It all began 25 years ago in Britain. The UK division of the American pharmaceutical giant Pfizer was running trials on a new drug for the treatment of angina. It was called UK-92480 and it wasn’t pulling up any trees.

But if UK-92480 failed with the heart, the symbolic home of love, it made a big impact on another organ, one with a rather more prosaic association with romance. Male participants in the trials reported a pronounced side-effect: erections. A lot of trees, and other things, were about to be pulled up.

Six years later, on 27 March 1998, the American Food and Drug Administration approved the sale of Viagra and the rest is hysteria. Or at least it was at first. The drug was a phenomenon. It registered sales of $1bn in its first year. And it seemed to drive some people just a little mad.

A chef was arrested in France after serving his customers a dish entitled “beef piccata in Viagra sauce with fig vinegar and fine herbs”. In Taiwan, a prostitute was arrested for killing a 74-year-old client who forced himself on her having already had sex once. And in Israel it was said that four Viagra pills had gone missing during a meeting of a five-member science committee in the Knesset.

Until the arrival of Viagra, the treatment for erectile dysfunction (ED) involved penile pumps or injections, neither of which, perhaps unsurprisingly, ever captured the male imagination. And probably did little for the female imagination either.

Now, suddenly, here was a drug for the problem-solving era, a drug that fitted the impatient acceleration of time in the personal computer age, a drug that, as the joke went, turned your floppy disc into a hard drive.

The research that underpinned the creation of Viagra itself stemmed from the work by three American scientists who would go on to win the Nobel prize for medicine in, coincidentally enough, 1998, the year of Viagra’s birth. The scientists discovered that the body uses nitric oxide to make blood vessels widen. Sildenafil citrate, the compound of which Viagra is the trademark, helps bind nitric oxide to receptors that enable relaxation of the helicine arteries, which, in turn, increases blood flow into the soft tissue of the penis, and results – as long as no one spoils the mood – in an erection.

Last week, it was announced that Britain would become the first country to make Viagra available over the counter. The move was initiated by the Medicines & Healthcare Products Regulatory Agency (MHRA) in the hope that it would prevent men using unregulated websites, where drugs for ED form a large and lucrative black market.

The legitimate market is already, as it were, huge and growing. Prescriptions have trebled over the past decade to almost 3m. But the sales of unlicensed ED drugs remain a profitable and unscrupulous business: among the £50m worth of counterfeit Viagra and other similar drugs seized over the past five years in Britain, some have been found to contain plaster of Paris, printer ink and even arsenic.

Two reasons have accounted for the illegal market. First, the high price Viagra was originally sold at. That dropped significantly in 2013, when Pfizer’s 15-year exclusive patent ran out. The other reason why men have preferred the sometimes dubious anonymity of the internet to the prescriptive dependability of a GP is that if Viagra increases blood flow to the very core of male identity, it’s also a matter that brings blood to the facial cheeks.

Despite the apparent ubiquity of the small blue, diamond-shaped pill, the issue it addresses – impotency – remains a subject of no little embarrassment.

And where there is embarrassment, humour is seldom far behind. When Viagra launched almost 20 years ago, some of the first beneficiaries of the drug were comedians and chatshow hosts. Not necessarily because they were users of it, but because it formed the punchline to so many of their jokes: “Did you hear about the first Viagra overdose? A guy took 12 pills and his wife died.”

By all accounts, Pfizer was a little downhearted that its star turn had become a laughing matter. After all, it had used the conservative figure of Bob Dole, former Republican leader of the Senate, to front its very sober advertising campaign.

But the truth is that while ED is undoubtedly a serious issue, the vulnerability of the penis remains an inescapably comic idea – manhood reduced to the unreliable dimensions of a fickle extremity.

Even celebrity endorsements could not shift the image of Viagra. Hugh Hefner referred to the drug as “God’s little helper”, but then, given that the dressing-gowned one was dating young Barbie-style twins at the time, his approval was never likely to normalise the drug or render it as unnoteworthy as, say, aspirin or indigestion tablets.

David Bailey (79) recently said that he had no problem getting old because Jack Nicholson had introduced him to Viagra. Michael Douglas has also lent his support, calling Viagra a “wonderful enhancement… that can make us all feel younger”. Disinterested observers might note that his wife Catherine Zeta-Jones is 25 years his junior, just as Bailey’s spouse, Catherine Dyer, is 23 years younger than the photographer.

For all their promotional benefits, such testaments ultimately serve to highlight an imbalance: namely that a much younger female partner necessitates a certain chemical help. And yet there are reports of young men taking Viagra to improve sexual performance or to counteract the effects of overexposure to pornography. In both cases, it seems that the effects are perhaps more psychological than physiological. Pfizer has long insisted that the drug has no effect on those who don’t suffer from ED, just as taking an aspirin will have no noticeable effect on someone without a headache.

Anecdotal evidence contradicts this view, but Pfizer points out the increased placebo effect of ED drugs. One executive said that in studies 20% of the men taking a sugar pill placebo reported “rip-snorting erections”. The mind can play tricks, especially on the penis, arguably the most gullible part of a man.

Another aspect of Viagra’s pulsating success story is its name. Rhyming – almost – with Niagara, it manages to conjure up an image of something vital and potent. But originally the brand name, which came out of Pfizer’s “name bank” (made up of invented words that have no meaning in any major language) was assigned to a drug for shrinking swollen prostate glands. It was only because the marketing people didn’t like it for that product that it was returned to the name bank ready for its adoption by sildenafil citrate.

Apparently, another option was “Alond”. A rose by any other name may smell as sweet, but it’s fair to say that that rule does not apply to erectile dysfunction pharmaceutical treatments. Alond is just, well, limp. However, some names you can’t make up, and one of them is Ringaskiddy, the village in County Cork, where Viagra is produced at the chemical plant. Nicknamed Viagra Falls, the village is rumoured to have love, or at least sex, in the air.

Across the water in Britain, the quality of aphrodisiacal air is open to debate, but the distribution of Viagra users is not. Figures show that men in Bradford are more likely to be prescribed the drug, or similar alternatives, than are those from anywhere else in the country. Blackpool comes second. The lowest prescription rates are in Richmond and Kingston upon Thames.

One explanation is a north-south class divide – that health accompanies wealth and the southern middle classes are in a better physical shape and therefore less susceptible to the various complaints that cause ED.

Another is that there is a higher premium on having a good time in the north and that, as the Royal College of General Practitioners has found, an ageing population still expects an active sex life – and just possibly the citizens of Bradford and Backpool are a little less inhibited about asking for it than their countrymen down south.

As they say in the pharmaceutical business, more research is needed. Until then, the only way for the drug formerly known as UK-92480 is up.

THE VIAGRA FILE

Born April 1998 in the US, although conceived six years earlier in the UK.

Best of times It’s been an almost unrelenting success story, although the first year stands out for its billion-dollar arrival - almost unheralded in a new drug.

Worst of times In the early days, 130 people in the US were reported to have died after taking Viagra. Eventually, no causal link was found, but the scare threatened to derail a stunning campaign.

What they say “People are strange when it comes to sex.” David Brinkley, former head of Pfizer’s Team Viagra.

What others say “I like to date a nice range of women each year, but I only use Viagra when I am with more than one.” Jack Nicholson