A range of research has given indications that a second addictive substance may be present. Now scientists at Victoria University and the Institute of Environmental Science and Research (ESR) have provided the most direct behavioural evidence yet that the hypothesis is true.
Dr Penny Truman, of ESR, will present results from their experiments in a talk, "More than just the devil you know", at the Smokefree Oceania conference in Auckland this week.
"This extra chemical is an additional thing that makes smoking harder to give up," Dr Truman told the Herald.
"It's going to have some effect on addiction. I believe if we are going to get the best smoking cessation methods we need to understand it."
The experiments with rats involved measuring the effort they were prepared to make to obtain intravenous doses of saline-based solutions of nicotine, tobacco smoke from factory-made cigarettes, or smoke from roll-your-own tobacco.
The rats had to press a lever an increasing number of times to obtain a single dose. They went to a greater number of lever-pushes for the roll-your-own doses than for the nicotine or the factory-mades.
The difference between nicotine and rollies was statistically significant, whereas that between nicotine and factory-mades was not. On one hand, this indicates the presence of an additional addictive component in the rollies; on the other hand, it shows not all types of tobacco/cigarettes have the same properties.
"The main conclusions from this study," the researchers write, "were that non-nicotinic components have a role in tobacco dependence, and that some tobacco products could have higher abuse liability, irrespective of nicotine levels."
Dr Truman said the research had produced strong results using the gold standard method for testing addictiveness.
"That is a formal proof that some tobacco substances are more addictive than nicotine is."
She said it was not yet clear what substance was behind the greater addictiveness of the dissolved rollie smoke over the nicotine solution.
"That's the million-dollar question ... We are following up a lead."
The director of Auckland University's National Institute of Health Innovation, Associate Professor Chris Bullen, said there had been questions about whether undisclosed chemicals were being used to enhance the addictiveness of smoking, and whether even nicotine-free cigarettes might still be addictive.
He said the new study was "a great piece of research".
"It could in part explain why nicotine replacement therapy and any other kinds of products that deliver nicotine as a substitute to mitigate withdrawal and cravings might not be as effective as they could be.
"It could lead to the development of enhanced-effectiveness medications to help smokers quit. That's the end goal of this kind of research - to identify what that missing piece could be, and address that with some kind of medication."
Plain-package law undermined by seductive names
Tobacco researchers have identified weaknesses in Australia's plain packaging law that they want eliminated when New Zealand writes its rules.
The Government is committed to plain packaging but has not yet revealed the legislation, which Associate Health Minister Tariana Turia has said she expects to be introduced to Parlianment this year.
Australia's rules last year imposed a standard dull brown colour and large pictorial health warnings but permitted brand names, such as Dunhill and Rothmans, and variant names.
Otago University marketing expert Professor Janet Hoek said this kind of sub-branding using evocative names like "infinite" could undermine the impact of plain packaging - the policy's aim was to reduce the appeal of tobacco and enhance perceptions of the harm it caused.
Allowing variant names was a loophole in the Australian law that should be rectified in New Zealand's version of plain packaging.
Her research group tested cigarette pack images of a theoretically attractive concocted brand, "Premium rich midnight red", in an online survey of young adult smokers. Reactions were compared with those for another made-up brand called "Red" cigarettes.
They detected no overall differences among survey participants' perceptions of how harmful each product might be, nor variations in expected ease of quitting.
But men saw Premium rich midnight red as significantly less harmful than women did.
"They [regulators] should be very cautious in what kind of descriptors they allow to be used on packaging," Professor Hoek said.
In separate research, she and her colleagues found that young people's support for tobacco to be forced into plain packaging has increased sharply.
Between 2009 and last year, support increased from 47 per cent to 64 per cent in the annual survey of Year 10 students by ASH (Action on Smoking and Health).
"The strongest determinant of support was smoking status," said Professor Hoek. "Non-smokers showed consistently higher support for plain packaging, a relationship that intensified over time. Students whose parents, siblings or friends smoked showed less support for plain packaging."
Her colleague, Dr Richard Jaine, will present research from the same data set, showing that support for a smokefree society increased over the four-year period.
Of the survey participants last year, 71 per cent expressed support for measures that would reduce the availability of tobacco products. Most also supported the idea of tobacco not being sold.
Youngsters 'slip into' tobacco habit
The idea that young adults make a free and independent choice to take up smoking has been challenged by findings from research among young people who had been smoking for less than eight years.
Otago University researcher Rebecca Gray and her colleagues interviewed the participants - aged 18 to 25 and who had started smoking since turning 18 - to investigate a tobacco industry claim that smoking is a matter of adult informed choice.
She found the research participants had made spur-of-the-moment decisions about smoking.
Instead of thinking carefully and making a conscious decision to become a smoker, there was evidence of participants "slipping" into a regular smoking habit.
There was a lack of understanding of the health risks, and people were over-confident about their ability to avoid addiction.
"Participants commented on the difficulty of communicating information about risk and addiction to young people who see themselves as unlikely to become addicted or face long term health risks," Ms Gray said.
She said some study participants had suggested that to help deter young people from taking up smoking, messages on addiction - including simulating the experience of addiction - could be delivered by people in the same age range.
