Smokers who used e-cigarettes consumed fewer of the traditional version than those who did not.

Vaping could initially help people quit smoking cigarettes, but relapse is common among those who substitute e-cigarettes for tobacco products.

E-cigarette use is rising, particularly among smokers looking to quit their combustible-cigarette habit. But it is still unclear how much e-cigarettes actually aid smoking cessation.

Ramchandar Gomajee at the Sorbonne University in Paris and his colleagues analysed data from 5,400 smokers and 2,025 former smokers. The researchers found that the average number of combustible cigarettes smoked per day by people who regularly used e-cigarettes fell by 4.4 over roughly 2 years, compared with only 2.7 for those who did not use e-cigarettes. Sixty-seven per cent more e-cigarette users than non-users quit smoking altogether.

But there were 70% more relapses among former smokers who used e-cigarettes than among those who did not use the devices.