Painkillers in the opium family may actually make pain last longer. Morphine treatment after a nerve injury doubled the duration of pain in rats, according to new research. The results raise the troubling prospect that in addition to having unpleasant side effects and addictive potential, opioids such as OxyContin and Vicodin could actually extend some types of pain. If a similar effect is found in people, suggesting that the treatment is actually contributing to the problem. Scientists have known that opioid-based drugs can cause heightened sensitivity to pain for some people, a condition called opioid-induced hyperalgesia. The new study shows that the effects linger weeks after use of the drugs is stopped. Male rats underwent surgery in which their sciatic nerves, which run down the hind legs, were squeezed with a stitch — a constriction that causes pain afterward. Ten days after surgery, rats received a five-day course of either morphine or saline. Rats that didn’t receive morphine took about four weeks to start recovering, showing less sensitivity to a poke. Rats that got morphine took about eight weeks to show improvements — double the time. These experiments were done with male rats, but unpublished data indicate that morphine extends pain even longer in female rats, results that fit with what’s known about differences in how males and females experience pain. https://www.sciencenews.org/article/morphine-may-make-pain-last-longer
