Opiate-blocking drugs, or opioid antagonists, stop narcotics from binding to the opioid receptors in the brain.

Naltrexone and naloxone are the most familiar opioid blockers.

What are Opiate-Blocking Drugs?

Opioid blockers, or opioid antagonists, stop opioid substances from attaching to the delta, kappa, or mu receptors on neurons in the brain. Opioid antagonists bind to these receptors on neurons, and they sometimes kick opioids off those receptors and replace them. This prevents the action of the opioid drug for the length of time it takes for the opioid antagonist to be metabolized through the body.

Because opioid blockers attach to the opioid receptors that are on neurons, there have been some reported analgesic effects, leading to reduced pain sensations. There is little or no breath depression, heartbeat irregularity, or changes to digestion — all issues that are present for narcotic painkillers.

While there are several drugs considered opioid blockers, only two are given as prescription substances in the United States: naloxone and naltrexone. Both of these medications block exogenously administered opioids or narcotic substances that are not directly produced by the brain, like morphine, heroin, oxycodone, hydrocodone, meperidine, codeine, and methadone. These medications may also block endogenously released endorphins or enkephalins, like the brain’s natural opioids.

How Do Some Drugs Block Opioids From Neuron Receptors?

There are three basic types of chemicals that affect the opioid receptors in the brain.

Agonists

These are opioid drugs like codeine, methadone, or fentanyl that bind to the opioid receptors found on neurons. They activate these receptors to produce analgesia, relaxation, tiredness and suppressed breathing. While feelings of euphoria, intoxication, and pain relief may not last more than a few minutes or hours, many of the other effects can continue for much of the day.

Partial Agonists

The most famous and important partial agonist is buprenorphine, which binds to opioid receptors in the brain to relieve pain. In people who have struggled with high-dose opioid abuse, buprenorphine relieves withdrawal symptoms like anxiety and cravings. These drugs do not produce any feeling of intoxication unless the person is opioid-naïve.

Antagonists

While these drugs bind to opioid receptors and may paradoxically produce some analgesia, antagonists are mainly used to stop opioids from binding to these receptor sites on neurons or to kick them off if they are present.

Antagonists force the body to react differently to agonists and partial agonists, which can be very helpful when treating opioid addiction or overdose. There are about a dozen chemicals considered opioid antagonists, including:

  • Those that relieve moderate to severe pain, such as pentazocine, nalbuphine, buprenorphine, butorphanol, and dezocine.
  • Those that treat opioid-induced constipation or bowel issues, such as methylnaltrexone, naloxegol, eluxadoline, and naldemedine.
  • Those that reverse overdose effects, such as naloxone, levallorphan, nalorphine, and diprenorphine (specifically works for carfentanil, a potent fentanyl analog).
  • Those that block opioids from binding to neurons, such as naltrexone and nalmefene.

While some medical studies are examining the use of low doses of opioid antagonists to treat pain, there are two drugs used in opioid addiction treatment in the U.S. Few others are used at all.

Naloxone And Naltrexone: The Main Opioid Blockers

Naloxone and naltrexone are the most famous opioid antagonists in the U.S. and the most widely used.

Naloxone

This drug is notorious for “reversing” opioid overdoses. While this effect does not last forever since naloxone has a shorter half-life than most opioid drugs, the substance does push opioids off the brain’s opioid receptors, which can block the toxic effects of an opiate overdose long enough for medical help to arrive.

While naloxone has been available to emergency medical personnel and hospitals for several years, the U.S. Food and Drug Administration (FDA) approved the nasal spray for more general use in 2015.

Naloxone can be administered either as an intranasal spray, an intramuscular injection, a subcutaneous (under the skin) injection, or intravenous injection. Some people use the auto-injector Evzio to administer the opioid blocker to people who have overdosed on opioids. It is said that Evzio is easy to use and provides instructions on what to do after an opioid overdose occurs. Many states are expanding access to naloxone through pharmacies. Instead of requiring someone to have an opiate prescription or be a caregiver to someone who takes opiates to manage pain, Good Samaritan laws have allowed expanded naloxone access.

Anyone who sees someone experiencing an opiate overdose can administer the drug. This is typically in the form of the nasal spray since it is the easiest to administer.

This chemical has also been added to buprenorphine as one approach to managing withdrawal symptoms during opioid detox. Suboxone is the brand name for the medication that combines these two drugs. Buprenorphine, as a partial opioid agonist, eases physical and psychological discomfort associated with opioid withdrawal by binding to the opioid receptors in the brain without causing euphoria.

The naloxone in Suboxone does not take effect unless the person tries to abuse the substance by destroying the time-release aspects of the medication. At that point, naloxone is released instead and stops buprenorphine or any other opioids from binding to the brain and causing a high. This sends the individual into withdrawal, and they will likely require further medical treatment.

People who may benefit from naloxone treatment during detox include those who:

  • Receive rotating opioid medication regimens, as directed by their doctor. These drugs may overlap accidentally necessitating naloxone intervention.
  • Have been discharged from emergency opioid overdose treatment.
  • Are completing mandatory opioid detox or abstinence programs.

