Morphine may worsen chronic nerve pain
Taking morphine for chronic nerve pain (neuropathic pain) may actually worsen the problem rather than help it, new evidence suggests.
It shows that morphine can more than double the duration of pain, as well as amplifying its severity.
The results, published in the journal Proceedings of the National Academy of Sciences (PNAS), come at a time when opioid use for pain management is at an all time high.
The findings further call into question the use of opioid-based painkillers and treatments such as morphine, oxycodone and methadone, say the researchers.
However, they say there may be a way to switch off this pain-amplifying mechanism.
Studies led by and conducted at the University of Colorado Boulder in the United States found that rats with chronic nerve pain treated with morphine for just 5 days experienced prolonged pain sensitivity. This lasted for up to 2-3 months – more than double that experienced in the control group.
"What we found is that the opioid painkiller activates spinal immune cells, causing a further inflammatory response. The pain is effectively transitioned to a chronic state, making the pain itself both more severe and longer lasting," says study author Dr Peter Grace, Research Assistant Professor with the University of Colorado Boulder, and Research Associate in Pharmacology at the University of Adelaide's School of Medicine.
"This extended period of chronic pain has followed from just 5 days of treatment with morphine, which in itself is very significant," he says.
Dr Grace says the results are of concern because of the huge number of opioid prescriptions being written for patients each year. "Our results add weight to the growing body of science suggesting that treatment with opioids such as morphine may in fact be a contributor to people's chronic pain," he says.
However, he says novel drugs are currently in the pipeline that prevent the immune response from kicking in, enabling the painkilling benefits of morphine to be delivered without resulting in further chronic pain.