Codeine increases pain sensitivity

And the people with the worst side effects are those with chronic headaches.

“In the long-term it has the effect of worsening the problem rather than making it better,” said PhD student Jacinta Johnson, whose research compares codeine with morphine.

Codeine provides much less pain relief than morphine but causes the same level of increased sensitivity to pain, she said.

Professor Paul Rolan, a headache specialist at the Royal Adelaide Hospital, said