Millions of people in the world have "completely preventable" severe headaches caused by taking too many painkillers, doctors have said.
They said some were trapped in a "vicious cycle" of taking pain relief, which then caused even more headaches.
The warning came as part of the National Institute for Health and Clinical Excellence's (NICE - a special health authority of the English National Health Service) first guidelines for treating headaches.
It is also recommending acupuncture in some circumstances.Prof Martin Underwood Warwick Medical School "Medication overuse headaches" feel the same as other common headaches or migraines.
Studies in countries all over the world 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 NICE 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.
"It is such an easy thing to prevent."
Exactly how painkillers have this effect on the brain is unknown.
Most of the people affected are thought to have started with either everyday, tension-type headaches or migraines. The headaches then became worse as they treated themselves at home.
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.
He said: "This is a huge problem in the population. The figures in terms of the number of people who have medication overuse headache are one in 50, so that is approximately a million people who have headaches on a daily or near daily basis because they're using painkillers."
'Brain gets used to painkillers'
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.
The new guidelines for doctors in England and Wales advise telling sufferers to immediately stop taking all pain relief. However, this will lead to about a month of agony as patients contend with regular headaches without pain relief, until symptoms eventually improve.
The panel said other options for controlling any underlying headaches, such as preventative treatments, could be considered.
Dr Fayyaz Ahmed, the chair of British Association for the Study of Headache, said: "Headache is the most prevalent condition, it puts an enormous burden on the healthcare resources and the economy in general.
Main types of headache
Drugs causing overuse headaches