Young people who use e-cigarettes could be more likely to later smoke tobacco, according to a new Scottish study.
A link was found between the use of the devices by those who had never tried smoking and their first experimentation with cigarettes in the following year.
People in Scotland aged between 11 and 18 were surveyed in February and March 2015 and then again a year later.
The research found 40% of those trying an e-cigarette in the first survey went on to smoke tobacco.
The study was carried out by the DISPLAY Team, a collaboration between the universities of Stirling, St Andrews and Edinburgh, as well as social research institute ScotCen.
Dr Catherine Best, research fellow at Stirling University, said: "Our findings are broadly similar to those from eight other US studies.
"However, this is the first study to report from the UK.
"Uniquely, we also found that e-cigarette use had a greater impact on the odds of cigarette experimentation in young 'never smokers' who had a firm intention not to smoke and/or whose friends didn't smoke.
"Traditionally, this is the group of young people least likely to take up smoking."
The initial 2015 survey found that 183 of the 2,125 who had never smoked said they had tried an e-cigarette and 1,942 had not.
Pupils at four Scottish secondary schools took part in the study.
Only 249 (12.8%) of young people who had not tried an e-cigarette went on to try tobacco.
Sally Haw, professor of public and population health at Stirling University, said: "The greater impact of e-cigarette use on young people thought to be at lower risk of starting smoking is of particular concern.
"Further research is required to discover how experimentation with e-cigarettes might influence attitudes to smoking in young people traditionally at lower risk of becoming smokers; and importantly how many of this group who do experiment with cigarettes go on to smoke regularly."