Botox is licensed to prevent headaches in adults with chronic migraine, but the National Institute for Health and Clinical Excellence (NICE) said on Thursday the company had not provided sufficient evidence to prove its value.

Without additional information NICE said it was inclined not to recommend Botox as a migraine treatment option in the state-run health service. The agency's draft guidance is open for comments until March 8.

Allergan said in a statement it was "working constructively" to address key questions raised by NICE and would be submitting a revised economic model.

"Allergan believes that the revised model presents robust evidence demonstrating that treatment with BOTOX is both a cost-effective and clinically meaningful treatment option," it said.

• A Permanent Economic Emergency