As the news breaks that watermelon is nature’s latest little blue pill, containing citrulline (which relaxes blood vessels, helping to treat erectile dysfunction) most women I know are greeting this development with one voice. “Please, no,” they are crying brokenly. “Not another bloody stamina/libido booster for men!”

Look. I can see that Viagra is wonderful in many ways. As problem pages and the Saga website movingly confirm, Viagra and its stablemate, Cialis, have averted total bed death for many loving couples desirous of “continued intimacy” (the accepted euphemism for a fulfilling sex life). GPs still prescribe it and so they should, even though a doctor told one decrepit specimen who asked for it that it would be like rigging up a flagpole on a disused tenement.

Now the public service/medical/ marital benefits of the drugs have been credited, let’s look at why artificial additives sold at profit, designed solely to match the performance to the libido of the ageing male, might not be such a great idea for both the sexes.

It has led to some of the most heart-sinking chat-up lines recorded. In a hotly contested market, the idea of a wrinkly grandpa growling, “I can satisfy you all night long”, to a pert young thing is retch-making. One female, staying with an elderly bachelor, was startled when her host promised he could “keep it up for hours”, despite needing a stairlift to ascend to his bedroom. All was explained when she grimly spied the Viagra in his washbag.

These drugs have encouraged men to believe that they can all be Hugh Hefner-style playboys well into their anecdotage. (Hef, 82, has declared that Viagra has “freed him to please women sexually” . . . hmm, so much to unpick there, I know, but so little space.)

Viagra is one of the causes behind the surprise increase in sexually transmitted diseases reported last week in the over-45s, although the doubling in sexual disease is attributed to internet dating and the blithe failure to use protection among older couples where pregnancy is no longer a problem.

No, here’s the problem that I reckon Viagra poses for me. Mature women who openly rejoice in their sexuality, such as the divine Helen Mirren, Joan Collins, Catherine Deneuve, Carole Bouquet, et al are rightly celebrated the world over. Respect to these evergreen goddesses.

However, the sad fact is that nature dishes out libido unequally between the sexes. For most mere mortals, the female mojo declines along with fertility. While most women in their fifties, sixties and seventies – according to my scientific adviser Emma Soames, editor at large of Saga Magazine – are flattered beyond words to be found sexually attractive, they do not necessarily pine for Viagra-fuelled rogering marathons.

Frankly, if you have a situation where the woman’s not bothered and just wants to sleep, and the man can do it only with chemical assistance, such epic barnyard activity almost verges on the unnatural.

According to studies, one in three adult women reports suffering hypoactive sexual desire disorder, or “a headache” for short. Which means that the female loss of libido is a common sexual problem and a fairly normal part of growing older.

When I was writing a column on sex for a women’s magazine, the postman would deliver endless packages of peppery oils and topical creams and sprays designed to “correct” it – pep up the female sex drive – all of them useless.

Anyway, let us suppose that the lady in question is very much into it – the canoe’s been put in the water and both are paddling away like mad – but there is still the lingering question of artificiality to be overcome. “Women want a man to be making love to them, not a pill,” Soames points out. “One can’t think of England all night.”

What we have is a gender imbalance. After a point, a man’s libido can hold up (with a lot of help from those magic pills) while a woman’s thoughts might turn to rose gardens and grandchildren. As yet, nothing is licensed for women’s loss of sexual desire. While Viagra was approved 10 years ago, a testosterone gel for postmenopausal women has yet to reach the shelves.

Which is, I reckon, a relief. Not only am I antiViagra, I also think that chemical desire enhancers are a bad idea for both sexes. The contraceptive pill gave women control over their sexuality in 1961. But this was only until 1998 when Viagra was licensed and enabled men to say: you may not feel like it, honey pie, but what am I expected to do about this?

As for a pink Viagra – I worry that as soon as any effective female aphrodisiac is marketed, this would give a retro signal that all women who are not interested have a curable medical condition, which will lead men to offer women – our daughters – chemical inducements to have sex. Which is a ghastly prospect.

According to the psychotherapists, women are much less likely to believe that a pill will magically solve something systemic, such as profound sexual boredom, than men are (which is probably why the drugs companies are not falling over themselves to produce one for ladies to pop like Smarties).

As Phillip Hodson, the psychotherapist and author, told me: “Viagra is socially fascinating. No pill will make a man a better lover, human being, communicator or life partner. We also know that a very large proportion of the partners of men suffering ED [erectile disorder] themselves have sexual difficulties. So simply repairing function in the man does zilch for them as a couple.”

Amen. As it’s all over for Andy Murray for another year, I can’t resist bringing up the rear of Rafael Nadal. Watching at home, I received a text from a girlfriend in SW19: “Am at Wimbledon watching Murray lose,” she said, before giving me the benefit of her eagle eye view of the action on centre court: “Nadal has the most peachy bum!”

Having admired the spindly shanks of McEnroe and Borg earlier in the day, when rain interrupted play and viewers were treated to grainy footage of the finals of yesteryear, I have my own expert commentary on the All England Championships 2008.

Nadal played well and pulverised Murray with consummate athletic dispatch and makes all his opponents look like Mr Puniverse.

There’s only one thing, in fact, that might prevent him from lifting the trophy today: his bum is too big. And his shorts are too small.

rachel.johnson@sunday-times.co.uk

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