LONDON, Sept 18 (Reuters) - U.S.-based drugs group Pfizer Inc said on Friday there was no evidence that its impotence drug Viagra caused heart attacks or strokes.

In response to a letter sent by doctors to the Lancet magazine outlining the case of a 65-year-old Dutch man who died 30 minutes after taking the drug, Pfizer said in a statement:

"To date over three million men have been prescribed approximately 35 million Viagra tablets. This experience provides a consistent picture of the safety of Viagra when used appropriately."

Pfizer noted the doctors writing in the Lancet stated it was unclear to what extent pre-existing coronary artery disease may have contributed to the onset of a heart attack in the patient. "An individual case documenting an adverse event with unclear associated medical information does not provide the basis for
clinical conclusions," it said.

The drug has been the subject of controversy in the U.S, where it has beenlinked to around 70 deaths since its launch in March.

However, the company has said the incidence of deaths is no greater in those taking Viagra than in the target population generally.

The unidentified man featured in the Lancet had been prescribed the drug while in the U.S, and died after taking it on the Caribbean island of Aruba.

Viagra was approved for sale in the European Union on September 15.