The dangers of smoking are not news: Cigarette packs have carried those little black box warnings for decades. But just what is the best way to phrase messages about the evils of lighting up so that smokers are motivated to quit?

The answer appears to depend on how confident smokers are that they will be able to quit, according to researchers at Georgetown University.

Most warnings on cigarette packs in the U.S. and worldwide focus on the negative health effects of cigarettes. However, these messages may not encourage a certain population of smokers to quit. As Darren Mays, lead author of the study told TheDoctor, some people respond better to positive messages that emphasize the benefits of quitting.

Trying to figure out which smokers need gentle persuasion and which need the shock of scare tactics in order to quit.

It may take both positive and negative messages to convince America’s estimated 45 million smokers to put down their cigarettes, Mays, an assistant professor of oncology at Georgetown University Medical Center and the Lombardi Comprehensive Cancer Center, said. “Our study shows that framing messages to address smokers’ pre-existing attitudes and beliefs may help motivate them to quit.”

So which smokers need to be gently encouraged and which benefit more from the shock of a scary message?

The 740 young smokers in the study (aged 18 to 30) were asked at the start if they thought smoking was harmful to their health; if they felt they could quit smoking within the next three months; and how easy they thought it would be to quit smoking within the next three months.

Researchers then had participants view online images of cigarette packs with pictures depicting one of four health risks associated with smoking: lung disease, cancer, heart disease, and death.

One picture portrayed a man using a breathing apparatus. Another was of two sets of lungs, one healthy and one diseased. Another showed a man lying in bed with stitches on his chest, and a fourth a cancerous mouth.

The message accompanying the photos on each pack was either a negative one (such as “Cigarettes can kill you”) or a positive one (such as “Quitting smoking reduces the risk of death due to tobacco”).

Smokers who had less confidence in their ability to quit were more motivated by positive messages about the benefits of quitting. The young smokers who felt more confident responded better to negative messages about the perils of continuing to light up.

It is possible that nicotine patches and medication could also be used to help boost smokers' confidence in their ability to quit.

The next step will be to test the effect of positive or negative messages in the real world. Basically, Mays says, this would mean putting different types of messages on smokers' cigarette packs and then watching to see whether a certain message helps them reduce their smoking or quit totally.

The study is published online in Nicotine & Tobacco Research.