Leading US relationship advisor Dr Phillip McGraw has hit out at users of internet porn, insisting that it is cheating on their partners.

McGraw, who offers advice to millions of Americans on Oprah Winfrey's TV show, said that women should not put up with their partners looking at web porn, which he described as an addiction.

"Addicts give lame justifications for their behaviour like: 'It's harmless', or 'Everybody's doing it'. By doing this, they ignore the effect their problem is having on the people around them," he said.

With more than 17.5 million users visiting internet porn sites from their homes every month, McGraw's statement could result in more domestic confrontations.

"This behaviour is not OK, it's not even almost OK. This habit is a perverse and ridiculous intrusion into your relationship," he advised partners of porn 'addicts'.

He told people not to put up with excuses such as 'All men look at porn', or 'It's just the internet'.

This attitude speaks volumes about the health of the relationship, he said. A partner has to choose what's more important to them: pornography or the relationship.