A study says teen smokers who try to quit only realize they're addicted when it's too late.

Researchers at the University of Montreal charted the course of nicotine addiction in teens for five years, establishing several common milestones.

They found that adolescents make their first serious attempt to nix the habit after only 2 1/2 months.

But the teens frequently keep puffing anyway.

The researchers found it's usually not until nearly two years passes that the teens' addiction dawns on them, and by that point their confidence to quit is shattered.

The study is published online in the American Journal of Public Health.

The study followed 319 students ages 12 or 13 who had never smoked but picked it up during the five years of the research.

Menthol levels manipulated

The Associated Press

; New York Times News Service

Tobacco companies deliberately changed the menthol levels in cigarettes depending upon who they were marketing them to.

Lower levels are for young smokers who preferred the milder brands and higher levels to lock in lifelong adult smokers, say researchers at the Harvard School of Public Health.

The researchers reviewed industry documents dating back decades on product development and on strategic plans for menthol products.

They said that the tobacco companies researched how controlling menthol levels could increase sales among specific groups.

Milder brands with lower menthol levels appealed to younger smokers. The milder products were then marketed to young consumers.

Identifying potential smokers

Want to know how likely it is that sixth graders will take up smoking? Ask them how easy it is to get a cigarette. If they say easy, a new study suggests they're more likely to become smokers by high school. And if they also say they have friends who smoke, they're even more likely to start.

Researchers, led by Dr. Chyke A. Doubeni, said knowing which children fit this description might make anti-smoking interventions more effective.

At the start of the study, in the Annals of Family Medicine, 168 students said they had smoked, 21 per cent said it would be easy to get cigarettes, and 9 per cent said they had friends who smoked.

By 10th grade, 177 more students had tried it, with 109 becoming regular smokers. About a third of those interviewed said they knew at least one store that sold cigarettes to youths.