A woman's genes may scupper any attempts to give up smoking using a nicotine patch, a study suggests.
Patches may be more effective for men
Researchers at Oxford University found nicotine patch therapy had no effect in women with a particular gene type.
However genetic makeup appeared to have no effect in men's success in quitting with nicotine patches.
The findings, published in the British Medical Journal, suggest social factors may play a bigger role in determining women's smoking behaviour.
Dr Patricia Yudkin and colleagues looked at 752 people who had taken part in a nicotine patch trial at various intervals over eight years. All had been heavy smokers.
They determined abstinence in people by measuring the level of cotinine, a by-product of nicotine, in the blood.
They also examined a gene controlling the working of a receptor in the brain stimulated by the chemical dopamine.
It is thought that when these receptors are stimulated they trigger feelings of pleasure.
Nicotine causes the release of dopamine and stimulates the receptors.
The gene comes in two variants, known as the T and CC alleles.
The researchers found a high response to nicotine patches among women with the gene variant T allele, but almost no response in women with genotype CC.
Figures were stable among men in both genotype groups.
In the study 60% of both men and women had the CC type of gene.
The authors suggest nicotine replacement therapy could be more effective if targeted at those most likely to respond.
However Dr Yudkin said the reason why women react differently to men is not known.
"It could be because non-nicotine factors play a more important role in women's smoking behaviour than men's," she told BBC News Online.
"Other researchers have found that social and behavioural aspects of smoking, such as having something to hold or put in the mouth, are more important to women than men."
She said further studies need to be done, but it is possible that in the future, women could be tested easily and cheaply for genotype.
"We could also advise those with the CC genotype not to use nicotine replacement. Other forms of therapy are likely to work better for them."
Dr John Moore-Gillon, president of the British Lung Foundation said the research was interesting.
"We would encourage anyone who wants to stop smoking to explore all methods available including smoking cessation clinics.
"In particular women should, in light of this research, persevere and keep trying to quit for sake of their health," he told BBC News Online.
Dr Colin O'Gara, of the charity Action on Addiction, said: "This research has important implications for the treatment of nicotine addiction and in understanding the molecular basis of nicotine dependence.
"Only 20% of people succeed in giving up in the long term even with the best treatment currently available. If we can identify which treatments are most suitable for people by doing a simple test this could save unnecessary costs and side-effects."