Naltrexone Side Effects

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With the prevalence of addiction going up with every passing day, experts are coming up with newer ways to combat this issue. One of the most successful methods of handling addiction is medication-assisted treatment (MAT), which involves using controlled medications in a safe environment to combat addictive behaviors. Naltrexone is one of the most popular medications that experts use to help addicts overcome their destructive substance use patterns. Available under various brand names, such as Vivitrol and ReVia, this medication can particularly help people with opioid and alcohol use disorders. Despite being an active anti-addiction agent, many people end up experiencing various naltrexone side effects on their own.

If you or someone you know has recently started their addiction journey with the help of naltrexone, familiarizing yourself with what to expect regarding side effects is important. This knowledge will help you anticipate and prepare for what may happen soon and understand when and how to seek help for it.

An Overview of Naltrexone Use

Naltrexone has shown great potential in assisting people overcome various addictions. This unique drug works as an opioid antagonist by binding to opioid receptors in the brain and blocking other addictive substances to attach with them, and causing euphoria. Blocking these pleasureful feelings, helps to recover addicts gain better control over their cravings for the underlying addictive substances. Many people have been using other drugs, such as buprenorphine and methadone, for similar purposes. However, naltrexone remains superior to these alternative medications as it suppresses the opioid receptors in contrast to opioid activation caused by the other two drugs.

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Naltrexone is primarily available in two forms: an injection form called Vivitrol and a pill form called ReVia. Either form of this medication cannot lead to any high, minimizing the risk of becoming dependent. However, remember that naltrexone’s ability to suppress opioid-induced high has a certain limit, and certain people may cross it by using a very high dose of alcohol or opioid. While doing so can reverse or override naltrexone’s blocking effects, it may also lead to overdoses.

Side Effects of Low-Dose Naltrexone

Despite being an amazing and effective medication to control and reverse addictions, naltrexone can sometimes induce its side effects, including the following:

Allergic Reaction

As with any other medication, some people may develop an allergic reaction following the consumption of naltrexone. Experts are not sure how often or frequently this reaction may occur, but they warn all new users to watch out for the following signs and contact a doctor immediately if they develop it following a dose of naltrexone:

  • Itchiness
  • Skin rash
  • Flushing
  • Hives

In some cases, some people may end up experiencing more severe allergy symptoms, such as the following:

  • Labored breathing
  • Chest pain
  • Swelling of mouth, throat, or tongue
  • Dizziness
  • Swelling under the skin, especially in lips, hands, face, feet, and eyelids

It is crucial to seek medical help for any allergic reaction right away or it may progress to become life-threatening.

Withdrawal Symptoms

Experts warn patients to avoid taking opioid medications as long as they are on naltrexone or Vivitrol. Sometimes, it is crucial to stop all opioid medications at least 7 days before starting treatment with naltrexone. Using both substances together can lead to a risk of withdrawal with various uncomfortable symptoms varying from mild to severe. Some people may even require hospitalization or 24/7 expert supervision to overcome these naltrexone side effects

Low Mood or Suicidal Thoughts

In some people, using naltrexone may lead to depressed thoughts or suicidal tendencies. These altered mood changes can be serious and may force a person to engage in self-harming behaviors. Watch out for the following symptoms and get in touch with a doctor before they get serious:

  • Feeling sad or hopeless
  • Excessive crying
  • Not feeling interested in doing things you usually enjoy
  • Feeling more angry or aggressive than usual
  • Sleeping a lot more or a lot less than usual
  • Having thoughts of hurting yourself

Liver Damage

One of the long-term naltrexone side effects includes direct liver damage, such as liver swelling or hepatitis. Due to this risk, a doctor may monitor your liver enzymes, including aspartate aminotransferases (AST) and alanine aminotransferases (ALT), to monitor your liver health. Additionally, a doctor may ask you to keep an eye on your general health and look out for the following symptoms indicative of liver damage:

  • Dark urine
  • Yellowing of eyes or skin
  • Pale stools
  • Belly pain


Certain people may experience intense nausea or throwing up, especially after receiving the injectable form of naltrexone. This side effect is particularly prevalent in first-timer users and, fortunately, goes away in a few days without requiring intervention. Those with severe, persistent nausea must contact a doctor to sort it out immediately.


Individuals new to using naltrexone may respond negatively to the medication by developing diarrhea. This symptom is indicative of an obvious gastrointestinal upset and can expect to happen to anyone trying out a medication for the first time. Like nausea, this gastrointestinal symptom is also likely to subside within a few days on its own.


Some people may report feeling headaches after taking naltrexone. However, these headaches are mostly mild and tolerable, requiring no intervention. If your headache is slowly becoming bothersome, talk to an expert about the potential solutions to keep it under control.

Injection Site Reactions

People who receive naltrexone injections or Vivitrol may develop a reaction at the injection site. This reaction may involve redness, bruising, or swelling at the sight where the medicine was injected. Fortunately, these symptoms are rare and very mild in most people; however, some people may rarely develop severe reactions that require medical help.

