Viagra maker Pfizer faces stiff competition from generic rivals as patent expires Viagra, used by millions of men to treat erectile dysfunction, loses its patent in the UK on June 21, meaning rival manufacturers will legally be able to produce the little blue pill under its generic name, sildenafil. Use of Viagra in the UK is on the up, with the number of British men prescribed the drug rising to a record high of 2.3m last year, from 1.8m in 2007. Currently a fifth of prescriptions for the drug are issued privately because the NHS has put strict limits on its use at the taxpayer's expense. Pfizer's loss of the patent will mean that the NHS, which spent £40.3m on the drug last year, will make big savings, Generic makers of the drug are expected to slash the price of a pill from £10 to as little as 85p. Viagra was Prifzer's sixth best selling drug last year, generating $2.05bn (£1.35bn) in global revenues, up 4pc on 2011. The company will launch its own cut-price version - Sildenafil Pfizer - in a bid to retain its market share. Sales of Pfizer's highly profitable drug Lipitor, used to tackle high cholesterol, plummeted to $3.95bn last year from $9.6bn in 2011 after the drug lost its patent protection in November 2011. But Jonathan Emms, the company's UK managing director, said Viagra would continue to sell because most people asked for the medicine by name. Mr Emms told the Times: "The brand is very well established and well known among patients." Launched in 1998, Viagra took the world by storm. Ad campaigns were fronted by the likes of Pele, whose insistence he didn't actually need the pills himself led to headlines professing the footballer could "still do keepy-uppy." Actors Michael Douglas and Jack Nicholson have also admitted to using the drug. Last month, Pfizer stepped up fight against counterfeit Viagra, thought to make up 80pc of all of the pills sold online. The company started selling Viagra direct to US customers, where its patent does not expire until 2020, via its own website in May.