Why painkillers sometimes make the pain worse
Mark Hutchinson could read the anguish on the participants’ faces in seconds. As a graduate student at the University of Adelaide in Australia in the late 1990s, he helped with studies in which people taking methadone to treat opioid addiction tested their pain tolerance by dunking a forearm in ice water. Healthy controls typically managed to stand the cold for roughly a minute. Hutchinson himself, “the young, cocky, Aussie bloke chucking my arm in the water,” lasted more than 2 minutes. But the methadone patients averaged only about 15 seconds.
“These aren’t wimps. These people are injecting all sorts of crazy crap into their arms. … But they were finding this excruciating,” Hutchinson says. “It just fascinated me.” The participants were taking enormous doses of narcotics. How could they experience such exaggerated pain?
The experiment was Hutchinson’s first encounter with a perplexing phenomenon called opioid-induced hyperalgesia (OIH). At high doses, opioid painkillers actually seem to amplify pain by changing signaling in the central nervous system, making the body generally more sensitive to painful stimuli. “Just imagine if all the diabetic medications, instead of decreasing blood sugar, increased blood sugar,” says Jianren Mao, a physician and pain researcher at Massachusetts General Hospital in Boston who has studied hyperalgesia in rodents and people for more than 20 years.
Read more http://www.sciencemag.org/news/2016/11/why-painkillers-sometimes-make-pain-worse
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