Financial incentives work to help people stop smoking and remain smoke free - according to research led by the University of East Anglia (UEA).
Evidence published today in the Cochrane Library provides strong evidence that financial incentives helped people to stop smoking, and stay stopped long term.
The review also found that incentives helped pregnant women stop smoking.
Lead author Dr Caitlin Notley, from UEA's Norwich Medical School, said: "Smoking is the leading cause of disease and death worldwide. Most smokers want to quit, but stopping smoking can be really challenging.
"Quitting smoking can greatly improve peoples' health. Rewards, such as money or vouchers, have been used to encourage smokers to quit, and to reward them if they stay stopped. Such schemes have been used in workplaces, in clinics and hospitals, and within community programmes.
"We wanted to know whether these schemes actually work long term, as previously it was thought that perhaps incentives only worked for the time that they were given. We found that they do help people stay smoke free, even after the incentive scheme ends.
"The cost of smoking to the economy is huge - around £13 billion to the UK economy, including over £3 billion for NHS and social care and £7.5 billion to lost productivity. So these types of schemes could help save money as well as lives."
The team investigated whether rewards such as cash payments, vouchers, or the return of money deposited by those taking part, worked. The review summarizes the results from 33 randomised controlled trials involving more than 21,600 people from eight countries. They included ten trials that focused on pregnant smokers who were rewarded with vouchers for quitting and staying smoke free.
All of the trials in the general population followed participants for at least six months and those who quit were checked by testing their breath or bodily fluids.
Some of the studies did not provide enough data for the team to fully assess their quality. But taking out the lowest quality trials from the analysis did not change the results.
The researchers say that the certainty of their findings in the general population is high. Their certainty about the findings in pregnant women is moderate, as there weren't as many studies and some were lower quality.
Dr Notley said: "We found that six months or more after the beginning of the trials, people receiving rewards were approximately 50 per cent more likely to have stopped smoking than those in the control groups.
"In people not receiving incentives, approximately seven per cent had successfully quit for six months or longer, compared to approximately 10.5 per cent of those receiving incentives.
"This is an important increase when we consider the enormous harms of smoking, and benefits of quitting, and suggests that incentives can be a useful part of a comprehensive approach to help people quit smoking. Another really important thing is that success rates continued beyond when the incentives had ended."
The total financial amount of incentives varied considerably between trials, from zero (self-deposits), to a range of between £35 ($45 USD) and £912 ($1185).
Dr Notley added: "For pregnant women, we also found that women in the rewards groups were more likely to stop smoking than those in control groups - both at the end of the pregnancy and after the birth of the baby, suggesting incentives may be a useful part of a comprehensive approach to helping pregnant women quit smoking.
"Stopping smoking during pregnancy is the best thing that women can do to improve their chances of having a healthy pregnancy. Staying stopped after the birth has great benefits for babies too, through avoiding exposure to second hand smoke."