Porn causes erectile dysfunction in men but doesn't affect the sex lives of women, new research reveals.

Men who regularly watch porn are more likely to become uninterested in sex and suffer from erectile dysfunction, the study found.

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

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

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

Researchers from the Naval Medical Centre of San Diego had 300 male and female patients fill out two surveys on their porn habits, the Daily Mail reports.

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 behaviour 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 behaviours.

"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" the same as narcotics, 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.

Pornography may also set up unrealistic expectations in young and inexperienced men, said Dr Joseph Alukal from New York University.

This could cause libido-sapping anxiety when real-world sex doesn't measure up to filmed fantasies, he said.

It is unclear why the effects do not also occur in women.

The findings were presented at the American Urological Association's annual meeting in Boston on Friday.

This comes after researchers from Brigham Young University, Utah, found that self-proclaimed porn addicts may struggle to secure and maintain romantic relationships.

Porn use was not linked to relationship anxiety among those who described themselves as having a healthy habit.