Opioids – or opiates – are a class of medication called analgesics, which means their primary medical function is pain relief.
Specifically, the Centers for Disease Control (CDC) indicates that opiates are analgesics like heroin, morphine, and codeine that are derived from the naturally occurring plant, Papaver somniferum, whereas opioids are synthetic medications, made in a laboratory, such as oxycodone, hydrocodone, methadone, and fentanyl.
Both opiates and opioids are incredibly powerful pain-relievers that act on the endogenous opioid receptors in the human central nervous system, called the endogenous opioid system.
However, there’s a problem with opioids.
The endogenous opioid system also plays a role in how we experience pleasure. It’s a key component in the good feelings we have after we eat, after we have sex, and after we engage in almost any enjoyable activity.
Therefore, when we take exogenous opioids/opiates, one of the side-effects – in addition to pain relief, which the medical reason for taking analgesics – is pleasure and/or general feelings of euphoria. That’s one reason opioids/opiates are so addictive: they leverage the most powerful internal pain relief system we have – the endogenous opioid system – by occupying the same receptors and triggering an even more powerful pleasure response than any endogenous opiates our body creates.
The Side Effects of Opioids
This article will discuss one of the most well-known side effects of opioids aside from pain relief and feeling of euphoria: the opioid itch.
We’ll explain what causes the opioid itch in a moment. First, we’ll share this list of the known side-effects of opioids/opiates, which we retrieved from the article “Opioids and Itching: What’s the Connection?”
Opioid/Opiate Side Effects
- Dry mouth
- Sexual dysfunction
- Fecal impaction
- Bowel obstruction
- Irregular breathing
These side effects may appear in various levels of severity, from mild and almost unnoticeable to extreme and life-threatening: in fact, irregular breathing and respiratory depression are the primary causes of opioid-related fatal overdose.
What about itching?
A study published in 2021 showed:
- 60%-90% of people who take lipophilic opioids – fentanyl, alfentanil, sufentanil, remifentanil – report itching
- Itching occurs within minutes and can last several hours
- 60%-85% of people who take intravenous morphine report itching
- Itching occurs within hours and can last for several days
That data is clear: itching, as a side-effect, is more common than not for people who take opioid medications.
But what causes the itch?
The Opioid Itch: Proposed Mechanisms
Research scientists propose three different mechanisms to explain the opioid itch. We’ll discuss each one now.
Mechanism One: Mast Cells
Mast cells are white blood cells that populate the connective tissue in the body, and are present in large quantities in the skin and nerves. White blood cells are immune cells. They respond directly to pathogens in the body, like bacteria or parasites, and help the body identify and eliminate these pathogens. But mast cells also contain chemicals called cytokines and histamine, which are involved in several types of immune response, including allergic reactions. When mast cells identify a pathogen, they may release histamine and cytokines, which aid in the immune response, but can also cause inflammation, and – the subject of our article – itching.
That’s how mast cells may contribute to the opioid itch, according to our latest scientific knowledge.
Mechanism Two: Direct Action of Opioids on Nerve Cells
Opioid receptors are present throughout the nervous system, including where the nervous system is directly adjacent to the skin. The nerve receptors in the skin, which are predominantly mechanoreceptors, may interact with opioids/opiates when they bind to nervous system opioid receptors adjacent to the skink, resulting in an uncomfortable itching sensation.
That’s how the action of opioids on nerve cells may contribute to the opioid itch, according to our latest scientific knowledge.
Mechanism Three: Injection Site Irritation
In some cases, people who use illegal opiates like heroin take them through injection directly into the bloodstream, known as intravenous (IV) injection. Injection can lead to infection, abscess, or injury at the injection site, which can cause uncomfortable itching. In addition, people who take IV heroin may pick at the injury, which exacerbates the injury and increases the itching sensation.
That’s how injection site irritation may contribute to the opioid itch, according to our latest scientific knowledge.
Opioid/Opiate Effects: Positive and Negative
We use opioids and opiates in medicine because they relieve pain so well: that’s a positive effect of opioids. While some may consider the euphoric properties of opioids a positive side-effect, that’s up for debate. It’s a good thing that people in extreme pain after an accident, injury, or major surgery may experience euphoria during recovery, that euphoria is also what causes people to engage in the recreational use of opioids.
In that way, we’d call euphoria a negative side-effect, because it increases the chance of developing opioid use disorder (OUD), which increases the chance of a fatal opioid overdose.
While itching, as a side-effect, is not nearly as serious as the potential dangers associated with the euphoric side-effect, it’s a serious problem for people who use opioids to control pain. The data shows that around 3/4ths of people given opioids for pain in a hospital setting experience itching.
The latest scientific knowledge includes proposed causes of the opioid itch. To date, however, the latest knowledge does not include a way to eliminate the opioid itch. We’ll keep any eye on the research and any developments. When scientists find a solution, we’ll share the news here immediately.