Up to a million people in the UK have "completely preventable" severe headaches caused by taking too many painkillers, doctors said. They said some were trapped in a "vicious cycle" of taking pain relief, which then caused even more headaches.

There is no definitive UK data on the incidence of the condition, but studies in other countries suggest 1-2% of people are affected, while the World Health Organization says figures closer to 5% have been reported. While painkillers would be many people's instant response, they could be making sufferers feel even worse. Prof Martin Underwood, from Warwick Medical School, who led the panel, said: "This can end up getting into a vicious cycle where your headache gets worse, so you take more painkillers, so your headache gets worse and this just becomes worse and worse and worse.

Manjit Matharu, a consultant neurologist at the National Hospital for Neurology and Neurosurgery, said there was a tipping point at 10 to 15 days of using pain relief each month when the drugs became the issue. People with a family history of tension-type headaches or migraine may also be genetically more vulnerable to medication overuse headaches. They could be susceptible when taking pain relief even if it is not for headaches.