Everyone knows it as the 'little blue pill' – the fastest-selling drug in history which transformed the sex lives of millions of men.
But treating erectile dysfunction may be just the icing on the cake when it comes to the health benefits of Viagra and other similar drugs.
Experts say another erectile dysfunction treatment, Cialis – a little yellow pill also known as tadalafil – is proving even more effective and may have startling additional advantages for men's health.
Studies suggest it could reduce the risk of heart attacks and treat heart failure. It is already being used in other countries to treat an enlarged prostate – a debilitating condition which affects half of men over the age of 50. And there are promising signs it could even help treat type 2 diabetes and stave off dementia.
In fact, such is the optimism around these pills that some leading experts in men's health say all middle-aged men could benefit from taking them once a day – even if they don't have problems in the bedroom.
Michael Douglas, with wife Catherine Zeta-Jones, has spoken about taking the pills to improve their love life
Professor Geoffrey Hackett, a spokesman for the British Society for Sexual Medicine, says: 'Viagra has become synonymous with treatments for erectile dysfunction, but it's not the only drug and nor is it the most effective.
'It has been overtaken by tadalafil, and every man who is having erection problems in midlife should be taking it. That's because it doesn't just help with erections, but also tackles the underlying problems which lead to erectile issues.
'Moreover, if you give men tadalafil before they have any problems, could you prevent them ever getting erectile dysfunction in the first place, as well as protecting them against heart disease and everything else?
'You may not only be preserving their sex lives and possibly their marriages, but their longer-term health, too.'
As many as half of all men aged 40 to 70 have some degree of erectile dysfunction, according to the British Association of Urological Surgeons – linked to growing rates of obesity, heart disease and type 2 diabetes, which can all reduce the flow of blood to the penis.
No surprise, then, that the latest NHS data revealed a record 4.5 million men are now taking erectile dysfunction drugs.
The Mail on Sunday's resident GP, Dr Ellie Cannon, mentioned this in a recent column – and we were inundated with letters from readers, both male and female, revealing how the medication had given their relationships a boost.
Some were handed the pills after prostate surgery, which causes temporary impotence, or as a result of chronic health issues. But several mentioned they were taking them because of reports they could protect against dementia. Most were on Viagra, but others were particularly impressed by the effects of tadalafil.
One 70-year-old, who had been taking a daily low dose for years, said it had markedly improved his sex life with his wife. 'It makes my erection predictable, firm and constant,' he wrote. 'It removes worry and uncertainty, delivers much more pleasure for both of us and is, to be honest, magic. It's much better than Viagra.'
Many doctors now agree. Marc Lucky, a urologist at Aintree University Hospital in Liverpool, says: 'Viagra is a good starting point for those suffering with erectile dysfunction, but tadalafil has far more bang for its buck.'
What, then, is the difference between Viagra and tadalafil – and why might tadalafil have such promising heart benefits?
Experts say erectile dysfunction treatment Cialis - a little yellow pill also known as tadalafil - is proving effective and may have startling additional advantages for men's health
Crucial to this is understanding what causes erectile dysfunction. The issue is linked to reduced blood flow into tiny arteries which feed into the penis. This can be caused by a range of medical conditions which develop with age.
They include high cholesterol, which clogs the arteries, and heart disease which affects how well blood is pumped around the body.
Type 2 diabetes, linked to too much body fat which causes high blood sugar, can also reduce blood flow to blood vessels and nerve endings. Obesity is also linked to the condition, although the association is more complex. It is thought to damage the blood vessels, affecting blood flow to the genitals, but excess fat also reduces levels of the male sex hormone testosterone, which is linked to strong erections.
'The artery to the penis is just one example of a blood vessel that isn't functioning,' explains Prof Hackett. 'It just happens to be the one that's most obvious. To my mind, a man of a certain age presenting with erectile dysfunction is a cardiac patient unless proved otherwise.'
Experts say if obesity is an issue, lifestyle changes alone could improve erections. If you do need drugs, however, Viagra and tadalafil work differently.
Viagra needs to be taken immediately before sex, and the effects last for three to four hours.
But tadalafil stays in the body for longer and is intended as a regular once-a-day pill. The effects last 36 hours – which is why it is sometimes described as 'the weekend pill' – and should mean you can get an erection when you want one.
Hollywood actor Michael Douglas, 79, has previously spoken about taking the pill to improve his love life with wife Catherine Zeta-Jones, 54.
'Some wonderful enhancements have happened in the past few years – Viagra, Cialis – that can make us all feel younger,' Mr Douglas said in 2010.
Experts agree that tadalafil is a modern marvel.
'It removes the tablet-taking from the sex – women tend to hate orchestrated sex, that wink to say you've taken a tablet and it's time to go upstairs,' Prof Hackett says.
'When men are healthy, they get erections all the time. We should be seeking to normalise that, not settle for what was – 25 years ago – the best we could do, which was with Viagra.'
It also means the impact on blood flow is more sustained – and it is this which leads to the additional health benefits.
