despite industry suggestions to the contrary, young people are highly supportive of plain packaging laws, including smokers themselves," said David Hammond at the University of Waterloo in Ontario, Canada, who wasn't involved with the study.
"Plain packaging in Australia is achieving many of the government's objectives and supports broader implementation of plain packaging in other countries," he said by email.