In the film Serendipity John Cusack leaves it to fate to decide if Kate Beckinsale is the woman for him
They have long been regarded as the perfect movie for a first date.
But according to a study, romantic comedies such as Bridget Jones's Diary and Notting Hill could be bad for your love life.
Rather than being harmless entertainment, 'rom-coms' give people unrealistic – and potentially unhealthy – expectations about real-life relationships, scientists say.
Researchers found that those who watched romantic comedies were more likely to believe in predestined love than those who preferred other genres of movie.
They were also more likely to believe that perfect relationships happen instantly, and were less likely to believe that couples need to work at relationships.
Watching just one romantic comedy is enough to sway people's attitudes to romantic love, they found.
Dr Bjarne Holmes, who led the research, said: 'We are not being killjoys – we are not saying that people shouldn't watch these movies. But we are saying that it would be helpful if people were more aware and more critical of the messages in these films.
The problem is that while most of us know that the idea of a perfect relationship is unrealistic, some of us are still more influenced by media portrayals than we realize.'
For the first part of the study, Dr Holmes and colleagues at the Family and Personal Relationships Laboratory at Heriot Watt University, Edinburgh, studied 40 box office hits from 1995 to 2005 including You've Got Mail, The Wedding Planner, Maid in Manhattan and While You Were Sleeping.
Most of those comedies depicted couples falling instantly in love and promoted the idea of fate – the notion that there is just one perfect mate out there, they found.
'There's a notion of destiny and couples in romantic comedies immediately understand each other,' said Dr Holmes. 'If you think that's how things are, you are setting yourself up to be disappointed.'
In a second study, Dr Holmes asked around 100 student volunteers to watch Serendipity – the 2001 romantic comedy starring Kate Beckinsale and John Cusack, while 100 watched a David Lynch drama.
In a questionnaire after the film ended, students watching the rom-com were far more likely to believe in fate and destiny than those who had watched the 'straight' film.
A third study found that fans of romantic comedies had far stronger beliefs in predestined love.