'I'm back to normal," says Alan. "It wasn't anything really dramatic, just a gradual draining away. But I'm glad it's a condition that no longer means the end of the intimate side of a partnership."
Alan is a 65-year-old former schoolteacher from the north-east who used to suffer from erectile dysfunction. He is rather unusual, because he has tried both Cialis and Viagra, the two main erectile dysfunction drugs on the market.
It is now well known that Cialis's effects last longer than Viagra's - 24 hours as opposed to five hours or so. Less obvious is why this should be useful to anyone other than a gigolo, rock'n'roll animal or sex addict. But Alan is clear on the benefits. "Taking a pill is a statement of intent," he says. "It turns sexual relations into a medical thing." Cialis is different: "It can be taken a day or two beforehand and you can forget about it." In this way, he explains, the sexual act regains its spontaneity.
If Viagra and Cialis have received most publicity, several other drugs are already available or soon will be. One of these is Levitra, manufactured in a venture between Bayer and GlaxoSmithKline and likely to become obtainable on prescription in the UK during the spring.
Dr Geoff Hackett, a GP who specialises in neurology, has been involved in clinical trials of Levitra. He says it is directly comparable to Viagra and acts for a similar duration, but cites significant differences. "It has a slightly quicker time to onset than Viagra. It also has less interaction with food." For example, patients used to a meal with wine as a preamble to sex, can sometimes have a problem with Viagra.
Dr John Dean, secretary of the British Society for Sexual Medicine, welcomes the new addition to the range of impotence drugs. "Patients now have a choice. Each of the three drugs has a different profile, with different side effects."
Impotence frequently involves a shortage of cyclic GMP, a chemical which boosts blood flow into the penis. Its levels are regulated by an enzyme called PDE-5, which breaks it down. The new drugs block this degradation.
PDE-5 inhibitors are not the only medication available. Uprima sneaked on to the UK market last year without the razzmatazz surrounding the launch of Viagra and Cialis. It is the brand name for apomorphine, a substance prescribed in high doses to treat Parkinson's disease. Now it is being marketed as an impotence remedy.
"I've been using it for some time," says Dean. "The attraction is that it works in a completely different way to the others. Uprima actively increases sexual stimulus in the brain. It reduces inhibitory signalling and increases positive signalling."
Uprima targets some of the brain receptors which are normally activated by dopamines. One disadvantage is that is it sub-lingual - it must be left to dissolve under the tongue; this is not so discrete as swallowing a tablet. Furthermore, a small minority of users experience nausea as a side effect.
More importantly, Uprima is not effective for many severely impotent patients. "It is suitable for mild to moderate erectile dysfunction - that is about 80% of GP patients," says Dean. "It is not very effective for chronic sufferers, for men who never ever get an erection."
Another little-publicised substance available on prescription is Yohimbine Hydrochloride, sometimes marketed under the brand name Yocon. The chemical is the active agent of the herbal preparation Yohimbe, an extract of the roots and bark of the West African Yohimba tree.
Cabergoline is another curiosity. Hypersexuality (increased sexual desire) is a side effect of numerous medications used to treat Parkinson's disease. Unfortunately, it can co-exist with erectile dysfunction. None the less, clinical trials of Cabergoline in Germany indicate that this substance can increase male sexual stamina and frequency of orgasm. Yet Cabergoline is neither prescribed for anorgasmia (inability to orgasm) nor actively marketed on the net.
Melatonin is commonly known as anti-jet lag medication but its family of neural receptors has other functions that go beyond the body's internal clock. A medication called Pt 141 targeted at this receptor is likely to appear in the form of a nasal spray within a couple of years.
Apomorphine and Pt-141 are also being touted as remedies for female sexual dysfunction. This is because they act upon brain receptors and not solely on biochemical processes in the genitalia. "Women's sexuality is complex and you need more than a better clitoral erection to enhance their satisfaction," says Dean.
Availability of impotence drugs remains a subject of controversy. Viagra, Uprima and Cialis cannot be prescribed by the NHS other than for sufferers of a list of conditions that include diabetes, multiple sclerosis, Parkinson's disease and prostate cancer. This situation is likely to change only when the drugs lose their patent protection and costs drop; in Viagra's case that will be 2013. In the meantime they are available by private prescription and are heavily marketed on the internet.
In fact impotence remedies are among the most widely demanded of all drugs - legal or illegal. Estimates of the number of men suffering from erectile dysfunction in the UK range from 2-2.5 million.
Yet despite enormous medical and recreational demand impotence drugs are not a universal panacea, as Dean is keen to point out. "Twenty-five per cent of men do not continue using Viagra," he says. "Their sexual function might be returned to them, but the drug is not dealing with any underlying psychological difficulties." Counselling and other kinds of therapy are as important as medication in dealing with impotence.
The Impotence Association: www.impotence.org.uk Helpline: 0208 767 7791
Men's Health Helpline: Tel: 020-8995 4448.
NHS prescription policy: www.doh.gov.uk