Watching porn gives men the unrealistic expectation that it is easy for women to reach an orgasm, a report said.

Researchers at the University of Quebec at Montreal examined Pornhub's 50 most viewed videos of all time to determine the frequency of both male and female orgasms.

They analysed orgasm-inducing sex acts and whether clitoral stimulation was involved, what men and women sounded like when they climaxed and what their bodies were doing when they reached their sexual peak.

Of the videos analysed, 18.3% of women actually had an orgasm, compared to 78% of men.

The study concluded: "As a result, representations of male and female orgasm in mainstream pornography may serve to perpetuate unrealistic beliefs and expectations in relation to female orgasm and male sexual performance."

A number of studies have shown that watching porn can give people unrealistic expectations of sex, and may even put some people off the act.

A study in May said porn can led to erectile dysfunction in men but doesn't affect the sex lives of women.

Men that regularly watch porn are more likely to become disinterested in sex and suffer from erectile dysfunction, a report from the Naval Medical Center of San Diego found.

Addictive

One in five men watch porn three to five times a week and 3% admit they prefer it to sex with a partner, the survey revealed.

Watching porn is addictive in the same way as cocaine, with users building up a 'tolerance' for hardcore content over time that leaves them unsatisfied with real-life sexual activity, researchers said.

Yet, regularly watching porn has little effect on women, they added.

Researchers from the Naval Medical Center of San Diego had 300 male and female patients fill out two surveys on their porn habits.

For men, researchers noticed a strong association between regularly watching porn and suffering from a lack of sexual desire and erectile dysfunction.

Study author Dr Matthew Christman, said: "Sexual behavior activates the same 'reward system' circuitry in the brain as addictive drugs, such as cocaine and methamphetamines, which can result in self-reinforcing activity, or recurrent behaviors.

Higher tolerance

"Internet pornography, specifically, has been shown to be a super normal stimulus of this circuitry, which may be due to the ability to continuously and instantaneously self-select novel and more sexually arousing images."

Watching too much internet porn can increase a person's "tolerance" in the same way as narcotics, Dr Christman said.

Regular porn watchers are less likely to respond to real-world sexual activity and must increasingly rely on pornography for release, he added.