The announcement, from the United States’ Food and Drug Administration, means that Levitra, an orange pill, will give men an alternative to Pfizer Inc's famous diamond-shaped blue pill Viagra, the drug that transformed treatment for erectile dysfunction after its 1998 debut as the first oral therapy for the condition.


Another competitor, a pill called Cialis, may also hit the US market later this year.


An estimated 30 million US men experience some level of erectile dysfunction.


"We know, from considerable market research, that the market is ready for new options," said Lawson Macartney, head of strategic management of GlaxoSmithKline's cardiovascular, metabolic and urology drugs. 


"We know, from considerable market research, that the market is ready for new options"

Lawson Macartney, head of strategic management at GlaxoSmithKline

Levitra, Viagra and Cialis all work by blocking an enzyme called PDE-5 which affects blood flow to the penis, but the potency, speed and duration of each drug are hotly disputed.


Levitra's makers say a major plus is that it works quickly. Men taking Levitra can have an erection in 16 minutes, and any time after that, up to five hours later.


Pfizer has responded with studies showing half of men taking Viagra were able to have sex within 20 minutes.


Trials of Cialis, from Eli Lilly and Co and ICOS Corp , show it gives patients a window of up to 36 hours in which to have sex. The window is about four hours for most men taking Viagra.


Levitra's most common side effects include headache, flushing and nasal congestion.


The most common side effects from Viagra are headaches, flushing and stomach upset.