Erectile dysfunction pills have transformed the sex lives of millions of men around the world
'If you use drugs that increase the blood flow through the arteries to the penis, they'll also improve the blood flow to your coronary arteries,' Prof Hackett adds. 'Tadalafil works better because the drug is in your system 24/7. Imagine the doctor giving you high blood pressure tablets and asking you to just take them when your levels are high – it's nonsense and wouldn't work.'
One US study which looked at the medical records of men with erectile dysfunction found those who took tadalafil most often had the lowest rates of heart problems. It was also linked to fewer heart-related deaths.
Another study, funded by the British Heart Foundation, found tadalafil could slow or even reverse the progression of heart failure in sheep – and the researcher, Prof Andrew Trafford at the University of Manchester, has argued that the effect was likely to be similar in humans.
He says: 'It's entirely possible that some patients taking it for erectile dysfunction have also unwittingly enjoyed a protective effect on their heart.'
Further work carried out by his team has found Viagra may prevent arrhythmias occurring in the heart – irregular heart rhythms which kill around half of people with heart failure.
And soon to be published research carried out by Prof Trafford and his team also suggests tadalafil can prevent and even reverse the thickening of heart muscles linked to sudden cardiac death and heart failure.
'It's entirely reasonable to ask whether men in midlife would benefit from taking these drugs routinely,' he says.
The BHF has also called for further research. Experts do not believe that tadalafil will ever be a replacement for existing heart drugs, such as statins. However, they say it is possible that the erectile dysfunction drug could be combined with these other treatments to further improve the health of men.
Prof Hackett also believes 'every man with type 2 diabetes' should be taking the drug, and also those with prediabetes – elevated blood sugar which is not yet in the diabetic range.
This is because studies have found tadalafil increases blood flow to the liver, which allows it to absorb and store more sugar from the blood, reducing levels of sugar which circulate around the body and cause damage.
It also increases blood flow to other parts of the body affected by diabetes, such as the feet, which can otherwise end up so damaged – known as diabetic neuropathy – they have to be amputated.
'If someone with diabetes isn't getting enough blood to their penis to get an erection, you can bet their feet are affected as well,' Prof Hackett says. 'Tadalafil is actually a very good treatment for diabetic neuropathy.'
It is also licensed in Europe, parts of Asia and in the US to treat an enlarged prostate, known as benign prostatic hyperplasia, or BPH. One in four men suffer from this condition at some point as they age, which is caused by the prostate enlarging and pressing on the bladder and urethra, the tube along which urine exits the body.
The UK's medicines watchdog, the National Institute for Clinical Excellence (NICE), looked at it for this purpose in 2013 but could not proceed because no evidence was received from the drug's maker, Eli Lilly.
Some private doctors in the UK will prescribe it for an enlarged prostate, however.
Prof Hackett says men who don't have underlying health conditions could benefit from tadalafil as a preventative measure. But he adds: 'If you wait until a man's got erectile dysfunction, you need to assume he's probably had it for a few years before he approached a doctor.
'The arteries of the penis are very small and start showing symptoms of being blocked three to five years before the coronary arteries do. By the time a man sees a GP about their bedroom problems, the disease process elsewhere in the body will have progressed. We should be doing a study to see what happens if you give it to men before problems start.'
Generic versions of Viagra, known as sildenafil, can be prescribed without restriction on the NHS, and can be bought at pharmacies without seeing a GP.
But while one form of tadalafil – Cialis Together, a tablet designed to be taken 'on demand' like Viagra – can also be bought without a prescription in some pharmacies, guidance from NICE means tadalafil for regular use can be obtained only on prescription.
Only men with erectile dysfunction linked to specific conditions including spinal cord injuries, multiple sclerosis and prostate cancer can get it on the NHS. This guidance has not been revised since the drug's patent expired in 2017, making it significantly cheaper. Previously a month's supply cost the NHS £55 per patient – today, it's £3.
'NICE and many GPs don't seem to be aware of that,' Prof Hackett says.
'For a daily £3-a-month pill, men wake up with erections and are back to the way they were.'
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Rise and rise of the little blue pill that 30 million men now rely on
A group of British scientists working at US drugs giant Pfizer accidentally stumbled across the effect for which Viagra became famous.
They were researching a drug called sildenafil citrate which they believed would be useful in treating high blood pressure and angina – chest pain linked with heart disease – they noticed a startling side effect: men taking it were getting erections.
The trials quickly switched tack as Pfizer realised it had a multi-billion dollar blockbuster on its hands.
Viagrahit the shelves in 1998 and featured on the cover of Time magazine
Viagra hit the shelves in 1998 in a blaze of publicity, with pharmacists dispensing tens of thousands of prescriptions for the distinctive little blue pills in the first weeks alone. It even featured on the cover of Time magazine and had a starring role in hit drama Sex And The City. Annual sales reached £1.4 billion by 2008.
Other companies rushed to develop similar drugs, and tadalafil, under the brand name Cialis, was released in 2003 promising a longer duration of action and more spontaneity.
Today there is also Levitra (vardenafil) which may have fewer side effects for some men than Viagra, and Spedra (avanafil) which works in as little as 15 minutes.
It's estimated that about 30 million men worldwide now use the pills regularly – and around 17 per cent claim that they saved their relationship.
