Side Effects of Naltrexone To Be Aware Of


Naltrexone is a prescription drug doctors recommend to people struggling with different types of opioid addiction. It’s a part of pharmacotherapy, which shouldn’t be carried alone but combined with behavioral therapy and detoxification.

The Food and Drug Administration has approved naltrexone as a valid and safe treatment for opioid and alcohol use disorder. It’s tested and effective, but that doesn’t mean this drug has no unwanted effects.

We explain the possible side effects of Naltrexone, which a healthcare provider should warn patients about.

What Are the Side Effects of Naltrexone?

When taking naltrexone, patients might feel some unwanted effects. The risk exists, but it’s not a guarantee they’ll experience any of these. Just in case, a healthcare professional should introduce their patients to the side effects of this medical treatment and encourage them to seek medical attention.

Unwanted actions of naltrexone can occur as:

  • Mild side effects
  • Severe side effects
  • Long-term side effects

1. Mild Side Effects

Patients taking naltrexone for the first time might feel minor discomfort during treatment. In most cases, these are nausea, headache, abdominal pain, stomach cramping, and unusual tiredness. These symptoms don’t require medical treatment since they usually don’t last more than a few days (as we need some time to adapt to naltrexone).

Less common mild side effects are gastrointestinal issues, like diarrhea and constipation. Some people might feel increased thirst, while others can have problems with appetite. Patients can also experience cold-like symptoms, sinus problems, blurred vision, swollen eyes, and buzzing in their ears.

In the case of naltrexone intramuscular injection, swelling can appear on the injected spot. It can also become irritated, stiff, and painful. Another injection site reaction can be the occurrence of nodules, but it happens rarer (in less than 10% of cases).

Naltrexone can also affect the patient’s mood and behavior, leading to minor mental issues like lethargy, anxiety, or problems with sleeping. Men might face sexual problems and loss of libido. These should pass in a few days, but in case these symptoms last long or disrupt the patient’s activities, they should seek medical help.

2. Severe Side Effects

Severe side effects require medical help, especially if patients have serious allergic reactions to naltrexone. These can be a skin rash, swellings on the face, mouth, or tongue, chest pain, and breathing issues.

Some patients who were given naltrexone injections have reported severe reactions in the injection spot. They’ve spotted local inflammations, blistering, and numbness, while there were also people who experienced necrosis (tissue death). The latter symptom requires immediate medical action and surgical treatment.

People struggling with addiction might experience mood swings and mental changes. If they feel depressed, confused, or experience hallucinations after taking naltrexone, they should seek urgent medical help.

During naltrexone treatment, some patients can feel opioid withdrawal symptoms, especially if they didn’t manage to stay clean for at least 10 days before starting this treatment. They can feel stomach pain, anxiety, rapid or impaired heartbeat, etc. In case patients fail the naloxone challenge test and start feeling these symptoms, they should seek medical help.

3. Long-Term Side Effects

Naltrexone doesn’t cause opioid dependence, as it’s not a habit-forming drug. In that regard, there are no long-term side effects that can be related to its use. When patients take this drug and complete the treatment program as described, there’s no major risk to their health.

However, people with a diagnosed liver disease might face severe, long-term effects of naltrexone treatment. In patients with acute hepatitis or liver damage, higher doses of naltrexone can be harmful and contraindicated.

Patients with liver disease must inform their healthcare providers about this so they can adjust the treatment to their health condition. Doctors need to monitor patients’ liver function during naltrexone treatment with regular blood tests to know when to discontinue it and prevent long-term damage to their health.

What Patients Should Know Before Starting Naltrexone Treatment

Naltrexone belongs to opioid antagonists, as it acts on receptors to reduce opioid cravings. It blocks their interaction with illicit substances and narcotic drugs, so an addict won’t feel all their “good” effects, like being drowsy or high.

