Health correspondent James Westhead: "Impotence sufferers and doctors confused"

The EU's Industry Commissioner Martin Bangemann signed authorisation for the drug on Tuesday morning, but said the drug should only be available on prescription.

The signature was part of a six-month approval process, which included a scientific assessment by the European Agency for the Evaluation of Medicinal Products and clearance from its committee of experts and a standing committee of representatives from all 15 member states.

However, it is unclear how many governments will agree to pay for Viagra.

Around Europe

The UK has decided to ban the prescription of Viagra on the NHS until it can decide on how to ration the drug, which could cost up to £100m.

In France, Viagra will be available on prescription from October, but patients will have to pay for the drug, which will cost $10 a pill.

Impotence sufferers in Germany, Italy and Denmark will also have to pay for their own treatment, although Germans with private medical plans will be able to claim the money back.

However, in Austria, the drug is likely to be paid for from the social security budget.

Safe

Patrick De Boyser: Viagra is safe and effective

Patrick De Boyser of the European Commission said the drug had been found to be safe and effective.

He stressed: "It is a medical product treating a condition, erectile dysfunction."

However, he added that demand for the drug was likely to be high across Europe and there were "serious concerns" in several countries about funding the cost of it.

The EU's body of pharmaceutical experts - the EMEA - cleared the way for approval of Viagra in August when it voted to approve a European marketing licence for the revolutionary drug.

Best-selling drug

Viagra has become the fastest-selling new medicine since its launch in the US in April.

Patrick De Boyser: Viagra is a medicine like any other

However, over 100 deaths around the world are being investigated in connection with the drug.

In the US, most of the people who have died are thought to be elderly people with heart problems and over two million people have taken the drug without problems.

The EU says Viagra should not be prescribed for women, people under 18, those who have had strokes or heart problems, people with low blood pressure and those with liver problems.

People with other conditions, such as leukaemia and sickle cell anaemia, are also advised that the drug could be an additional health risk.

The EU recommends that Pfizer warn of the drug's possible side effects, including headaches and painful, prolonged erections.

Pfizer, which plans to have the drug available for sale in the next two to three weeks, already warns that Viagra should not be taken in conjunction with nitrate-based drugs as it could lower blood pressure to dangerous levels.