Almost 200 people around the world have died after taking Viagra, but it has not yet been proven if the drug is directly responsible for the deaths.

Some 130 deaths in the US are being investigated. Five people in the UK and at least 54 others worldwide have died after taking the drug.

Viagra does have side effects. It carries a warning that it should not be used in conjunction with nitrate drugs as combining the drugs could lower blood pressure to dangerous levels.

Patients who ignore the advice put their lives at risk as the drug has been linked to sudden death in such patients with such pre-existing risk factors.

The drug can also affect an enzyme in the retina, causing a temporary blue visual tinge, and has been associated with headaches and stuffy noses.

Latest figures

It emerged last weekend that five people had died following Viagra use in the UK.

Overall it has been linked with 41 cases of adverse reactions between 1 July and 22 December, according to figures from the Medicines Control Agency.

Innapropriate use can lead to heart problems

The reactions ranged from skin rashes to major problems such as heart attacks.

In 11 cases men taking the drug suffered heart disorders, four of whom died. But there is no indication whether they already had heart disease or were taking other drugs for a heart problem. The fifth death was a suicide.

In the US, 130 patients are known to have died after taking drug between late March and mid-November 1998, according to the Food and Drug Administration.

This figure excluded reports referring to "55 foreign patients, 35 with unverifiable information (from hearsay, rumour, the media, or unidentifiable reporters), and 22 with unconfirmed Viagra use".

During the period covered, more than six million outpatient prescriptions - representing about 50 million tablets - were dispensed.

Pre-existing conditions

The FDA said 77 of these men died of heart problems, three had strokes and in the other 48 cases cause of death was unknown.

The other two cases were accounted for by "homicide and drowning".

Excluding the last two cases, the patient died within four to five hours of taking Viagra in 34% of the deaths.

However, most of the patients who died had other risk factors.

The FDA report says: "Ninety (70%) of the 128 patients had one or more risk factors reported for cardiovascular or cerebrovascular disease (hypertension, hypercholesterolemia, cigarette smoking, diabetes mellitus, obesity, previous cardiac history).

"Three additional persons without identified heart disease or risk factors had severe coronary artery disease detected at autopsy."

The FDA updated the label information for Viagra in light of these findings

The label for Viagra in the US and in Europe clearly says that people taking nitrate-based treatments or with pre-existing heart conditions should not take the drug.

Case histories

In September, the Lancet medical journal reported one case where it was thought taking Viagra had caused a heart attack.

The popularity of the treatment means people may be tempted to take too much

The report said that half an hour after taking Viagra, the man began to experience severe chest pains. He has since made a full recovery.

The researchers, led by Dr J Feenestra of the Dutch Drug Safety Unit, said the 65-year-old man's collapse appeared to have been triggered solely by taking the drug.

He had no risk factors for heart attack and had not even had a chance to test the much-hyped drug before his collapse.

Dr Feenestra concluded: "The close temporal relation between ingesting sildenafil [Viagra] and the onset of severe chest pain due to acute myocardial infarction [heart attack]...suggests that sildenafil was causally related."

However, Pfizer, the company that makes Viagra, accused the Lancet of publicity seeking and said that the case reported one heart attack in more than three million users.

Risk factors

Dr Gill Samuels, credited as the inventor of Viagra, spoke to the BBC in December when it was known that there had been 69 deaths in the US and a total of 123 worldwide.

She said: "Unfortunately a number of men have died after taking Viagra. Any death is a tragedy, and we are always concerned when there are reports of serious adverse events associated with the use of any of our pharmaceuticals. But to my knowledge none of these deaths have been directly attributable to Viagra.

"One thing that we have to remember is that we are talking about approximately 130 deaths among over 3,000,000 men who have received Viagra.

"Many of them are older and often have another disease such as heart disease, kidney disease or diabetes. When you resume sexual activity that can actually place a strain on the heart. It is exercise and it does increase cardiac workload."