Naltrexone Dosage

Naltrexone comes in two forms: oral pills and injectables. Its dosage and intake method will depend on the type of opioid use disorder treated.

Oral Naltrexone

For treating alcohol dependence, the optimal naltrexone dose is 50 mg a day. It can be taken as a single pill every day, and alternative dosing schedules can be 100 mg every second day or 150 mg of naltrexone every third day.

In the case of opioid use disorder, doctors usually prescribe 25 mg of naltrexone (half a pill) in the initial treatment stage. If patients feel no opioid withdrawal symptoms, they can receive a maintenance dose of 50 mg of naltrexone.

Lower doses of naltrexone (about one-tenth of the regular dose) can benefit people diagnosed with cancer, Crohn’s disease, fibromyalgia, and a few other severe conditions. This off-label use of low-dose naltrexone isn’t FDA-approved yet and requires further research, but treatment benefits are apparent and recognized.

Naltrexone Injection

Naltrexone injectables can help people who struggle with addiction due to drug abuse. They get a single dose of 380 mg of naltrexone, which is enough to block opioid receptors from interacting with opioids for about a month (four weeks).

Missed Dose

In case patients forget to take this medicine, a missed dose should be taken as soon as possible. If it’s near the time of the next dose, taking it isn’t necessary since they should just continue with a regular dosing schedule.

Who Can/Can’t Take Naltrexone

People on naltrexone should refrain from alcohol, painkillers, and street drugs for at least ten days before the treatment. If not, taking this antagonist can trigger harsh opioid withdrawal symptoms.

Naltrexone isn’t a treatment that people with liver and kidney disease should use without medical supervision. As it takes time for this substance to get out of the body, it passes through these organs and interferes with their already-disrupted functioning. They need to let doctors know about their conditions so they can adjust the dose and follow the treatment course.

Also, pregnant or breastfeeding women should inform healthcare professionals about their conditions before taking naltrexone. There has been limited research on taking this medication during pregnancy or breastfeeding, which doesn’t provide enough evidence for naltrexone effects on humans.

Naltrexone Half-Life

To avoid taking more naltrexone than prescribed, patients should be familiar with the drug’s half-life. It shows how much time it takes for the drug to get out of the body and for how long this substance can be detected in the patient’s urine.

In the case of naltrexone pills, a half-life is anywhere between four and 12 hours, depending on the dosage schedule. Naltrexone injectables have extended action, meaning their half-life is much longer — five to 10 days.

Naltrexone Drug Interactions

During naltrexone use, patients should avoid opioid drugs of any kind, both legal and illegal. They should also refrain from taking non-prescription painkillers, as some of these drugs act on opioid receptors. Since naltrexone blocks their action, these pain medications will be useless.

Naltrexone also has recorded interactions with some diarrhea medications, probiotics, and over-the-counter cough remedies containing dextromethorphan. It shouldn’t be mixed with other medications used for treating opioid addiction, especially those with different mechanisms of action.

Frequently Asked Questions

What Happens When I Quit Naltrexone?

Patients quitting naltrexone won’t feel any withdrawal symptoms since naltrexone isn’t an opioid itself. The chance of abusing this drug is minimal as it’s not addictive. It means it won’t have effects like after taking drugs or drinking alcohol, even in people who don’t have physical dependence on these substances.

Is Opioid Overdose Possible While Taking Naltrexone?

As naltrexone blocks the effects of opioid drugs and alcohol, it should reduce cravings. People struggling with severe addiction might take higher doses of illicit substances or opioid medications to overcome these blocking effects. That leads to opioid overdose.

Is Naltrexone a Controlled Substance?

Naltrexone is an FDA-approved drug, but it’s not marked as a controlled substance as it doesn’t have habit-forming effects.

To Conclude

Patients should be familiar with the side effects of naltrexone before taking this medication. That way, they can discuss the best treatment options with their doctors to ensure its efficiency and take precautionary measures to prevent unwanted actions.


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