Patients suffering from chronic pain may rely on painkillers to cope with their illness, and possible addiction and abuse is always a concern. However, researchers have found a new problem with opioid painkillers, with one study suggesting these drugs can actually increase pain when used long-term.
Professors Peter Grace and Linda Watkins, along with colleagues at the University of Colorado at Boulder, published their study in the Proceedings of the National Academy of Sciences May 30th. Although the short-term effects of morphine are well-known, the researchers wanted to know the long-term effects of morphine use, so they enlisted rats to help them find out.
The researchers split rats suffering from chronic nerve pain into two different groups. While one group remained as a control, the researchers treated the other rats with morphine. Long-term morphine use can lead to addiction, but the researchers treated the rats for only five days, which should not be long enough for them to become dependent. Even in that short time, the researchers discovered that the treatment seemed to be worsening pain for the rats. Not only that, the rats treated with morphine experienced chronic pain even months after the treatment, while the untreated rats experienced less long-term pain. This suggests that although morphine can help rats cope with their pain at first, the effects not only wear off quickly but the opioids also cause an increase in pain and persistent problems.
According to the researchers, when the rats receive a peripheral nerve injury, a message travels from the nerve cells to immune cells in the spinal cord, called glial cells. Normally these cells remove microorganisms and other debris, but when they receive a pain signal, these glial cells become ready for action. When the researchers treated the injury with morphine, however, it caused the glial cells to overreact, causing spinal cord inflammation among other things. The glial cell reaction causes a protein called interleukin-1 beta (IL-1b) to signal pain-responsive nerve cells in the spinal cord and brain. This increases feelings of pain that can then last several months.
Although the research involved rats, the same actions likely happen in humans as well. This means that although treating someone with morphine after an initial injury may help lessen their pain, doctors should consider limiting morphine use to a short time to avoid an increase in pain and chronic pain. This adds to the possible dangers of morphine and opioid drug use, with the chance of opioid addiction.
According to the National Institute on Drug Abuse, in 2015 alone, 20,000 people in the U.S. died from prescription opioid pain reliever overdose. Sometimes someone treated with morphine will continue seeking out the drug after becoming addicted, and sometimes someone will start taking the drug on their own with the intention of getting high. Either way, the person taking the opioids faces dangers ranging from chronic pain to death.
Although the research alerts doctors to another danger of opioid use, the researchers did make a positive finding. The scientists discovered ways to block certain glial cell receptors that recognize opioids. Using a designer drug technology called Designer Receptors Exclusively Activated by Designer Drugs (DREADD), the researchers were able to turn off certain glial cells. This discovery could help relieve pain without triggering chronic pain.
About 100 million people in the U.S. suffer from chronic pain, which is defined as
pain lasting for more than twelve weeks, although the causes vary including injury or illness. Besides various medications, some patients may find relief from chronic pain through surgery, nerve blocks or electrical stimulation, alternative therapies like acupuncture, or self-management to cope with their daily tasks despite the pain. Although opioid drugs can help at first, current research suggests that use of painkillers may actually be exasperating the chronic pain people are trying to manage. Once those who have become dependent on opioids stop taking the drugs, they can face withdrawal symptoms like restlessness, involuntary leg movements, insomnia, cold flashes and goosebumps, nausea and diarrhea, and muscle and bone pain.