Researchers from the Tobacco Use Research Center at the University of Pennsylvania may have found at least part of the answer - genetics.

Two genes pinpointed
Two genes in particular seem to help smokers quit successfully, and this same combination of genes also makes them less likely to start smoking again, report the researchers in the October issue of Health Psychology.

This study provides the first evidence that genes that alter dopamine function may influence smoking cessation and relapse during treatment, study author Caryn Lerman, associate director for Cancer Control and Population Science at the University of Pennsylvania, says in a press release.

Dopamine is a neurotransmitter that acts as a messenger between nerve cells in the brain.

The research study
Lerman and her colleagues studied 418 people who were enrolled in a clinical trial to test the effectiveness of the antidepressant bupropion for smoking cessation. The study participants either received a placebo or bupropion for 10 weeks and behavioural counselling.

Blood samples were taken from all of the participants for genetic analysis. Smoking status was assessed at the end of the 10 weeks and then again after six months.

People who had particular variants of a dopamine transporter gene (SLC6A3) and a dopamine receptor gene (DRD2) were more successful at staying off cigarettes and avoiding relapse than people who didn't have those variants.

Why is it hard for some?
One of the great mysteries in smoking cessation is why some people find it so easy and why it's so hard for others, says Robert Baker, director of the Ochsner Center for the Elimination of Smoking in New Orleans. I hear about people who have smoked for 40 years and then just put them down one day. Others haven't smoked as long and seem to have a much harder time. I think genetic factors do play a role.

Dr Marc Siegel, an internist at New York University Medical Center, agrees. It's not surprising to hear that someone's genetic makeup influences their response to quitting smoking. Some patients respond to Zyban (a form of bupropion), some to the patch (nicotine replacement therapy). Often, people who want to quit are encouraged by doctors to use Zyban and a patch - also in South Africa.

Targeted treatment in the pipeline
What's exciting about this research, Siegel says, is the possibility that one day doctors could specifically target smoking cessation treatment to each patient based on their genetic makeup. But such a therapy is likely a long time away. If you're waiting for a cure before you quit smoking, advises Baker, you may not live that long.

Despite some compelling reasons to quit - including an increased risk of many cancers, heart disease and a one in five chance of developing emphysema or chronic bronchitis, according to the American Cancer Society - many people still smoke.

The good news
The good news is that plenty of people - with and without these genes - have quit smoking.

You may have a more difficult time if you don't have these genes, says Baker, but you can still get off cigarettes. I'm sure there are thousands upon thousands who have done just that. - (HealthDayNews)

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