BBC's Horizon explores the history of impotence

Scientists say the arrival of impotence wonder drug Viagra is just the beginning of a long process of change, particularly for women.

Pfizer, its manufacturer, is currently conducting research to find whether the first oral impotence drug can stimulate erections in women.

Research in the UK suggests a third of women complain of a lack of sexual desire, a quarter have difficulty achieving orgasm and one in six say sex is painful.

Researchers at the University of Maryland in the USA are trying to find out more about the science of sexual arousal in women.

Female anatomy

In a BBC Horizon programme on Viagra, called "Sexual Chemistry", Dr Jennifer Berman, a urologist at the university, said she had often wondered why most of her impotence patients were men.

Dr Jennifer Berman: confronting ignorance on women and sex

"I wanted to know why we did not have the same understanding of female anatomy as men.

"Is it that we do not care, that we do not want to know, that we feel uncomfortable? It was not clear what the problem was."

Her research suggests that the chemicals involved in arousal in vaginal tissue are similar to those in the penis.

Like men, women with heart problems, high blood pressure, diabetes and other conditions are likely to have problems achieving erection.

However, she admits there is a lot about women's sexual physiology that is unknown.

Arousal

An Australian study earlier this year suggested the clitoris was much larger than had previously been thought.

It said this resulted in doctors doing operations such as hysterectomies cutting nerves that are important in sexual arousal.

In the summer, specialists in the field of female sexual dysfunction met in the USA to look at how to define the problem.

At least 12 other drug companies with impotence pills in the pipeline attended the conference.

Ellan Laan, a psychologist at the University of Amsterdam, is one of the pioneers in the field.

She is investigating what women feel when they are sexually aroused.

Her research, which involved monitoring genital blood flow when women were watching erotic films, showed that women responded to sexual stimuli automatically.

"Response occurs without them being aware of it, even without them wanting it," she said.

Scientists say they need to know not only the way women respond to sexual stimuli, but how they perceive their response in order to know what kind of drug they would want.

Out of the closet

Even though there is less research on impotence in women than in men, with women who have sexual problems often being classed as "frigid", it is only fairly recently that male erectile dysfunction came out of the closet.

Men, particularly older men who are more likey to suffer from impotence, were treated as if it was their fault, that it was all in the mind and that they should try to accept their sex life was more or less over.

Robert Dickinson's drawings of sexual anatomy broke old taboos

Among the pioneers in the field was US physiologist Robert Dickinson who, in the 1940s, attempted to catalogue male and female sex organs.

He created a picture of the average couple, Norma and Norman, as well as taking 1,000 photos of erect penises and measuring them.

Another pioneer was tyre seller Geddings Osbon from Georgia, USA.

He was told to accept his sexual years where over, but he refused.

Instead, he used a pump and fitted a tube from it to his penis.

He put an elastic band around his penis to restrict blood flow out of it and pumped.

His "research" led to the creation of vacuum therapy.

Injections

Sixteen years ago, a British neuroscientist injected himself with a drug which caused an erection and displayed his success at a conference in Las Vegas.

The result caused a sensation. Scientists had not believed it was possible to reverse impotence by injecting drugs into the penis.

The discovery of a drug that could be injected into the penis was a big step forward

They believed drugs would cause the penile muscle to contract, but in this case it relaxed and expanded.

As research methods improved, it became absolutely clear that impotence was not just a psychological condition.

Ultrasound showed the impact conditions such as thickening of the arteries and diabetes could have on the penis. And then came Viagra.

Scientists began developing the drug 12 years ago in Sandwich, Kent.

They were looking for a pill which could treat angina, but they found that Viagra had unforeseen side effects - it caused erections in men by relaxing the penile muscle and increasing blood flow.

By 1991, they knew they were onto a drug which could treat impotence, but they needed to do more research into what triggered arousal.

They drafted in 1,500 staff to develop the drug and sank �350m into it over a staged period.

A discovery in Los Angeles gave their research a big boost and provided the last link in the erection chain.

Scientists found that nitric oxide was the chemical which transmitted sexual arousal messages from the brain to the penis.

Viagra blocked the work of the enzyme which was the last stage in arousal.

Meteoric rise

Gill Samuels, director of early clinical research into Viagra, said: "We felt like we were right on the cutting edge of science."

Other research was carried out to find out how long Viagra erections would last, using a rigascan, to measure rigidity, and weights.

Most men on Viagra had 80% rigidity for an average 10 minutes.

The last part in the history of Viagra's meteoric rise came four years ago when research showed the extent of male impotence.

A US study showed more than half of men surveyed had been impotent to some degree and one in 10 were totally impotent.

Viagra showed that impotence was not all in the mind, although anxiety about sex releases hormones with contract the blood vessels, so creating a vicious impotence cycle.

Side effects

However, the drug does have side effects. It carries a warning that it should not be used in conjunction with nitrate drugs as combining the drugs could lower blood pressure to dangerous levels.

It can also affect an enzyme in the retina, causing a temporary blue visual tinge.

Over 100 men around the world are believed to have died after taking Viagra.

But nothing seems to stop its rise. More men have been to their GP about impotence in the USA in the last three months than in the last five years.

British doctors fear the same may be the case in the UK where Pfizer is set to make around �100m a year.

If it works on women as well, that figure could double.