Risk of Opioid Overdose

If you are starting a naltrexone program, it is crucial to educate yourself about how this medication can increase your sensitivity to opioids, putting you at a higher risk of experiencing an overdose. In this case, an overdose may occur in the following two ways:

Naltrexone works by blocking the effects of opioids, such as heroin or oxycodone. An addict may try to overcome this block by taking their opioid substance in larger amounts than they usually consume, eventually developing signs of an overdose. 

The blocking effect of naltrexone is not permanent and wears off with time. However, using this drug even once can make a user much more sensitive to the effects of opioids, even at the same doses that they have always been using. As a result, these drugs may affect the body more severely, leading to overdoses.

Tips to Avoid Naltrexone Side Effects

Experts recommend following the tips mentioned below to avoid the side effects of low-dose naltrexone:

  • Take naltrexone exactly how a doctor prescribes. Do not take less or more than the recommended dose, as it may render it ineffective or cause liver damage, respectively.
  • Steer clear of opioids throughout your naltrexone program, as doing so may make you lose the benefit of entering the program altogether.
  • Always seek comprehensive psychotherapeutic and social measures side by side as you continue taking naltrexone to beat addiction once and for all.
  • Do not try to increase the dose of your opioids to override the blocking effect of naltrexone, as it may lead to an overdose.
  • Always carry some identification that can alert medical personnel about your naltrexone use.
  • If you start experiencing any abdominal pain that persists for a few days or notice your skin getting yellow, get in touch with a doctor immediately to get your liver health checked.
  • Naltrexone may affect your ability to operate machinery or drive. Hence, do not engage in these activities if you are under the medication’s influence.
  • Talk to your doctor before combining naltrexone with other prescription-based or over-the-counter medications to minimize cross-interactions.

Supporting a Loved One During Naltrexone Program

Individuals beginning their medication-assisted program with naltrexone will require practical and emotional support from their loved ones. Hence, if someone around you is due to begin one of these programs, discuss the type of support they will need and what you can provide. This discussion must also include your role in keeping in touch with their doctor and informing them of any problems during treatment.

Some other ways in which you can support someone undergoing a naltrexone program include the following:

  • Commit yourself to supervise the naltrexone dose for your loved one throughout the duration of treatment
  • Attend family or couples counseling sessions, if needed
  • Encourage your loved ones to develop healthy support networks with others experiencing similar struggles and participate in as many positive and healthy activities as possible, such as exercising or taking a class
  • Educate yourself about how to handle a situation involving an overdose
  • Accompany your loved one with their regular appointments, such as with their counselors or doctors

Remember that supporting a person undergoing a naltrexone program can be challenging. As you continue supporting your loved one, don’t neglect self-care and seek help if needed.


How severe will be the side effects of using naltrexone for addiction?

The severity of side effects secondary to naltrexone use can vary from one person to another. The severity and nature of these side effects can depend on the following factors:

The amount of naltrexone you are consuming

Whether you are a first-time user or have already used it before

Your current health status, body weight, and size

Whether you are taking other drugs with it

What to avoid when taking low dose naltrexone?

Experts recommend avoiding certain substances as long as they are taking low dose naltrexone. These substances include the following:

  • Any medication that may induce sedation as a side effect, such as antihistamines, antidepressants, anti-anxiety medications, and anti-psychotics
  • Disulfiram, a drug commonly used to manage alcohol abuse
  • Any medication that contains any amount of opioid, such as hydrocodone, codeine, morphine, methadone, oxycodone, and loperamide
  • Any pain relievers, cough, and cold preparations, or anti-diarrheal medications that include opioids

Lastly, ensure that you do not take any recreational drugs and alcohol while taking naltrexone.

Can using naltrexone cure my addiction?

Addiction is a long-term illness that is fortunately possible to manage. Although experts do not have an immediate cure for it, there are plenty of ways to gradually recover from it and enjoy high-quality life. Due to its complex nature, a full recovery requires a combination of different approaches, and medication-assisted treatment is one of them. Hence, it would not be right to say that using naltrexone can cure an addiction completely. However, its appropriate use can enable a person to fight their underlying addiction much better and more comfortably.

Who should avoid taking naltrexone?

While naltrexone is an amazing option to help people overcome opioid and alcohol use disorders, certain people should avoid taking it for safety reasons. These include individuals who are:

  • Going through an active opioid withdrawal
  • Dealing with a kidney or liver issue
  • Currently abusing illicit opioids
  • Breastfeeding or nursing
  • Detoxing from alcohol

Is naltrexone addictive?

Naltrexone is not addictive but can help users overcome addictions to certain dangerous substances, such as alcohol and opioids. This non-addictive nature of naltrexone is also why experts prefer prescribing it to addicts instead of other alternatives, such as methadone. The only drawback of naltrexone is its side effects, most of which fortunately remain manageable.

What are naltrexone weight loss side effects?

Many experts recommend using naltrexone to help people lose weight, as the medication can regulate appetite and insulin sensitivity in the body. This apparently positive effect may turn into a side effect in people using this medication to overcome addiction without intending to lose weight.

How long do naltrexone side effects last?

The side effects of naltrexone may go away within a few days of using this medication.

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