Men who try hypnosis to help them quit smoking are more likely to succeed than women who use the same treatment, research shows.
Women may find it harder to quit smoking generally
Studies of over 5,600 people found about 30% of men hypnotised stopped smoking compared with only 23% of women.
The Ohio State University scientists said this might be because women find it hard to quit smoking generally.
They spoke this week at the American Psychological Society meeting this.
None of the 18 studies that Dr Joseph Green and colleagues looked at examined why hypnosis might work better for men than women.
But Dr Green, assistant professor of psychology at the university, said the gender difference was important.
"When you have a 7% advantage for men, that's important, particularly when success rates after a year are often in the 20-30% range anyway.
"My suspicion is that the gender differences are not unique to hypnosis, but are connected to difficulties women have in trying to quit smoking in general," he said.
He said women were equally susceptible to hypnosis as men, if not more.
"Given that most smoking cessation approaches have similar success rates, it is really up to the consumer," he said, and recommended people find the best treatment to suit them.
Harder for women
Dr Peter Whorwell from Wythenshawe Hospital in Manchester, who treats irritable bowel syndrome patients with hypnotherapy, said: "I think there are lots of gender differences going on.
"We have a gender difference with irritable bowel the other way round - men do not do quite so well as women.
"It's terribly complicated. Gender is different to sex. You have a sex basis which is purely hormones, and that can be important.
"Then you have got the gender, the emotional component of sex, and how that might affect people's ability to get better or, in this case, quit smoking.
"I would agree that it's probably nothing to do with hypnotisability," he said.
But he said it may be that people seeking hypnotherapy to stop smoking were doomed to fail because they did not truly want to quit.
"You have got to want to quit smoking. Hypnotherapy is very much in the power of the individual to make it work," he said.
A spokeswoman from Action on Smoking and Health (ASH) said: "There have been some studies showing that women find it harder to quit. But the government figures on smoking cessation do not show much of a difference between men and women.
"Hypnosis is not a recognised, approved method of quitting, but there is anecdotal evidence that it helps some people," she said.