Films such as Basic Instinct, American Pie and the James Bond movie Die Another Day showed frequent acts of sex between new partners who never give a thought to birth control or the risk of HIV and other sexually transmitted diseases.
A review of the 200 highest grossing films in cinematic history says they are undermining the safe sex and "just say no" messages that underpin public health campaigns. Only one included a suggestion of condom use.
Basic Instinct, released in 1992, starred Sharon Stone whose character seduces the detective investigating her for murder. It included six episodes of sexual intercourse between new and married partners in which no condoms, no birth control measures and no health consequences were shown.
American Pie featured seven sex scenes, all between new partners, with no condoms or birth control and the only unwelcome consequence being social embarrassment.
Hasantha Gunasekera and colleagues, who conducted the review, said the most successful films are now shown around the world and their makers must consider their impact on public health.
"The movie industry influences the perceptions of billions of people. With globalisation and the growth of home-based media technologies, movies are more accessible to a wider audience and there is convincing evidence that the entertainment media influences behaviour," Dr Gunasekera said.
In 98 per cent of the sex scenes studied - 53 episodes in 87 of the films - no form of birth control was used.
None of the films referred to the risks of unsafe sex, such as sexual infection or pregnancy. Instead, they were more likely to depict the social embarrassment of being caught in the act or of being unfaithful.
The authors say in the review, published in the Journal of the Royal Society of Medicine: "Comments made by characters during the movies reinforced promiscuity and ridiculed monogamy and celibacy."
Drug use featured less commonly than casual sex but it too was shown without damaging effects.
Just 8 per cent of the films showed cannabis and 7 per cent other illicit non-injected drugs, always in a positive or neutral light.
Scenes of drunkenness appeared in a third of the films and smoking featured in two thirds. None of the films showed injecting drug use, "perhaps reflecting the target audience," the researchers say.
Three out of four included behaviour potentially damaging to health including unprotected sex between new partners, drug use, smoking and intoxication.
"The regular exposure to unprotected sex with new partners and recreational drug use by influential movie stars in combination with an absence of negative consequence from these actions must be considered in the context of the difficulty experienced by public health advocates in changing population behaviours."
Television producers were more responsible and showed more safe sex scenes. Film producers should learn from television, the authors say.
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