Picture warnings on cigarette packets depicting the dangers of smoking make little impact on teenage smokers, a study suggests.
The UK introduced the images, which depict things such as diseased lungs and heart surgery, in 2008.
But the Stirling University study, which involved 2,800 children, found the images have had almost no effect on deterring 11 to 16-year-old smokers.
However, they did have an effect on non-smokers and experimental smokers.
The study - published by the Tobacco Control journal - looked at data from the Youth Tobacco Policy Survey before and after the introduction of the images. Before the introduction of the images only text warnings were used.
Of the 2,800 children who were questioned, one in 10 was a smoker, while the others were either non-smokers or children who had just experimented with smoking.
'Tackle illicit trade'
While the proportion of youngsters who thought the warnings were capable of putting them off increased after the introduction of the images among both non-smokers and experimenters, the number of smokers who were put off remained almost constant - it went up from 13% to only 14%.
Lead researcher Dr Crawford Moodie said that while it was disappointing that the images did not seem to have an impact on smokers, the rise in the numbers of non-smokers and experimenters being deterred was a "really positive" result.
But he said there was also a risk of people becoming desensitised - the images and text warnings have not changed since they were introduced in 2003 and 2008 respectively.
"Other countries regularly change their warnings. I think if we rotated them here they would have more impact."
Simon Clark, who is the director of the smokers' group Forest, said: "Everyone, including teenagers, knows there are health risks associated with smoking".
"Increasing the size of the warnings, or putting them on the front of the pack, will make no difference.
"If you want to smoke you will smoke, regardless of the size or position of the warning.
"If governments want to reduce youth smoking rates they should crack down on shopkeepers who sell cigarettes to children and tackle illicit trade.
"They could also ban proxy purchasing and make it illegal to buy cigarettes if you are under 18."