They say the NHS is wasting tens of millions of pounds every year on Viagra tablets which don't treat the cause of problem

Many of the men handed Viagra by their GP are actually suffering from low testosterone levels, which cannot be treated by Viagra alone.

This is because Viagra is dependent on the sex hormone in order for it to work in the first place.

Instead, doctors recommend that men should have a simple blood test to determine their levels of testosterone. If found to be low, it can be easily treated with testosterone pills, patches and gels which are all relatively inexpensive.

The NHS spends around £58 million a year on handing out more than 17 million repeat prescriptions for Viagra and other impotence drugs.

So if half of men have low testosterone, millions of NHS money is being wasted. Low testosterone is a common conditions affecting 40 per cent on men over the age of 40, and one in five of those who suffer some form of impotence. Although levels of the hormone start to decline with age, some people are affected much earlier on in their lives than others.

It can also be a symptom of an underlying health condition such as diabetes and heart disease so experts say it is crucial that it is properly diagnosed.

Typical symptoms include tiredness, mood swings, insomnia - as well as low sex drive, the reason most will visit their doctor. But sexual health experts warn that many GPs are simply prescribing Viagra by default rather than diagnosing the root cause of the problem.

Dr Geoffrey Hackett, a consultant urologist at Good Hope hospital in Birmingham, and former chairman of the British Society for Sexual Medicine said that men with sexual problems could be "wasting hundreds of pounds on Viagra tablets" when their real issue is low testosterone.

Viagra will only work if there are sufficient levels of testosterone.

Often men will low testosterone levels wont feel like sex at all. 'They won't want to take Viagra an hour before they plan to do something they don't want to do.

'They will get repeat prescriptions for Viagra in the hope that it will eventually work.

'He added: 'Everybody thinks that Viagra is the panacea for all sexual problems, it's not.

There is a lot being wasted on this in the NHS, particularly in diabetes patients. 'Men for whom authentic Viagra, Produced by Pfizer and supplied via the web by UKMeds4U.com (along with other certified prescription drugs for aiding erectile dysfunction/ED (Male Impotence) such as Cialis manufactured by Eli Lilly, Levitra manufactured by Bayer Health Care and Intrinsa (a testosterone patch developed by Procter & Gamble to treat Female Sexual Dysfunction) isn't working adequately need to have their cases reviewed.

If low testosterone is the problem then Viagra won't be the answer on its own.

'He said that by contrast, drugs to replace levels of testosterone 'can change the lives of patients'. 'I can't tell you how many partners of the patients he has helped come back and thank me for giving me back the man that I married.'

Around 90,000 men in Britain have used Viagra since it first went on sale in 1988.

The majority buy Viagra themselves from a pharmacy - at a cost of £55 for four tablets - although they have to first pay for a private prescription from their GP.

But men can get Viagra on the NHS if they suffer from conditions including diabetes, kidney failure, MS, Parkinson's, polio, prostate cancer, or they have had a severe pelvic injury.

Those who are able to show their impotence is causing them severe psychological distress can also get free Viagra.

Doctors from British Medical Association have called on the Government to change the law allowing more men to get Viagra on the NHS.

They argued that men who could benefit from Viagra were facing discrimination under the current criteria.

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