TV ads and movies that portray the use of alcohol are an immediate stimulus for drinking among young people, according to a study published on Wednesday.
Dutch scientists recruited 80 male university students in an innovative experiment on pro-alcohol messages.
The guinea pigs watched a movie in a specially set-up lab aimed at replicating conditions in which people watch TV at home with friends.
The room had a wide-screen home cinema, a comfy leather couch, easy chair, and a small table with an ashtray and potato crisps and nuts.
It also had a refrigerator that was stocked with bottles of beer, wine, cola and orange soda, and the volunteers could drink whatever they wanted.
The students were randomly assigned to one of four groups, which watched a one-hour movie clip and advertisements that offered either low exposure, moderate exposure or intense exposure to alcohol messages.
The researchers chose two films, both raucous comedies, and two different sequences of ads for the experiment.
One film was "American Pie 2" in which characters drank alcohol 18 times and alcoholic drink was portrayed an additional 23 times.
The other was "40 Days and 40 Nights," in which alcohol was far less prominent. It was consumed only three times and alcoholic drinks were shown 15 times.
The ad sequences were either completely non-alcoholic -- featuring a car and a video camera, and so on -- or had two commercials for alcohol interspersed with neutral ones.
The students watched the movie in friendship pairs, and while they were doing this, they were discreetly filmed to monitor how often they reached for a bottle and how much they sipped.
Those who were exposed to high-intensity alcohol messages (they watched "American Pie 2" and the ads that included products for alcohol) each drank nearly three 200ml (6.8 fluid ounce) bottles of alcohol during the hour on average.
At the other end of the scale, those who watched the "non-alcohol" film and the neutral ads drank only one and a half bottles on average.
The most anyone drank during the experiment was four bottles, and the least amount drunk was none.
"This is the first experimental study to show a direct effect of exposure to alcohol portrayals on TV on viewers' immediate drinking behaviour," said lead researcher Rutger Engels, a professor in developmental psychopathology at the B ehavioural Science Institute at Radboud University Nijmegen.
"Our study clearly shows that alcohol portrayals in films and advertisements not only affects people?s attitudes and norms on drinking in society, but it might work as a cue that affects craving and subsequent drinking in people who are drinkers.
"This might imply that, for example, while watching an ad for a particular brand of beer, you are not only more prone to buy that brand next time you are in the supermarket, but also that you might go immediately to the fridge to take a beer."
The findings have important implications for policymakers struggling to address excessive drinking among specific groups, such as young men.
"It may be sensible to cut down on the portrayal of alcohol in programmes aimed at these groups and the commercials shown in between," the study suggests.