The US Food and Drug Administration on Friday approved Allergan Inc's anti-wrinkle injection Botox to treat chronic migraines. Botox injections would be given to adult sufferers of chronic migraines around the head and neck every 12 weeks in an attempt to dull future headaches, said the FDA in a statement.

Chronic migraine sufferers have a headache on most days of the month. Botox has not been shown to work for people who suffer headaches 14 days or less per month, the FDA said. The United Kingdom was the first country to approve the use of Botox for migraine treatment in July.

The approval comes just over a month after Allergan agreed to pay $600 million to settle a federal probe into its marketing practices for Botox. Allergan Inc's shares rose 7 per cent in after-hours trading to $73.90.