Opioid antagonists help block opioid signaling in the central nervous system, and they include medications such as naloxone and naltrexone.

Your central nervous system has many different receptors on the surface of its cells. These receptors cue cells to perform an action when specific chemical messengers bind to them.

Opioid receptors are a natural part of your cellular makeup. Among many other things, the receptors influence your sensory perception of pain and facilitate your body’s response to hormones, drugs, and neurotransmitters.

Opioid antagonists are substances that can counteract opioid signaling, which helps your nervous system return to a state of balance.

Opioid antagonists bind to the opioid receptor site on a cell. While opioid agonists, such as morphine or oxycodone, produce a full response from the cell, an opioid antagonist generates no response.

The opioid antagonist then acts as a blockade against opioid agonists seeking the receptor site. The more opioid receptors blocked by an antagonist, the less you’ll feel the effects of an opioid.

Opioid antagonists are typically used to reverse an opioid overdose or treat opioid or alcohol use disorders.

Naloxone (Narcan) is an opioid antagonist used to reverse opioid overdoses. Naloxone starts rapidly binding to receptor sites after administration. Within several minutes, it can help restore normal breathing and can continue to block opioid signaling for up to 90 minutes while you get medical care.

Other opioid antagonists may not work as quickly but can block receptor sites longer or in targeted areas. These slower-acting medications are used for substance use disorder treatment.

Opioids and opioid antagonists also have a place in several other areas of medicine, particularly in the field of anesthesia. In some cases you may be given an opioid antagonist, such as alvimopan, after surgery to help with opioid-induced constipation.

Some doctors may also prescribe naloxone alongside opioids to help prevent an overdose.

Research also suggests opioid antagonists may be effective in the treatment of certain mental health conditions, such as schizophrenia and depression.

What drugs do opioid antagonists counteract?

Opioid antagonists can block the effects of common opioid drugs and opioid-stimulating substances such as:

Was this helpful?

Opioid antagonists are marketed under a variety of brand names for less than a handful of formulations.

While most of these medications have to be obtained through a doctor, some states will dispense naloxone without a prescription. If you have a loved one who takes opioids, carrying naloxone with you could save their life. Keep in mind that naloxone won’t have a negative effect if administered to someone without opioids in their system.

Other common opioid antagonists include:

  • Naltrexone: used for treating opioid and alcohol use disorders
  • Methylnaltrexone: used to treat opioid-induced constipation
  • Nalmefene: used to treat alcohol use disorder outside of the United States (it’s approved for reversing opioid overdoses in the United States but isn’t available yet)

What about buprenorphine?

Buprenorphine is a partial opioid agonist, which means that in some situations it can act like an antagonist. This is particularly true in the case of an overdose of another opioid.

If buprenorphine is given during an opioid overdose, it will bump other opioids off opioid receptors. The process reduces the activation of opioid receptors from full to partial, which can reverse overdose symptoms.

Naloxone is still the preferred rescue medication, while buprenorphine is more often used for treating opioid use disorder.

An important note about naloxone

Naloxone can help save someone’s life in the event of an opioid overdose, but it’s not a replacement for immediate medical attention. If you administer naloxone to someone, you’ll still want to consider calling 911 or local emergency services because naloxone will eventually wear off.

Learn more about handling an opioid overdose and how to call for help.

Was this helpful?

As with any medication, opioid antagonists can cause side effects.

One of the most common and immediate side effects is withdrawal. As access to opioids is suddenly cut off, you may experience:

  • headaches
  • blood pressure fluctuation
  • sweating
  • nausea
  • rapid heart rate
  • tremors
  • vomiting
  • body aches and pains
  • fever
  • chills
  • dizziness
  • anxiety

Withdrawal isn’t usually life threatening, but it can be extremely uncomfortable. A clinician can prescribe additional medications to help manage these symptoms.

Overall, opioid antagonists are considered safe medications. Other side effects outside of withdrawal include:

  • allergic reaction
  • injection site bruising or pain if an injectable form is used
  • drowsiness
  • headache
  • dizziness
  • vomiting
  • decreased appetite
  • muscle cramps
  • sleep disturbances
  • toothaches
  • muscle cramps
  • joint pain
  • cold or flu symptoms

Rare but potentially serious complications include:

  • injection site tissue death
  • liver damage or hepatitis
  • severe allergic reaction
  • depression
  • pneumonia

Risk of opioid overdose

Opioid overdose while using opioid antagonists may sound impossible, but it can happen.

If you take opioids while on an opioid antagonist, you’ll need to take more to experience the same effects you’re used to. Taking additional opioids while on an opioid antagonist can increase your risk of experiencing an unintentional overdose.

If you take opioids shortly after stopping the use of an antagonist, your opioid receptors will be extra sensitive to small doses of opioids. This sensitivity can similarly increase your risk of an unintentional overdose.

In addition to increasing overdose risk, the use of opioid antagonists can make you more sensitive to opioids in general once you stop taking the agonist, which means you might feel major effects even at smaller doses.

Opioid antagonists are substances that block the opioid receptors in your nervous system. They’re medications that can help reverse the effects of opioid overdose and treat substance use disorders.

Two of the most common opioid antagonists are the overdose-reversal drug naloxone and the treatment drug naltrexone.

Withdrawal symptoms are common when taking opioid antagonists. You may also experience side effects like injection site reactions, flu-like symptoms, or headaches.

In rare cases, opioid antagonists may cause more serious adverse effects such as liver damage or hepatitis.