The growth in the use of e-cigarettes has not led to a boom in teenagers taking up tobacco smoking, research suggests.
A new study found there was scant evidence that e-cigarettes had led to young people thinking regular smoking was cool.
The study, published in the journal Tobacco Control, examined data from 248,324 teenagers aged 13 to 15 from England, Wales and Scotland who took part in national surveys from 1998 to 2015.
Experts, led by a team at Cardiff University, said the studies happened at the same time as the "unregulated growth of e-cigarette use" between 2011 and 2015.
The results showed a drop in the proportion saying they had ever smoked regular cigarettes and a decline in those regularly smoking.
This was alongside fewer young people smoking cannabis or drinking alcohol, the study found.
The authors concluded: "These analyses provide little evidence that re-normalisation of youth smoking was occurring during a period of rapid growth and limited regulation of e-cigarettes from 2011 to 2015."
Overall, the percentage of young people who said trying a cigarette was "ok" fell from 70% in 1999 to 27% in 2015, with the rate dropping faster from 2011 onwards.
The percentage who had ever smoked fell from 60% to 19% between 1998 and 2015, while the proportion of regular smokers fell from 19% to 5%.
Read more: Increase in people quitting smoking in Wales