The U.S. drugmaker said on Tuesday it was working on plans to launch the non-prescription version of the medicine, known as Viagra Connect, in the United Kingdom in the spring of 2018.
The drug will only be available in pharmacies and its supply will depend on pharmacists' assessment of its suitability for each individual.
Viagra has been one of the pharmaceutical industry's most successful prescription products since its launch in 1998, following a serendipitous discovery of its effects by researchers who had been studying it as a heart medicine.
It achieved peak worldwide sales of more than $2 billion in 2012 but sales have since declined as patents have expired, prompting Pfizer to explore extending its brand value as a non-prescription drug.
Viagra is so far the only erectile dysfunction medicine to be reclassified from "prescription only medicine" to "pharmacy" status in Britain. The change follows a lengthy review by the Medicines and Healthcare products Regulatory Agency (MHRA).
Pfizer will continue to make Viagra available as a prescription drug but the option of also buying it over-the-counter is likely to reduce demand for potentially ineffective and dangerous fakes.
"It's important men feel they have fast access to quality and legitimate care, and do not feel they need to turn to counterfeit online supplies which could have potentially serious side effects," said Mick Foy, the MHRA's group manager in vigilance and risk management of medicines.
(Reporting by Ben Hirschler; Editing by Alexander Smith and Mark Potter)