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What Are Opioid Receptors?

Elena Hill, MD, MPH profile image
Medically Reviewed By Elena Hill, MD, MPH • Updated Aug 2, 2023

Opioid receptors are found on cells in the highest density in our brains, but they are also in other parts of the body.

When opioids (such as Vicodin, OxyContin, or heroin) bind to the opioid receptors, this sets off a chemical reaction in the body that produces euphoric effects and also plays a role in pain control and pleasure.

The medical community is continuing to learn about the many roles that opioid receptors play in our bodies. 

How Many Opioid Receptors Are There?

Scientists have discovered many types of opioid receptors. As of now, there are five main categories of opioid receptors that you might see:[1]

  1. Mu receptor: Opioid attachment to these receptors produces a variety of changes, including pain control, drug dependence, euphoria, respiratory depression, and constipation.
  2. Kappa receptor: Opioid attachment to these receptors produces pain control and a feeling of floating or disassociation.
  3. Delta receptor: Opioids attaching here produce pain control and constipation. 
  4. Nociceptive receptor: Opioids attaching here produce pain control. 
  5. Zeta receptor: Opioids attaching here can help to regulate tissue and cell development.

This is of course a simplification – there are likely many different types of opioid receptors, and scientists are just beginning to understand the differences in how each of these receptors impacts us. 

What Changes Do Opioid Receptors Produce?

Opioid receptors, when stimulated, have multiple effects in the body, including:


At even low to moderate doses, opioids can produce euphoria or a feeling of being “high”. 

Pain Control

Multiple opioid receptors can change pain responses and deliver relief.[2] This is the main pharmacologic use of opioids – as painkillers. 

Immune System Suppression

Your immune system should be on and working every moment. But studies suggest that opioids can alter the action of this critical system.[3] 


Opioid receptors found in the digestive tract causing a slowing of digestion, which can often lead to constipation. 


Opioids stimulate physical dependence over time, so that individuals who take them regularly develop withdrawal symptoms when opioid are discontinued abruptly. [4]

Respiratory Suppression

Opioid receptors also cause suppression of our respiratory drive, which is why overuse of opioid medications can lead to overdose and even death.


  1. Physiology, Opioid Receptor. StatPearls. July 2021. Accessed July 2022.
  2. Opioid Receptors in Immune and Glial Cells: Implications for Pain Control. Frontiers in Immunology. March 2020. Accessed July 2022.
  3. The Role of Opioid Receptors in Immune System Function. Frontiers in Immunology. December 2019. Accessed July 2022.
  4. 4. Opioid Receptors: Drivers to Addiction? Nature Reviews Neuroscience. June 2018. Accessed July 2022.

Medically Reviewed By Elena Hill, MD, MPH

Elena Hill, MD; MPH received her MD and Masters of Public Health degrees at Tufts Medical School and completed her family medicine residency at Boston Medical Center. She is currently an attending physician at Bronxcare Health Systems in the Bronx, NY where ... Read More

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