Why Does Fentanyl Cause Itching?

Before answering the specific question of why does fentanyl cause itching, we’ll look at a brief overview of what opioids are in general. Opioids are used in pain management, but they can have intense side effects, ranging from addiction to respiratory failure and death. The itchiness associated with opioids may seem annoying, but it’s actually one of the least harmful side effects of using these drugs. There are illicit opioids sold only on black markets, such as heroin, but many opioids are prescription drugs that are administered in medical settings. Fentanyl is one of the most powerful prescription opioids, and it’s also unfortunately highly misused in the U.S. It’s intended for the treatment of breakthrough pain in cancer patients who are already receiving around-the-clock opioid-based pain management treatment, but it’s both misunderstood by doctors prescribing it, and by the people who use it all too often.

Fentanyl and itching isn’t the only side effect of this drug. This opioid analgesic includes a range of other potential side effects, such as:

• Nausea
• Vomiting
• Drowsiness
• Vertigo
• Dizziness
• Constipation
• Sweating
• Fatigue
• Palpitations
• Abdominal pain
• Dry mouth
• Malaise
• Weakness
• Swelling of arms and legs
• Muscle spasms
• Depression
• Rash

Along with the above symptoms, of course, itching is also a symptom of fentanyl. So, as well as the plethora of other potential symptoms, why does fentanyl cause itching?

Itching isn’t just a side effect of fentanyl. It’s also something that occurs with many other painkillers. The itching can be a mild annoyance, while in other situations it can lead patients to have to stop using painkillers, have lower doses, or use a different kind of painkiller. Until pretty recently doctors and researchers believed opioid-related itching was because of how the drugs interact with the user’s nervous system. There are brain receptors that respond to opioids, and most opioid painkillers are nonspecific. Nonspecific opioids bind to all of these receptors, which is why they’re so effective in dealing with pain. In research recently published by UNC School of Medicine in the Nature Chemical Biology Journal, it was shown that a specific receptor protein, MRGRPX2, can lead to an immune system response that then creates the itching that comes along with the use of opioids like fentanyl. Kate Lansu, who co-authored the paper, said that receptors in mast cells, which are part of the immune system, respond to an activation signal when opioids are taken. This response leads to the release of histamine and other inflammatory agents. The process has a specific name—degranulation. Lansu said that when this occurs, other cells go to the site of inflammation to clear what they sense as an infection, and it’s similar to what happens when someone has an allergic response. The hope is that by studying the specifics of why does fentanyl cause itching as well as looking at why other commonly used opioids cause itching, researchers will be able to develop an antagonist for this particular receptor, which would ultimately relieve the side effect of itching. So, to answer the question of why does fentanyl cause itching: it’s ultimately because when the opioid drug binds to certain receptors in your brain and body, it triggers a response not unlike an allergic response. Your body thinks it’s clearing an infection, thus the itching side effect.