image showing a bunch of generic pills in a pill bottle - header image for opioid antagonist post on

Millions of people deal with chronic pain daily but are afraid to take opioids because of the addiction risk. Others are already addicted and are looking for a solution to their opioid problem.

If you’re one of these people, an opioid antagonist might change your life. Opioid antagonists can help you manage your condition with minimal side effects and opioid withdrawal symptoms.

In this article, we’ll cover everything you need to know about an opioid antagonist to help you decide if it’s right for you!

What Is an Opioid Antagonist?

Opioid antagonists are a special class of medicine that are prescribed for people who suffer from chronic pain, opioid use disorder, or an opioid overdose.

They work in your body’s central nervous system by blocking the effects of opioid (narcotic) drugs. This helps people who suffer from opioid use disorder (opioid addiction) by preventing the opioids from working.

How Do Opioid Antagonists Work?

When it comes to drugs and medicine, the word “antagonist” usually means a chemical that blocks or inhibits something.

In other words, opioid-antagonist medications work by going against opioids and blocking or inhibiting their action. More specifically, opioid antagonists block opioid receptors, which is why they’re often called opioid receptor antagonists.

But what happens when you block an opioid receptor? Well, normally, when an opioid or an opioid agonist (a drug that works like an opioid) binds to an opioid receptor, it triggers a series of reactions that cause relaxation and pain relief.

However, the degree of relaxation and pain relief depends on the type of opioid receptor. Generally speaking, there are three main classes of opioid receptors: delta, kappa (κ receptors), and mu receptors.

When mu receptors in your central nervous system are triggered, they cause the most respiratory depression (slowed breathing), analgesia (pain relief), and euphoria. This is why opioid pain medications are prescribed for chronic pain.

Unfortunately, the euphoric effect often leads to opioid abuse because people get hooked on the sensation. That’s why an opioid receptor antagonist is prescribed to block off the euphoric effect and treat opioid addiction.

Mu receptors are also found in areas of the peripheral nervous system, such as the lungs and the digestive tract. When you take opioids or opioid agonists, they can stimulate the peripheral opioid receptors in your intestines, slowing down their movement and causing constipation.

This is why opioid antagonists can help with opioid-induced constipation, which we’ll talk about later.

Examples of Opioid Antagonists

Some popular examples of opioid antagonists include:

  • Naltrexone
  • Naloxone
  • Nalmefene
  • Methylnaltrexone

Each has specific uses and different properties. Let’s take a closer look at each opioid antagonist.


The FDA first approved Naloxone as an “overdose reversal drug” in 1971. Since then, it’s saved millions of people on the verge of dying from an overdose.

Naloxone is also given to people suffering from respiratory depression due to opioids. It can restore breathing back to normal within 2-5 minutes, even if you’ve overdosed.

Traditionally, naloxone has been given as an injection, such as Narcan® and Zimhi®. However, the FDA has recently approved a nasal spray that contains naloxone, which is an excellent choice for people with needle phobia.

First responders, police officers, and EMTs usually carry naloxone in case they come across someone who’s overdosed on opioids.

You can also get naloxone over the counter if you have a family member or loved one who’s recovering from opioid addiction. It’s recommended to have it lying around in case they relapse at any time.


Naltrexone has been FDA-approved for substance abuse disorders, such as opioids and alcohol, since 1984. It’s extremely effective at blocking the euphoric effects of these substances, which makes it a cornerstone of addiction recovery.

However, unlike other opioid antagonists, naltrexone doesn’t help when managing withdrawal symptoms.

Naltrexone can be given as an injection, such as Vivitrol®, or an oral tablet such as Depade®.


Nalmefene is another FDA-approved opioid antagonist. However, Nalmefene is mainly used in case of an acute opioid overdose.

It has a mechanism of action that’s similar to naloxone, but it stays in your system longer. Unfortunately, that means it’s more likely to cause withdrawal symptoms. Nalmefene also causes withdrawal symptoms much faster than other opioid antagonists.

If you suffer from an opioid addiction, your doctor will likely give you naloxone as a first choice instead of nalmefene.

Nalmefene is mainly available in injection form under the brand name Revex®.


Methylnaltrexone is a modified form of naltrexone. It’s designed to target the peripheral opioid receptors in your body without affecting the central ones.

That’s why methylnaltrexone is mainly used for opioid-induced constipation. After administration, it reaches the receptors in your intestines and blocks them, so your digestion and intestinal movement aren’t affected.

At the same time, methylnaltrexone doesn’t affect your central nervous system, so you still get all the painkilling effects from opioids. Methylnaltrexone is usually given to people with severe chronic pain who take opioid analgesics.

The most popular brand name for Methylnaltrexone is Relistor®, which includes both injections and oral tablets.

Opioid Antagonist Uses

While opioid antagonists are famous for treating opioid use disorder and opioid addiction, they have several other medical benefits. Here are the different medical uses of opioid antagonists.

Opioid Use Disorder

Opioid use disorder is perhaps the most common and popular indication for opioid antagonists. They help you get over your addiction by blocking opioid receptors and hence prevent opioids from taking effect.

It doesn’t matter how much opioids you take. Blocked receptors mean there’s no euphoric effect, which is the main reason people get addicted to opioids in the first place.

Without this euphoric effect, your urge to take opioids gets smaller and smaller until you eventually build up the will to stop.

These opioid antagonists can result in unpleasant withdrawal symptoms as your body struggles with the lack of opioids. You might feel things like muscle aches, pain, sweats, anxiety, and other mental side effects.

