As sales of Viagra double, we reveal the UK's hotspots of the sex drug Sales data from the past 3 years shows Liverpool, Coventry and Glasgow men are also big users of the sex-enhancing drug Since Viagra went off-patent last month, pharmacies have noticed a surge in sales as cut-price versions of the drug have flooded the market It is many men's little secret, but research has finally revealed the top ten Viagra sales hotspots in the UK. It found that Belfast reported the highest sales of the sex-enhancing drug, followed closely by Slough and Portsmouth. The news has coincided with new figures showing that sales of the little blue pill have doubled since it went off-patent and became 75 per cent cheaper last month. Scroll down for erectile dysfunction calculator New research has shown where the top 10 Viagra sales hotspots are in the UK. Belfast is in pole position while smaller towns including Chester and Norwich have also made the list Research into sales differences across the nation analysed data collected over the past three years. Statistics collected by ChemistDirect.co.uk found that sales peaked in Northern Ireland's capital. It also revealed that small towns such as Chester and Norwich made the top ten, as did Maidenhead, a popular area for the over 50s. 1 Belfast 2 Slough 3 Portsmouth 4 Glasgow 5 Coventry 6 Chester 7 Leicester 8. Liverpool 9 Maidenhead 10 Norwich Viagra was formulated by pharmaceutical company Pfizer and was launched as a sex-enhancing medication in Britain in 1999. It was originally developed to treat high blood pressure and angina but was found to be ineffective for these conditions. However doctors noticed it led to sustained erections, as a result of temporarily increasing blood flow to the penis. Last year 2.3 million British men were prescribed the drug, costing the NHS £40.3million. But last month the manufacturer of Viagra lost its exclusive right to make the drug. Since then, the price of the sex drug has dropped dramatically and could drop as by up to 90 per cent, taking the cost of a pill from £10 to £1. Over 20 manufacturers have applied for a license to produce a generic version of the drug, whose chemical name is sildenafil. The drug is so commonly used that stars including Michael Douglas, Jack Nicholson and Hugh Heffner have openly admitted to taking it. Until the drug went off-patent, NHS cuts had made it difficult for men to get the medication, with only men suffering with diabetes, multiple sclerosis and prostate cancer being offered it. But since then, legally produced sildenafil has flooded the market, triggering a 75 per cent drop in the price of the pills Because of this a fifth of all prescriptions last year were private. But since then, legally produced sildenafil has flooded the market, triggering a 75 per cent drop in the price of the pills. One online clinic, DoctorFox.co.uk, has seen a doubling of orders as more men request treatment and can afford to buy greater quantities. The clinic's price for four 25mg pills of sildenafil has plummeted to £6.60 compared to £24.20 in June. Calculate your risk of erectile dysfunction with the quiz designed for MailOnline by online GP service DrEd.com.