Unlike many medications, there are no known problems with naloxone like dependence or tolerance. It is possible to have an allergic reaction to the drug, which would cause symptoms like swelling in the face, lips, or throat. This reaction requires emergency medical treatment.

Naltrexone

This medication started as a treatment to manage cravings and reduce the risk of relapse after alcohol use disorder (AUD) treatment; however, it was found to be effective at reducing the risk of relapse after opioid detox as well.

It was approved in 2010 by the FDA for this use under the prescription brands Vivitrol, ReVia, and Depade. Both ReVia and Depade are pills that should be taken once per day, while Vivitrol is a once-per-month injection administered by a physician.

Vivitrol

Vivitrol blocks the effects of opioids, including the illegal drug heroin and opioid pain relievers. The extended-release injectable drug is by prescription only and must be administered under a doctor’s care. It is given to patients who have completed opioid detox and need additional support to remain accountable while staying sober. The opiate blocker is also part of a program that uses psychosocial treatment.


According to Vivitrol’s website, after a person receives a dose of the medication, its blocking properties slowly decrease and go away over time. While it is active in the body, it blocks the effects of any heroin and other opioids, removing the user’s ability to get high from using the drugs. The added layer of protection against overdose can help recovering users stay on track.

Unlike naloxone, naltrexone binds long term to the opioid receptors in the brain and prevents opioid agonists from binding to these receptor sites at all, which limits or stops the sedative, euphoric, and breath-suppressing effects of opioid drugs like morphine, heroin, and oxycodone.

While the person is taking naltrexone, especially if they have received the month-long shot, they will feel fewer cravings for substances like opioids. If they do relapse back into opiate abuse, they will not feel intoxicated from the drugs. This helps the person examine their actions and, subconsciously, unlearn the association between taking opioids and feeling good.

Naltrexone may lead to reduced tolerance for opioid medications in the future, but it is not an intoxicating substance, has few side effects, and will not lead to diversion or abuse. There are some potential side effects.

  • Upset stomach, nausea, and vomiting
  • Diarrhea
  • Headache
  • Nervousness
  • Tiredness or trouble sleeping
  • Muscle or joint pain

Rarely, there may be complications associated with taking naltrexone, including liver injury, especially after alcohol abuse; infection or reactions at the injection site; and allergic reactions, including allergic pneumonia.

Using Opiate Blockers Effectively in Addiction Treatment

While both naltrexone and naloxone are important medications, they are not the main forms of medication-assisted treatment (MAT). Buprenorphine is the primary substance currently used in the U.S. to manage opioid detox by tapering the body off physical dependence on opioids. Methadone is also used for this purpose, although it is not used as often as buprenorphine.

Naloxone, by itself, is specifically used to temporarily stop opioid overdoses, while naltrexone is prescribed to some people after they have detoxed from opioids if they have struggled to remain sober after treatment. These opiate-blocking drugs are essential medications in the overall treatment of the opioid epidemic in the U.S.

How Medication-Assisted Treatment Addresses Opioid Use Disorder

Opioid blockers help people reach the point where they can consider getting the help they need to work through opioid dependence and addiction. Getting a second chance after a near-fatal overdose should spark a desire to seek additional help for a challenging time.

Medication-assisted treatment (MAT) has helped many people who are battling to overcome opioid use disorder, whether their illness followed heroin use or prescription opioid misuse. Cravings for opioids, which happen during the withdrawal period, along with other disruptive symptoms, can prompt users to pick up the drugs they were trying to leave behind when they decided to stop using.

MAT has been widely recognized for helping people in recovery stop their opioid use and help them maintain focus while navigating through the early stages of sobriety. The treatment approach combines FDA-approved medications and behavioral therapy so that physical, mental, and emotional aspects of opiate addiction are addressed.

SAMHSA  says the ultimate goal of a MAT program is for patients to fully recover from opiate use. It lists the following among the benefits of a MAT program:

  • Improved patient survival
  • Longer stays in addiction treatment
  • Less use of illegal opiate use and other criminal activity
  • Higher chance of recovering users finding a job and/or keeping one
  • Improved outcomes for pregnant women who have an opiate use disorder

Some observers have said that MAT programs could be likened to trading one drug dependence for another because medications are used to help people stay on track to sobriety. However, MAT supporters say the drugs are used along with psychotherapy and other supports to ensure patients are using the medications properly. 

They also say the benefits outweigh the negatives. This is because the medications treat the challenging physical and psychological symptoms of opioid withdrawal that create chemical imbalances in the body. “Medications used for MAT are evidence-based treatment options and do not just substitute one drug for another,” SAMHSA writes.

If you or a loved one is seeking recovery from opioid use disorder, consider entering a MAT program at an accredited facility. Staff at the facility can explain the treatment approach and assess whether it would be the right step for you and your family.

Arete Recovery can walk you through your options now. Give us a call so that we can learn more about your situation and what you need. We want to help, and we encourage you to get help as soon as you can.

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