The move will improve the sex lives of millions of men in a country where the contraceptive pill is still unavailable for women.

Pfizer, the company that makes Viagra, applied for the licence in July last year.

The swift decision contrasts with the Japan Ministry of Health and Welfare's position on the contraceptive pill, which has been available in Western countries since the 1960s.

Demand

There is expected to be huge demand for the drug in Japan, as there has been in every other country where Viagra is available.

In the UK the drug will only be available to patients falling into certain categories. The government placed restrictions on NHS prescriptions of Viagra in an attempt to limit the cost of the treatment to the UK health service.

In Japan it is estimated that six to seven million men suffer impotence. They will only be able to get Viagra with a prescription.

A spokesman for the Japan Ministry of Health and Welfare said: "We have approved it after concluding there is no problem on safety and its effectiveness.

"There is strong demand from patients here since there is no drug like Viagra in Japan.

"Given the high popularity of the drug, we have also urged stores to take precautionary measures against theft."

Pill concerns

While men can now get hold of the heaviest-hyped drug of the 1990s, the prospects look slim for Japanese women getting the pill enjoyed by their Western counterparts since the 1960s.

"We are still in the midst of discussions, and don't know how long it will take for us to approve the pill," the spokesman said.

"One of the concerns is that if we allow the pill, it will cause further spread of sexually transmitted disease such as Aids and the other is about the pill's side effects that include causing cancer," he said.