Opioids are a class of G-protein receptors found in many parts of the body and have a wide variety of roles. They are found in the highest density in our brains. When opioids 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.
Opioid receptors also cause suppression of our respiratory drive, which is why overuse of opioid medications can lead to overdose and even death. Opioid receptors are also found in other parts of the body other than the central nervous system. For example, activation of the opioid receptors in our gastrointestinal tract slows down the motility of our gut. This is why opioid use can cause constipation.
The medical community is continuing to learn about the many roles that opioid receptors play in our bodies.