The study was carried out by researchers at St George's, University of London and the University of Hertfordshire.

Co-author Dr James Erskine, a psychologist at St George's, says the study shows that many smokers attempting to give up -- as well as people trying to quit other vices -- may be thwarted by the very technique they use to stop.

Dr Erskine said: "These findings have obvious implications for individuals seeking to give up certain behaviours, for example, smoking, overeating, drinking, sex and other excessive behaviours.

"If trying to avoid thoughts of something in an attempt to give it up actually unwittingly triggers a subsequent increase, it's a poor method of achieving self control. This work may stop people using quitting techniques that are ultimately harmful."

Dr Erskine and his team set out to test whether smokers experienced behavioural rebound -- the phenomenon where trying not to think about something leads to an increase in the behaviour. Their previous research into eating behaviour and thought suppression showed that people trying not to think about chocolate subsequently ate much more than people who were deliberately thinking about it. However, previous studies only examined behavioural rebound over a period of five minutes, rather than days and weeks.

Eighty five smokers, who smoked at least ten cigarettes a day, took part in the latest study, which has been published in the journal Psychological Science. They were split into three groups and asked to monitor their cigarette intake over three weeks. All three groups were asked to behave as usual in the first and third weeks. But in the second week one group of 30 people was told to suppress their thoughts of smoking, and one group of 29 people was told to actively express thoughts about smoking. A control group of 26 was told not to change anything.

The first week's results showed that each group smoked a different average number of cigarettes, so the researchers applied a formula to the following weeks' results to ensure they were comparing like for like.

The results showed that neither the expression group nor the control group differed significantly in the number of cigarettes smoked from week to week. However, in the second week the suppression group smoked, on average, nearly five less cigarettes each than the expression group and almost four less than the control group. And in the third week -- when they stopped suppressing their thoughts -- the suppression group smoked nearly three more than the expression group and the control group. From the raw results, the suppressions group's increase from week two to three was six cigarettes per person, roughly three more each than smoked in the first week.

Dr Erskine said: "This shows a clear behavioural rebound. The fact that the suppression group smoked less in the second week shows that this method may be effective in reducing unwanted behaviour in the short term. But this actually isn't helpful, as smokers might then think that thought suppression is a useful strategy in quitting smoking.

"In this case, we asked the suppression group to stop suppressing in week three, but the rebound effect should be the same whether it is deliberate, or whether other real life factors cause someone to stop suppressing thoughts of smoking. In real life, it can be hard to continue suppressing your thoughts.

"Although the differences in the number of cigarettes smoked from week to week may seem small, we know that habitual smokers are remarkably consistent in how many they smoke. So, even a small difference can be considered significant.

"Knowing what techniques not to use should lead to better understanding of what methods of quitting do work."

Note: If no author is given, the source is cited instead.

• Smoking
• Lung Cancer
• Staying Healthy

• Smoking Addiction
• Behavior
• Addiction

• Bronchitis
• Tobacco smoking
• Self-harm
• Lung cancer
• Social cognition
• Cognitive dissonance