Viagra - it is the drug that has transformed the lives of millions and changed the way we think about sex forever.
By Adam Harcourt-Webster
BBC Money Programme
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The rise and rise of Viagra has created a £1.5bn worldwide market in anti-impotence pills.
Now rivals are fighting for a share of the spoils and it is becoming a recreational drug of choice for some in the party generation.
Last week, Pfizer's chief executive Henry McKinnell warned that Chinese made counterfeits posed a threat to its business and urged the country's authorities to clamp down on the copycats.
Pfizer, the world's biggest pharmaceutical company, stumbled on the drug by accident at their research labs in Sandwich, Kent.
In the late 1980s, they had been developing a new treatment for angina, but noticed a strange side-effect in trials - increased erections among volunteers.
The effect on their sex lives was so marked that once the angina trails were over the volunteers wanted to keep on taking the medication.
Pfizer decided to commission some new research.
In 1989 they approached Clive Gingell, one of Britain's top Urological Surgeons, based in Bristol.
He had spent his whole career trying to treat and improve the lives of thousands of men suffering from impotence.
In those days, commonly used treatments included the fitting of implants directly into the penis, a vacuum pump and self injection.
Most sufferers were thoroughly put off and consigned themselves to a life without sex.
Mr Gingell ran a new series of trials, and the results impressed him.
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He describes Viagra as "a wonder drug".
"The thought of having a pill that would cure impotence was amazing to me," he says.
"I never thought I would see it in my lifetime."
"There has been a kind of Holy Grail idea associated with curing impotence," Pfizer's Mariann Caprino tells the Money Programme.
"And here it was in a little blue pill."
When Viagra was launched in 1998, Pfizer's share price doubled. It was apparent that there was a huge previously untapped market out there.
Doctors claim that half of all men over 40 become impotent at some point in their lives.
That is more than 150 million worldwide, with two million sufferers in Britain alone, so the potential market for drugs like Viagra is colossal.
Overnight Viagra made Pfizer famous. "We discovered the mass production of penicillin, yet it was Viagra that put Pfizer on the map," says Ms Caprino.
Nevertheless, despite the highly successful launch, the company faced a huge potential problem in selling Viagra.
Men were simply not willing to talk about impotence, they were ashamed.
If they were not prepared to discuss their impotence, how could they be persuaded to ask their doctor for a prescription?
Ray Reynolds, who suffered from impotence for 30 years, had simply given up hope of ever being able to have sex again.
"I thought well, I'll just put it to one side and remain a eunuch for the rest of my life," he says.
To overcome the problem, Pfizer came up with a series of marketing ploys.
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Firstly, they asked the Vatican, and other world religious leaders, for their blessing. This headed off possible moral and religious objections.
Secondly, they employed big name celebrities to encourage men to seek treatment for impotence.
Pele, the legendary footballer, headed a men's health campaign about erection problems, and 75 year old former US Presidential candidate Bob Dole went public for Pfizer about his own impotence problem.
American men rushed to their doctors.
Leon Steinberg, an 84-year-old impotence sufferer living in a retirement community in Florida, was impressed by Mr Dole's courage in coming forward.
"When I saw it on TV, I admired him for it," he says.
"You might say he was my idol."
Withdrawal of campaign
Pfizer decided not to use the term "impotence" in the advertisements, instead replacing it with a more bland technical term "erectile dysfunction".
Pfizer's Mike Suesserman says the new term "allowed us to make the condition a household name".
Pfizer reasoned that few men may admit to impotence, which employs a complete loss of ability, but a lot more may own up to erectile dysfunction, which suggests a much broader range of symptoms.
But Pfizer's aggressive marketing campaign has recently run into trouble.
A recent television advertisement has been criticized in the United States for suggesting that Viagra might be better and more effective for patients than the clinical experience suggests.
The Food and Drug Administration ordered its withdrawal.
There are potential problems, too, in the increasing use of Viagra as a recreational drug.
Half of all men over 40 become impotent at some point
"For a lot of gay people it is just a normal way of life," says Gary Mercado, who runs the Elysium Resort, the largest gay hotel in Fort Lauderdale, Florida.
When Viagra is taken with amphetamines, "you forget about having protective sex, so there are huge capabilities of transmitting all sorts of sexual diseases", he says.
Pfizer says that a very small percentage of people abuse Viagra, but accepts there is great potential in developing the market for sexual pharmaceuticals.
Meika Loe, author of the book The Rise of Viagra, agrees: "In the Viagra era, sexuality is subject to the cult of efficiency. It's become almost McDonald's-ised. Serve it up fast and hot."
The Money Programme: Viagra: The Hard Sell was broadcast at 2200 GMT on Wednesday, 9 February on BBC Two .