Luckily, these side effects are worse at the beginning. As you delve into your recovery journey with opioid antagonists, they become less prominent, and eventually, you stop experiencing withdrawal symptoms altogether.

Acute Opioid Overdose

Opioid antagonists, such as Naloxone, are commonly used to reverse opioid overdose. They’re usually given as injections that travel the bloodstream looking for opioid receptors and quickly block them off.

Of course, the sooner you’re able to take an opioid antagonist after an overdose, the better your chances of survival. You might still experience some respiratory depression, but a shot of Naloxone, for example, might keep your lungs from ceasing.

Opioid-Induced Constipation

According to the American Cancer Society, more than 600,000 people die of cancer each year in the U.S., and the number keeps rising. During the end stage of cancer, most patients are prescribed opioids to help manage their pain.

Unfortunately, these opioids lead to constipation, which is why opioid antagonists are often prescribed alongside them.

Antagonists can help relieve the abdominal pain, vomiting, bloating, and other symptoms that accompany constipation.

Treating Respiratory Depression

One of the main side effects of opioids is respiratory depression. This is due in part to the mu receptors’ effect on the lungs, but there’s also another mechanism of action not many people know.

Studies in the JPSM (Journal of Pain and Symptom Management) show that opioids also reduce your body’s sensitivity to carbon dioxide. This means you might have high levels of carbon dioxide in your blood, and your lungs aren’t picking up on it.

Normally, when your lungs sense too much carbon dioxide, they kick your breathing up a notch. The idea is to expel the excess carbon dioxide and bring in more oxygen.

However, with opioids impairing your lungs’ sensitivity, your lungs start lowering your respiration level, which can be fatal if it goes on for too long.

That’s where opioid antagonists come in. They block the opioid receptors responsible for all of this, bringing your lungs’ sensitivity back to normal. Doctors might prescribe an opioid antagonist to prevent this respiratory depression or even treat it.

Treating Nausea and Vomiting

Nausea and vomiting are two common side effects of opioids, especially when you first start taking the drugs. This is because opioids can stimulate the vomit center of the brain (called the CTZ or chemoreceptor trigger zone).

The unpleasant feeling of being nauseous sometimes makes it hard to take your medication or stick to your treatment plan, let alone the vomiting. That’s why your healthcare provider might prescribe an antiemetic (anti-vomiting) drug to help minimize or prevent these symptoms.

Opioid antagonists, in particular, are famous for treating opioid-induced nausea and vomiting because of their ability to:

  • Block the CTZ: By blocking the opioid receptors in your brain’s vomiting center, opioid antagonists allow pain relief without the unpleasant nausea and vomiting.
  • Slow down digestion: Slowing down the movement of your digestive tract leads to slowed digestion and makes you less likely to vomit or feel nauseous.

Skin Itching or Pruritis

Although quite rare, hospitalized patients taking opioids can develop skin rashes and itchy skin, which is called pruritus. This is caused by the mu receptors in the skin and usually stops after a few days.

However, opioid antagonists can help reduce the itching that occurs with the first few doses of opioids.

Alcohol Dependence (Alcohol Use Disorder)

Opioid antagonists can also help people with alcohol dependence or alcohol use disorder.

When you drink too much alcohol, your body releases endogenous opioids, which cause a euphoria similar to that of opioid use. By blocking opioid receptors, opioid antagonists stop the feeling of euphoria when you drink alcohol.

If you no longer feel good, it makes it easier to quit or cut back on your drinking. However, opioid antagonists need to be combined with other abstinence medications for the most benefits. Your healthcare provider can determine which drug combination is best for you.

Side Effects of Opioid Antagonists

Most opioid antagonists don’t have side effects per se. The side effects you experience after taking them are usually withdrawal symptoms that happen because the opioids no longer work.

Here are a few examples of these withdrawal symptoms:

  • Dizziness and drowsiness: You might feel lightheaded and sleepy, especially when getting up from a lying position.
  • Headache: Having opioids and opioid antagonists in your bloodstream can lead to blood flow changes, causing a headache.
  • Fatigue: Feeling extremely tired and lacking energy.
  • Muscle weakness and pain: You might experience trouble lifting your arms or legs or feel weak overall.
  • Sweating and chills: Opioid withdrawal leads to hormonal changes that can cause excessive sweating and chills.
  • Restlessness and agitation: When you stop taking opioids, your body craves the euphoric effects, leading to anxiety, agitation, mood swings, and difficulty concentrating. This usually interferes with your daily activities and social interactions.
  • Hyperventilation: Your anxiety might lead to rapid shallow breathing, known as hyperventilation.
  • Runny nose and watery eyes: Opioid withdrawal causes a general increase in bodily secretions
  • Tachycardia: You might experience a fast heart rate, possibly from anxiety

The severity of these side effects depends on how addicted your body is to opioids. If you’ve taken a large amount of opioids or have been doing so for a long time, the withdrawal symptoms are usually worse.

Healthcare providers can help you navigate or minimize these side effects, especially if you’re at a hospital.


Opioid antagonists are a major asset in the fight against the opioid epidemic.

Whether it’s an opioid overdose, opioid addiction, or chronic pain, opioid antagonists can help you recover with as few side effects as possible.

Not only are they life-saving, but they can make your life much easier on your recovery journey.

Comments (0)

More Resources, to
help your Recovery

If you’re ready to take the first step on your road to recovery, we’re here for you. Please book an appointment with us today, and let’s get you back to where you want to be.
Certified, Proven and Private

Curednation: A Safe Space For Recovery

If you’re ready to take the first step on your road to recovery, we’re here for you. Please book an appointment with us today, and let’s get you back to where you want to be.