Viagra - the fastest-selling drug yet

Along with Pfizer's Viagra, other drug companies, including Bayer and Eli Lilly, have now jumped on to the impotence bandwagon with their own solutions to the problem.

Viagra still has the lion's share of the market and is used by 20 million men in 110 countries.

However, Cialis is grabbing an impressive share, boasting 14 per cent of the UK market only months after its launch.

Now, four years after its introduction, it is possible to get behind the headlines that proclaimed Viagra as the ultimate wonder drug for men and see what it will and won't do.

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