The message to Irish men illegally obtaining the new anti-impotence drug Viagra, through the Internet or on the black market, is to be very careful. The deaths of six men in the US and reports that three users in Egypt have been taken into intensive care have put a cloud over the wonder drug, the fastest-selling new drug in the US. Medical authorities and the Garda are advising caution.

But a Pfizer UK spokesman, Mr Steve Buckley, said that as far as the company was aware there was nothing linking the deaths of six men in the US "directly with having taken Viagra".

This week a Dublin clinic was censured by the Department of Health for placing an advertisement in a national newspaper which said "Viagra in Ireland."

A spokeswoman for the Department said it had written to the Wellman Clinic in Eccles Street in Dublin telling it the advertisement contravened regulations since the drug was not licensed in Ireland. It also wrote informing the newspapers.

"Both the clinic and the newspapers agreed to comply," she said. She added that the clinic had advised officials, despite the wording used, that it did not prescribe the drug.

Dr Emad Massoud, medical director of the clinic, denied the advertisement was misleading. "It was a statement, not a promise. What we meant with this ad was the Viagra in Ireland was the Wellman Clinic because Viagra is not yet licensed in Ireland."

Dr Massoud said several patients had turned up in recent weeks with Viagra which they had bought over the Internet. One UK company is selling the blue, diamond-shaped drug for £15 per tablet, and an additional £50 for an on-line medical consultation.

He said there was a "big response" to the clinic's advertisement. It uses various treatments for impotence. "The men ringing looking for Viagra were so much more relaxed. It is much easier to say `I want Viagra' than `I am impotent'."

The chief executive of the Irish Medicine Board, Dr John Kelly, told The Irish Times that regulations forbid the purchase of drugs through the Internet, and this could result in prosecution.

He explained that Viagra is being assessed through a centralised European system. "At the moment it is being evaluated." He expected this to be complete soon. "If it is positive, Ireland will move to authorise in a short space of time."

Chief Supt Ted Murphy, head of the Garda Drug Squad, said there had been no reports of black-market sales of Viagra in Ireland. "We haven't had any complaints at the moment. Maybe it is in circulation but we are not aware of it."

However, he warned men to be careful of buying from anyone offering Viagra. "A lot of tablets are simply manufactured in a lab by these guys and they put a name on them. They are made up to look like a particular tablet so as to cash in."

It is expected that family doctors will be able to prescribe Viagra to Irish men before the end of the year. Some Irish doctors have advised patients to travel to the US and go to a doctor there for a prescription.

Dr T.E.D. McDermott, a consultant urologist, who tested Viagra on Irish men over the past three years with some considerable success, said he had no idea why the six men in the US had died. But as one of the testers he is travelling to the US next week to an investigators' meeting where he expects to hear an explanation.

"They are updating us on the whole thing and obviously the deaths will be the chief concern." He said the men who died may have bought Viagra on the black market, may have taken too high a dose, or may have been on other medication which inter-reacted with Viagra. "Someone with angina may be taking nitrates to open up the blood vessels. Viagra opens up vessels even more and you get a drop in pressure. It would not surprise me that people are dying if they are taking it while on these medications. They forget the side-effects in their enthusiasm."

Other men who decide to take Viagra simply may not be up to sex physically. "The facts of life need to be explained. If you are 60 years old and grossly unfit and Viagra gives you the first erection in five years, that will cause enormous stress."

He emphasised that Viagra improves the quality of an erection but sexual stimulation is needed for an erection to occur in the first place.

"The brain is the whole stimulus of erections in the vast majority of cases. Even with Viagra, unless you have a mental stimulation you will not get an erection. I have had people in already who did not have sexual stimulation but thought Viagra would make them superman. It won't."