Overuse of common over-the-counter painkillers can cause chronic headaches, according to an ongoing Swedish study.
Women are shown to be the worst hit by the problem with the chronic headaches three times as likely than among men.
"We usually call this a paradox. We don't know for certain what the reason is, but taking medicine more that ten days per month over at least three months carries a greater risk of being afflicted," said Pernilla Jonsson, a researcher at Gothenburg University, to the Dagens Nyheter newspaper.
The study, which has been funded by state pharmaceutical chain Apoteket AB's research fund, has looked at a sample of 45,000 randomly selected people who have been questioned over their use of pain killers and incidence of headaches.
150,000 people are reported to suffer from chronic headaches in Sweden, the newspaper writes.
According to the results of the study so-called triptans, used for the treatment of migraine headaches the 1980s, tend to cause the most rapid onset of chronic headaches, while regular medicines such as Alvedon are the most common cause.
The researchers, at the Department of Social Medicine at Gothenburg University, warn that the phenomenon could develop into a public health issue and cause significant costs to society.
The interviews in the study were mostly conducted before the pharmacy reform which broke the state monopoly and allowed for regular retail stores to stock non-prescription.
"We don't know what effect increase access can have, but one suspects that over-use increases," Jonsson told the newspaper.
Jonsson explained that the most commonly suggested treatment for the condition is to scale down the use of painkillers which in turn prompts a short-term side effect of increased headaches and pain. (The Local)