What Is an Opioid Antagonist?

Your body has an opioid system made up of receptors that interact with naturally made opioid compounds (endogenous opioids). Opioids activate the receptors, which then influence your mood and the ways you process pain. Opioid antagonists reverse the effects of opioids by blocking the opioid receptors. This guide will explain how opioid antagonists work and their use in medicine.

Opioid Agonists, Partial Agonists and Antagonists: An Overview

Opioids and related drugs can fall into one of four categories based on their interaction with opioid receptors:

• Full agonists: An opioid agonist binds to opioid receptors and activates their functions. Agonists can attach to opioid receptors to varying extents. Full agonists tightly attach to opioid receptors, producing some of the strongest effects out of all opioid drugs. Opioids such as fentanyl, heroin, morphine and oxycodone count as full agonists.
• Partial agonists: Partial agonists activate opioid receptors to a lesser extent than full agonists. While partial agonists can have similar effects to full agonists, they lose effectiveness at higher doses. Opioids that belong to the partial agonist category include buprenorphine and tramadol.
• Antagonists: Opioid antagonists bind to opioid receptors to block the effects of opioids. Unlike opioid agonists, they do not produce a euphoric effect or alleviate pain. However, since they still bind to the receptors, they block the space opioids would normally go.
• Mixed agonists/antagonists: The opioid system includes multiple types of receptors that react to opioids differently. A mixed agonist/antagonist activity depends on the receptor type. It may act as an agonist for one type of receptor while working as an antagonist for another type of receptor.

Since the opioid system manages important functions like pain and mood, these compounds affect how your body works.

How Do Opioid Antagonists Interact With the Brain?

An opioid antagonist takes effect on someone who has opioids in their system. People who receive an antagonist without having already taken opioids will experience little to no effects.

However, when someone with opioids in their system takes an antagonist, the antagonist negates most of the opioids’ effects. In some cases, an opioid antagonist can trigger withdrawal symptoms because it blocks the receptors’ access to opioids.

About Opioid Antagonist Medications

The two most common opioid antagonist medications include:

• Naloxone: You can find naloxone in Suboxone®, a medication used to treat opioid addiction as a measure to discourage misuse. Naloxone is also used as a rescue medicine for opioid overdose and is commonly known by the brand name Narcan.
• Naltrexone: Some people in opioid addiction treatment take naltrexone to block the effects of opioids. As a result, they don’t feel the effects of opioids if they relapse.

These medicines help many people with opioid addiction manage their symptoms or recover from an overdose. Medical professionals and non-medical professionals can use naloxone to save the life of someone experiencing an opioid overdose.

Learn More About Opioid Agonists and Antagonists From Health Care Resource Centers

For more information about topics related to opioid addiction, visit our blog page. You can also contact our team online to schedule an appointment at one of our clinics in New England.

Medically Reviewed By:

Health Care Resource Centers Clinical Team

Health Care Resource Centers Clinical Team

The Clinical Team at Health Care Resource Centers is our team of physicians and medical directors within the organization. HCRC is a CARF accredited organization and has been providing addiction treatment services for over 32 years in the New England area.