Asian Scientist (Sep. 13, 2013) – Using large and frequent doses of the pain-killer codeine may actually produce heightened sensitivity to pain, without the same level of relief offered by morphine, according to researchers in Australia.
The researchers conducted what is believed to be the world’s first experimental study comparing the pain relieving and pain worsening effects of both codeine and morphine.
Professor Paul Rolan, who is a headache specialist, says codeine has been widely used as pain relief for more than 100 years but its effectiveness has not been tested in this way before.
“In the clinical setting, patients have complained that their headaches became worse after using regular codeine, not better,” said Rolan.
“Codeine use is not controlled in the same way as morphine, and as it is the most widely used strong pain reliever medication in the world, we thought it was about time we looked into how effective it really is.”
In laboratory studies, PhD student Jacinta Johnson found that codeine provided much less pain relief than morphine, but resulted in the same level of increased sensitivity to pain.
“Pain sensitivity is a major issue for users of opioid drugs because the more you take, the more the drug can increase your sensitivity to pain, so you may never quite get the level of relief you need,” said Johnson, who presented this research at the 2013 International Headache Congress in Boston.
According to her, this has the effect of worsening the problem in the long term, especially in headache patients as they seem to be more sensitive to this effect.
“Both codeine and morphine are opioids but codeine is a kind of ‘Trojan horse’ drug – 10% of it is converted to morphine, which is how it helps to provide pain relief. However, despite not offering the same level of pain relief, we found that codeine increased pain sensitivity just as much as morphine.”
Rolan says while more research is needed, these laboratory findings suggest a potential problem for anyone suffering from chronic pain who needs ongoing medication.
“People who take codeine every now and then should have nothing to worry about, but heavy and ongoing codeine use could be detrimental for those patients who have chronic pain and headache,” said Rolan.
Rolan is now running a clinical trial testing a new approach to treating codeine-related headache.
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Source: University of Adelaide; Photo: Sarah G../Flickr/CC.
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