Little gain from long-term pain relief
Researchers have found that codeine may produce a heightened sensitivity to pain if used for extended periods of time.
University of Adelaide researchers compared the impact and effects of codeine and morphine on patients, and found that codeine provided less pain relief than morphine, but left patients with a similar level of pain sensitivity.
Lead author and PhD student Jacinta Johnson said pain sensitivity can be a major issue for users of opioid drugs because the more you take, the more the drug can increase your sensitivity to pain, resulting in patients never quite getting the relief required.
“In the long term, it has the effect of worsening the problem rather than making it better,” Ms Johnson said. “We think that this is a particular problem in headache patients, who seem more sensitive to this effect.
“Both codeine and morphine are opioids but codeine is a kind of ‘Trojan horse’ drug – 10 per cent 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.”
Professor Paul Rolan, a headache specialist at the University of Adelaide, said codeine has been widely used as a 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,” Professor Rolan said.
Professor Rolan said while more research was needed, the laboratory findings suggested a potential problem for anyone suffering from chronic pain who needed 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 headaches.
“This can be a very difficult issue for many people experiencing pain, and it creates difficulties for clinicians who are trying to find strategies to improve people’s pain.”
The research was presented at the 2013 International Headache Congress in the United States.