Opioid Receptors: Definition, Types, Functions, and Examples (2024)

Opioids slot into opioid receptors and activate them. This sends signals to your brain to relieve pain and promote pleasure.

Both endogenous opioids, which your body naturally produces, and exogenous opioids, which are opioid medications or substances, can activate opioid receptors.

The receptors are part of your body’s endogenous opioid system, which deals with pain, reward, and addiction. They’re present on nerve cells, mainly in your central nervous system (CNS) and gut.

There are three main types of opioid receptors: mu, delta, and kappa. Although they’re similar in some ways, they’re distributed differently throughout your body and can produce different effects.

Mu opioid receptors occur throughout your CNS, particularly in areas that deal with sensory perception.

These were the first opioid receptors to be discovered. Those who found them named them after their sensitivity to morphine.

Later on, however, experts found that most opioid drugs could activate mu receptors, and that this could lead to dependence on these drugs in some cases. Side effects like breathing difficulties and constipation can also happen.

However, these are also the main receptors for the body’s own opioids, sending chemical signals that reduce certain brain neuron activity. This leads to pain relief and the stimulation of the reward system, which can result in dopamine production and feelings of euphoria.

There are fewer delta opioid receptors throughout your body. They tend to accumulate in the forebrain.

When they bind with some of the body’s own opioids, called enkephalins, they can reduce anxiety as well as pain. This suggests that the receptors play a role in mood regulation.

One study found that targeting delta opioid receptors could reduce pain for longer and may result in fewer side effects when treating pain.

Delta receptors may have other roles, too, involving cardiovascular regulation and the movement of food through the gastrointestinal system. However, these roles need further research.

Kappa opioid receptors bind with natural opioids in the body called dynorphins.

They’re the only opioid receptor that doesn’t cause respiratory depression. They can also have an anti-reward, dysphoric effect, which is the opposite effect of mu receptors.

So, while they do provide pain relief like the other opioid receptors, their side effects are generally less severe. You’re also less likely to become dependent on a drug that binds with a kappa receptor.

This all means that they may be a good candidate for newer forms of pain treatment. Research is ongoing in this area.

However, one review notes that withdrawal from opioids can cause stress in the body, boosting the function of kappa receptors and potentially making relapse more likely due to a continued dysphoric mood.

Opioid drugs, which doctors typically prescribe for pain relief, can activate opioid receptors just like the body’s natural opioids can. But there’s research to suggest that they work in a slightly different way to endogenous opioids.

While naturally produced opioids activate receptors on the surface and inside of nerve cells, opioid drugs may also activate extra parts of nerve cells. And it’s this additional activation that may lead to problematic side effects.

With long-term use, opioid drugs like oxycodone and morphine can also lead to addiction due to the euphoria that people feel when taking them.

Opioid addiction is fueled by the opioid receptors turning off certain nerve cells in the midbrain, allowing dopamine to take over.

Dopamine makes the opioid drug feel rewarding, leading people to want to take more. When a person no longer takes these drugs, the body switches the other way, causing feelings of dysphoria and anxiety and leading to more opioid cravings.

Three primary types of opioid receptors — mu, delta, and kappa — exist in the body.

Opioids that the body naturally produces and opioids that you take in the form of a medication or substance can activate these receptors.

All opioid receptors have a positive effect on pain. But some come with unwanted side effects, including addiction, particularly if the receptors are activated over and over again in the long term.

Lauren Sharkey is a United Kingdom-based journalist and author specializing in women’s issues. When she isn’t trying to discover a way to banish migraine, she can be found uncovering the answers to your lurking health questions. She has also written a book profiling young female activists across the globe and is currently building a community of such resisters. Catch her on Twitter.

Opioid Receptors: Definition, Types, Functions, and Examples (2024)


What are the 5 types of opiate receptors? ›

Kappa opioid receptor (KOR) is one of the four receptors in the opioid receptor system. The other three are mu (MOR), delta (DOR), and nociceptin (NOR) opioid receptors. They are also called κ, μ, δ, and nociceptin (or nociceptin/orphanin FQ) peptide receptors (KOP, MOP, DOP, and NOP, respectively).

