Opioids are incredibly valuable for their ability to treat pain. Unlike some other side effects, constipation can stay with you for as long as you take an opioid. Opioids, when you’ve been using them to manage chronic pain, can cause constipation because their pain-relieving powers prevent your digestive tract (mainly your intestines) from working properly.1
You have opioid receptors throughout your entire body and when the opioid interacts with these in your brain it stops the feeling of pain. That’s the good bit.1
But when the opioid interacts with these receptors in muscles around your intestines, it can stop them from moving properly. Usually, the muscles around your intestines squeeze your broken-down food, which eventually becomes poo as it goes down further through a process called “peristalsis”. When opioids bind to receptors in the intestines, peristalsis doesn’t work as well. This means that your intestines can’t properly squeeze everything along like they normally would. Opioids can cause your sphincters (small rings of muscle, like your anus) to clench and become much smaller, slowing, or stopping your stool from moving through and eventually out. And that’s the bad bit.1
