Pfizer has explored the idea of selling Viagra without a prescription.

An over-the-counter version of

Pfizer Viagra must be approved by U.S. regulators, who would have to determine that patients could self-diagnose the condition and that the product was safe for use without a doctor's supervision.

Pfizer declined in an e- mailed statement to give details of its plans or a timeline.

Viagra has been used by more than 23 million men since it was approved in 1998, the company has said.

Viagra has been linked with vision loss in some men. The product labeling also carries a warning it shouldn't be taken with nitrates used to treat chest pain.

Since Viagra was introduced in 1998, there has been ongoing speculation about alternative uses and delivery mechanisms of it,'' wrote Pfizer spokeswoman Shreya Prudlo.

As with many of our products, Pfizer has routinely evaluated a number of options (including different formulations, new indications, OTC, etc.) and continues to do so.''

The statement was made in response to a report by a British magazine that Pfizer is developing an oral spray version of genuine Viagra.

Pfizer denied that report.