Supplies of the American made drug reportedly sold out within hours of going on legal sale, forcing pharmacies to call for new shipments.

One chemist in Rio de Janeiro said he found two men waiting outside his shop when he opened for business at seven o'clock in the morning.

Viagra is only available in Brazil with a doctor's prescription.

But according to BBC correspondent Liz Throssell in Miami a black market has been flourishing.

Sex boasts

Israel banned imports of the pill until more was known

The correspondent said Brazilian men often joke about their sexual appetite - and prowess. It is therefore not surprising that Viagra has awakened such interest in the country.

A box of four pills costs around $50 - a lot of money for many Brazilians. But it seems the stimulus attributed to Viagra knows no price.

The huge demand has already led to a flourishing black market, with people smuggling Viagra in from neighbouring countries like Bolivia and Paraguay, and then re-selling it for around $700.

'Drug safe'

The drug's makers, Pfizer, insist it is safe. But in the excitement surrounding the pill, it seems some men have been taking Viagra without medical supervision.

At least two Brazilians, who were also being treated for heart problems, are said to have died after using the drug.

The correspondent said such indiscriminate use worried the Brazilian authorities so much that they were forced to bring forward Viagra's official launch.

But with reports in the local media calling it an elixir of youth and happiness, some Brazilians might be tempted to overdose in the pursuit of pleasure.

Deaths reported

At least six men have died after taking Viagra but it is not clear whether any of the deaths were caused by the drug.

Others have reportedly been hospitalised.

The US Food and Drug Administration (FDA) said it and Pfizer were investigating the causes of the deaths.

The FDA said the deaths had been reported by Pfizer as part of routine reporting requirements.

Meanwhile, the Israeli Government has lifted its one-week ban on Viagra, following clarification from the US FDA about the deaths.