Opioid Antagonist

What is an Opioid Antagonist?

Opioid antagonist is the mechanism of action of certain types of drugs that bind to opioid receptors and block them from being affected by opioid drugs. They are also called opioid receptor antagonists. These drugs are often used in the treatment of opioid addicts.

How Do Opioid Antagonists Work?

Opioid Antagonist

Opioid antagonists can be used to reverse the effects of an overdose.

According to the archives of the NIDA, “pharmacologically, a narcotic antagonist is a substance which has the ability to block the euphorigenic and dependence-producing properties of opioids.” These drugs work by attaching to the receptors that opioid analgesic drugs normally attach to and keeping them from working their effects on the person.

Some of them do not even activate these receptors and completely prevent the euphoric effects of opioid use. Some of them can even reverse the effects of opioids on the brain for a short period of time, and these are used for those individuals who have overdosed on opioids.

Who Needs Opioid Antagonists?

Someone who abuses opioids, is addicted to opioids, and/or has overdosed on opioid medications might need an opioid antagonist drug. Sometimes, these drugs are prescribed in treatment for addiction or as a relapse-deterring medication that is taken after detox. An opioid antagonist is also used in the hospital when a patient is brought in who is unresponsive due to an opioid overdose.

Examples of Opioid Antagonists

There are pure opioid antagonists and also medications that mix agonists and antagonists. Some examples of opioid antagonists are:


Naloxone is a medication that is given to patients who have overdosed on opioids. According to the NLM, it is used to “reverse the life-threatening effects of opiate (narcotic) overdose.” It can also be used to:

  • “Reverse the effects of opiates given during surgery” after surgery is over
  • Treat newborn babies and “decrease the effects of opiates received by the pregnant mother prior to delivery”

Naloxone, brand name Narcan, can save a person’s life if he or she is unresponsive after overdosing on opioids. While doctors use this medication in hospitals, there are also naloxone pre-filled auto-injection (Evzio) devices which people can buy and carry with them in case someone they care for is abusing or addicted to opiates. The NLM describes how this device should be used:

  • “The automatic injection device has an electronic voice system that provides step by step directions for use in an emergency.”
  • Do not worry about waiting for one step to finish to begin the next; time is of the essence here.
  • Call 911 first.
  • Then administer the drug by injecting it into “the muscle or under the skin of [the] thigh.”
  • Inject the drug through the clothing if necessary.
  • Wait with the person until help arrives and do not leave him or her alone for any reason.
  • If the person shows signs of the naloxone wearing off, use another automatic injection device and give the person another dose of naloxone.
  • “Additional injections may be given every 2-3 minutes if symptoms return before medical help arrives.”

Some of the side effects of naloxone are:

  • “Pain, burning, or redness at the injection site”
  • Hot flashes
  • Flushing of the skin
  • Sweating

If a person experiences other side effects, they might be dangerous. Someone who experiences them should call his or her doctor immediately. These are the dangerous side effects of naloxone:

  • “Rapid, pounding, or irregular heartbeat”
  • Hallucinations
  • Seizures
  • Opioid withdrawal symptoms
  • Unconsciousness

Some babies who are given naloxone injections may cry more than other babies their age and they may have “stronger than normal reflexes.” These symptoms should be monitored.

Opioid Agonist


According to the UIC, naltrexone, brand name ReVia, has a “longer duration of action than naloxone, a single oral dose blocks the effects of injected heroin (48 hrs).” It is often used in addiction treatment for opioid addicts and as a relapse deterrent for those who have finished with detox. Naltrexone is a highly effective opioid antagonist if it is used correctly and if the person using it is serious about getting off of opioids.

As stated by the Harvard Medical School, “an addict who takes naltrexone faithfully will never relapse, but most addicts simply stop using it, or refuse to take it in the first place.” Naltrexone works by:

  • “Blocking opiate receptors”
  • Neutralizing and sometimes even reversing the effects of opioids (such as euphoria, pain relief, and side effects)
  • Triggering “a withdrawal reaction in anyone who is physically dependent on opiates”

This medication is not easy on patients, which is why many of them refuse to take it. Because the withdrawal symptoms of opioids are painful and uncomfortable, many addicts and opioid dependent people continue to take the drugs just to avoid these symptoms. But, according to Harvard Medical School, “physicians and other middle-class patients who are highly motivated to get free of the opiate because they have so much to lose from a persistent addiction” would consider using naltrexone in order to get off opioids forever. The NLM states “naltrexone should not be used to treat people who are still using street drugs or drinking large amounts of alcohol” as it could cause severe withdrawal symptoms to develop.

Naltrexone is also used to treat opioid overdose. Some of the side effects of naltrexone are:

  • Loss of appetite
  • Tearing
  • Insomnia
  • Changes in energy
  • Pain in the muscles and joints
  • Drowsiness
  • Fatigue
  • Irritability
  • Anxiety
  • Nervousness
  • Dizziness
  • Headache
  • Nausea
  • Vomiting
  • Diarrhea
  • Cramping

If you are taking naltrexone and start to experience confusion, blurry vision, hallucinations or very intense diarrhea and vomiting, this could be a sign of serious effects caused by the naltrexone. You should consult your doctor immediately if you experience any of these symptoms.

Mixed Opioid Agonist-Antagonist

There are also other types of opioid antagonists that are mixed agonist-antagonists. These include:

  • Buprenorphine
  • Nalbuphine
  • Pentazocine

Buprenorphine is also used to treat opioid abusers and addicts.

Opioid antagonists are necessary for the treatment of opioid addiction, abuse, and overdose. Those who are prescribed them must also use them correctly, but they are more difficult to abuse than opioid analgesics or agonists.

If you abuse opioid antagonists, call 800-821-3880 now to speak with an addiction specialist about your treatment options

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