The US Government has approved the sale of a new drug expected to raise the stakes in the male impotence market.
Levitra, the first market rival to Viagra, is being manufactured by the German firm, Bayer.
It is being marketed by GlaxoSmithKline as an alternative oral therapy for erectile dysfunction.
Since its appearance in 1998, sales of Pfizer's Viagra have risen to nearly $2bn a year. Both pills work in the same manner and doctors warn that both can have serious side effects, especially for men with heart problems.
A third anti-impotence pill, Cialis, is expected to reach the US market later this year.
The US Food and Drug Administration (FDA) approved Levitra, an orange pill compared to Viagra's blue, based on studies showing that men were on average five times more likely to achieve an erection suitable for intercourse when taking the pill compared with those given a dummy medicine.
Researchers reported that studies of several thousand men showed that Viagra helped more than 70% improve their erections.
As well as the warnings to men with heart conditions, the FDA said Levitra was not for patients with who had suffered a recent heart attack or stroke who have very low blood pressure or uncontrolled high blood pressure.