A growing 'ladette' culture of women who prefer instant action is proving so intimidating that more and more young men are taking the blue pill to cope.

The claim comes from Ireland's leading psychosexual therapist, who says that in the past year she has met a growing number of anxious young males who complain they are expected to "perform at will".

Mary O'Conor says the rising number of women who want instant gratification within hours of meeting a man is leading to immense pressure to perform between the sheets.

"There is a certain group of women who are ladettes and they are just out to have a good time," says Ms O'Conor. "They want to have sex and they don't want any strings attached.

"They say that they give guys the wrong number or that they don't give them a number at all. It's a bit like what would have been traditionally viewed as 'the stereotypical lad'."

The Dublin-based sex therapist says women are now more vocal than ever about their demands and that this pressure is forcing some young men to turn to the erection-enhancing drug for help.

"For guys who are not very confident, they find it difficult when they are expected to perform at will on the first night, which can lead to problems.

"They can become very anxious and this in turn can lead to a situation where they are again apprehensive the next time they're with a girl. So it's a whole other aspect of erectile dysfunction that we're seeing now."

However, men as young as their late teens are now plucking up the courage to seek professional help.

"I am seeing men who are as young as 19," says Ms O'Conor. "Certainly 20 and 21-year-old guys [who are coming to see me] would be taking Viagra or Cialis.

"These guys sometimes feel that they should be able to perform at will and I'm trying to reassure them that they shouldn't.

"There should be some element of the chase and there certainly should be some element that they fancy the girl and they should certainly know her. But unfortunately the natural order of things is being side-tracked."

A recent survey carried out by the Erectile Dysfunction Information Bureau revealed that men consider impotence to be the most embarrassing medical problem to discuss with a doctor.

The study found that only 10 per cent of men who experience impotence ever seek medical help.