As if migraines were not bad enough, a US study has found that sufferers are also more prone to splitting head pain after drinking too much.

Researchers from the Jefferson Headache Centre repeatedly stimulated headaches in rats' brains by injecting the outer membrane of the brain with an inflammatory mixture.

One group of rats were given oral doses of alcohol, the equivalent of one to two shots of liquor, after the induced headache. Another group, whose brains were not injected with the inflammatory mixture, were also given similar oral doses.

The study found that the rats which were injected with the headache-inducing mixture and then given alcohol initially felt little pain.

But four to six hours later, their pain sensitivity increased compared to the other group.

"Our results suggest that dehydration or impurities in alcohol are not responsible for hangover headache," said Michael Oshinsky, assistant professor of neurology at Thomas Jefferson University and a member of the Jefferson Headache Centre team.