What are opioid receptors' functions? ›

Opioid Receptors are G protein-coupled receptors (GPCRs). They mediate the human body's response to most hormones, neurotransmitters, drugs, and are involved in sensory perception of vision, taste, and olfaction. [2] All GPCRs consists of seven transmembrane spanning proteins that couple to intracellular G proteins.

What are my opioid receptors? ›

Opioid receptors are found throughout your central and peripheral nervous systems, as well as in your gastrointestinal (GI) tract. These receptors regulate many body functions, including: Pain. Mood.

What is the function of the opioids? ›

How do opioids work? Opioids attach to proteins called opioid receptors on nerve cells in the brain, spinal cord, gut, and other parts of the body. When this happens, the opioids block pain messages sent from the body through the spinal cord to the brain.

What is the most common opioid receptor? ›

MORs are present in the central nervous system (CNS) and are the most commonly expressed opioid receptors. These receptors are expressed in the dorsal horn of the spinal cord and different brain regions (primarily the somatosensorial cerebral cortex) that are involved in processing nociceptive (pain) signals.

What are the four main receptor types? ›

Types of Receptors:
  • Nuclear receptors.
  • Enzyme-linked receptors.
  • G-protein coupled receptors.
  • Ligand-gated ion channels.

What drugs work on opioid receptors? ›

Treating opioid addiction

Researchers have developed medications to help people recover from opioid addiction. Methadone and buprenorphine (Suboxone, Subutex) both activate the opioid receptors just enough to prevent an opioid-addicted person from feeling withdrawal or cravings, but not enough for them to get high.

What is the role of opioid receptors in the immune system function? ›

Opioids modulate both branches of the immune system by binding to the μ receptor (also known as the MOP receptor), which ultimately leads to an impaired ability of the host organism to clear pathogens (Figure 1) (Abbas et al., 2014).

What receptor does oxycodone bind to? ›

Upon oral administration, oxycodone binds to opioid receptors, thereby mimicking the effects of endogenous opiates to provide analgesia.

What are the families of opioid receptors? ›

Three major categories of opioid receptors have been identified and cloned: mu-opioid receptor (MOR), kappa-opioid receptor (KOR), and delta-opioid receptor (DOR), with differences in affinity and selectivity to endogenous peptides.

Where are opioid receptors localized? ›

Opioid receptors are distributed at various sites from nerve endings in the skin, to the cerebral cortex and various nuclei located along nociceptive pathways, such as the dorsal raphe or the lateral parabrachial nucleus.

What is the delta opioid receptor? ›

The δ-opioid receptor, also known as delta opioid receptor or simply delta receptor, abbreviated DOR or DOP, is an inhibitory 7-transmembrane G-protein coupled receptor coupled to the G protein Gi/G0 and has enkephalins as its endogenous ligands.

What is the function of each opioid receptor? ›

Mu receptors influence responses to mechanical, chemical, and thermal nociception at a supraspinal level. Kappa receptors appear to modulate spinally mediated thermal nociception and chemical visceral pain. Delta receptors may modulate mechanical nociception and inflammatory pain.

What pain killer is the strongest? ›

Carfentanil: Carfentanil, a synthetic opioid, is a 100-fold stronger version of fentanyl. It has 5,000 times the potency of heroin and 10,000 times the potency of morphine. There has been an increase in the amount of carfentanil in narcotics, and this substance nearly invariably results in overdose and death.

How do opioids function in the body? ›

Opioids bind to and activate opioid receptors on cells located in the brain, spinal cord, and other organs in the body, especially those involved in feelings of pain and pleasure, and can strongly reinforce the act of taking the drug, making the user want to repeat the experience.

What are the 5 A's of opioid response? ›

For this reason, we recommend Five A's of assessment: Analgesia, Activity, Adverse reactions, Aberrant behavior and Affect. Every person for whom opioids are prescribed has the potential to abuse their medication (Webster & Dove, 2007).

What are the three opioid receptor subtypes? ›

Mu (μ), kappa (κ), and delta (δ) opioid receptors represent the originally classified receptor subtypes, with opioid receptor like-1 (ORL1) being the least characterized.

How many opioid receptors are in the brain? ›

Opiate Receptor Classes

Early work by Martin and associates led to the postulation of three opiate receptors: mu, kappa, and sigma. Later studies by Kosterlitz and colleagues led to the identification of the delta opioid receptor.

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