• Addiction & recovery

Is Naltrexone an Opioid?

Vanessa de la Cruz, MD

January 17, 2022


Naltrexone is an opioid antagonist (inhibitor) approved by the U.S. Food and Drug Administration (FDA) for the treatment of opioid use disorder (OUD) and alcohol use disorder (AUD). It helps people in recovery maintain long-term abstinence by blocking the intoxicating effects of alcohol and opioids and reducing the cravings for such substances. Naltrexone is available as a pill (ReVia, Depade) or an extended-release intramuscular injectable (Vivitrol). Naltrexone is utilized as a part of a comprehensive treatment program that includes behavioral therapies, counseling, and an aftercare support system


Naltrexone for Opioid Use Disorder

Naltrexone, as a medication for opioid use disorder (MOUD), works by binding to opioid receptors in the brain and blocking the effects of opioids. This function helps reduce opioid cravings and blocks the intoxicating effects of opioids to reduce the risk of relapse. 

Naltrexone treatment is generally recommended for individuals who have stayed clear of all opioids for the past 10-14 days. This measure is taken to avoid generating precipitated withdrawal, a sudden onset of intense withdrawal symptoms. 


Naltrexone for Alcohol Use Disorder 

Naltrexone, as a medication for alcohol use disorder (MAUD), works by binding to the endorphin receptors. This function helps reduce cravings and increases the likelihood of long-term abstinence. Unlike disulfiram, naltrexone does not make you sick during alcohol consumption. Hence naltrexone treatment can be initiated in active alcohol users. However, most healthcare professionals wait until the completion of alcohol detox to avoid potential side effects such as nausea or vomiting. 

Since naltrexone negatively interacts with opioids, it’s important even for individuals deciding to take naltrexone for AUD treatment to inform their healthcare practitioner of any opioids or opioid-containing medications currently being taken to prevent the risk of sudden opioid withdrawal symptoms. A few other medications that interact with naltrexone are codeine, hydrocodone, and diarrhea medications such as diphenoxylate. 


Is Naltrexone a Controlled Substance?

The U.S. Drug Enforcement Administration (DEA) has not classified naltrexone as a controlled substance. However, it’s currently available only through prescription by any healthcare practitioner licensed to dispense medications. The pill form is prescribed daily to be taken at home or in a clinical setting, while the injectable form is administered once a month by a healthcare provider. Individuals interested in the extended-release form of naltrexone (Vivitrol) are required to partake in a Risk Evaluation and Mitigation Strategy (REMS) to ensure that the benefits of the medication outweigh its potential risks. 


Is Naltrexone a Narcotic?

Although naltrexone binds to opioid receptors in the brain, it does not activate them like buprenorphine and methadone. Hence they are not considered a narcotic medication. This feature makes naltrexone a relatively safe medication with a low potential for misuse. According to the National Institute on Alcohol Abuse and Alcoholism (NIAAA), naltrexone is a non-habit-forming medication that does not induce physical or psychological dependence and addiction. 

The long-term use of naltrexone rarely causes any considerable health complications when used as prescribed. However, naltrexone is reported to cause certain side effects in some individuals during the initial stage of treatment. 


Side Effects of Naltrexone 

Side effects of naltrexone are generally mild and dissipate on their own. However, if any side effects persist or worsen, it’s important to contact a healthcare provider immediately.

Some of the common side effects of naltrexone are:

  • Nausea
  • Vomiting
  • Sleepiness
  • Headache
  • Dizziness
  • Loss of appetite
  • Abdominal pain
  • Painful joints
  • Muscle cramps
  • Insomnia
  • Toothache
  • Cold symptoms

It’s important to talk to your healthcare provider before discontinuing naltrexone treatment due to side effects. Your physician can address the issue by adjusting your dosage or prescribing an alternative medication. 

Although rare serious side effects are possible with naltrexone, these side effects are a medical emergency requiring immediate medical attention.

Severe side effects of naltrexone may include:

  • Pneumonia
  • Depressed mood
  • Serious allergic reactions (such as swelling of the face, eyes, mouth or tongue, skin rash, and chest pain)
  • Liver damage or hepatitis (symptoms include dark urine, stomach-area pain lasting for more than three days, and yellowing of the whites of the eyes)
  • Severe injection site reactions 


Sudden Opioid Withdrawal Syndrome

In addition to the risk of side effects, naltrexone can cause a condition known as sudden opioid withdrawal syndrome (SOWS) or precipitated withdrawal symptoms. This condition is caused when naltrexone is used while opioids are still in your system. Because naltrexone binds to opioid receptors in the brain and blocks their effects instantly, taking it when there are traces of opioids in the bloodstream can cause severe opioid withdrawals.

Sudden opioid withdrawal includes symptoms such as:

  • Dilated pupils 
  • Agitation 
  • Anxiety
  • Muscle aches
  • Teary eyes
  • Sweating 
  • Yawning 
  • Insomnia 
  • Diarrhea
  • Cramping 
  • Goosebumps 
  • Nausea
  • Vomiting 

Individuals are advised to wait for at least seven days since the last use of short-acting opioids and 10-14 days for long-acting opioids before receiving naltrexone treatment. Individuals must also provide their healthcare provider with a list of all prescription, herbal, and over-the-counter medications currently in use as they may contain opioids.


Risk of Overdose While on Naltrexone

Although naltrexone itself does not hold the potential to cause an overdose, opioid overdose is a possibility when individuals take large doses of opioids to overcome the blocking effect of naltrexone. The risk of opioid overdose remains the same during and after naltrexone treatment due to the increased sensitivity to opioids. 

Opioid overdose is a medical emergency that requires immediate medical attention. In the event of an opioid overdose, if it is available, administer Narcan/naloxone to the person who has overdosed and call 911 or the National Poison Control Center immediately. If the person who overdosed remains unresponsive, ensure to put them in the recovery position to prevent them from choking on their vomit. And stay with them until the paramedics arrive. 

Naltrexone is an effective treatment in helping people overcome their OUD and AUD. Naltrexone is best combined with other elements of a comprehensive treatment program, such as counseling, behavioral therapies, and aftercare programs to ensure successful, long-term abstinence from opioids and alcohol.

If you are seeking help with your loved one’s addiction, contact us today or complete our quick contact form below, to speak with an addiction treatment specialist.

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