ringfield, Mo.) -- If you've ever had a migraine, you know it can be a pain in the neck... and the head... and the face. Even worse, it can be difficult to get rid of.

Rhonda Cadle has suffered debilitating migraines for decades.

"It actually feels like a hammer pounding from the inside out," says Cadle.

She also has a hard time treating them. She says some medicines even increase her pain.

"They weren't working and I'm like, 'they work for everyone else, what's wrong with me?'" says Cadle.

It's a question Dr. Roger Cady has heard before. Now he may have an explaination.

"There is probably a biological reason for non-response," says Cady.

The Headache Care Center, with Missouri State University, found people with low levels of the Calcitonin Gene-Related Peptide (CGRP) in their spit didn't respond to rizatriptan, a common migraine medication.

"If there wasn't CGRP in the saliva, in any part of the migraine that we measured, that population of people did not respond," says Cady.

CGRP works as a messenger between nerves, kind of like an email. Unfortunately, the message it relays is pain. So, those with high levels of CGRP are experiencing more pain, or a worse migraine.

Researchers found some will feel that pain, without high levels of CGRP, and that could change the way migraines are diagnosed.

"Even though people share the same symptoms it doesn't necessarily mean that they're all having the same process going on in their nervous system generating those symptoms," says Cady.

This study is considered 'investigator initiated.' More studies need to be done, but researchers say the data was statistically singificant.

"Potentially, this could allow people to select the right medicine for the right headache," says Cady.

You can check out the findings in the October issue of the Headache Journal. It comes out later this month.

Contact: dmagditch@kspr.com