How Does Naltrexone Work? Simply Explained


Naltrexone is an opioid antagonist that works by stopping opioid effects by binding to the receptors that opioids are supposed to attach to.

The good news is that naltrexone itself doesn’t activate those receptors, which takes the addiction probability out of the formula.

However, there are a few side effects and necessary precautions while using naltrexone. If not used correctly, naltrexone can indirectly cause an opioid overdose that could be fatal.

Here’s how naltrexone works in detail.

The Opioid System: An Inside Look

Before understanding the actual mechanism of naltrexone, we need to know how the human opioid system works.

It’s a complex system of receptors, neurotransmitters, and pathways. Together, they regulate various emotional functions like pain perception, reward, and mood.

When the body secretes endogenous opioids like endorphins, enkephalins, and dynorphins, it controls the emotional response elicited by these naturally occurring chemicals.

In some cases of extreme pain, doctors prescribe “exogenous” opioids like hydrocodone and morphine. Such opioids have a higher potency for pain relief, which “lights up” the reward pathway in the nervous system. This improves the overall condition and mood of the patient.

Addiction, or opioid use disorder, occurs when the patient gets used to the euphoric feeling they get from external opioids.

That’s when naltrexone comes into the picture.

What Is Naltrexone and How Does Naltrexone Work?

Naltrexone hydrochloride, known as naltrexone, is a prescription medication that’s primarily used in substance abuse treatment for Opioid Use Disorder (OUD), commonly known as opioid dependence.

It’s an opioid receptor antagonist, which means it competes with exogenous opioids (like prescription or illicit drugs) by binding to the same receptors. This stops the mechanism of actions of those addictive opioids by blocking them from achieving their effect.

Despite binding to the same opioid receptors, naltrexone doesn’t activate said receptors, which means the drug itself is not addictive and doesn’t cause any opioid withdrawal symptoms.

While the exact mechanism of action is yet to be known, naltrexone is also used in treating Alcohol Use Disorder (AUD) to reduce alcohol cravings.

How to Use Naltrexone?

Naltrexone is available in both oral naltrexone pills and injectable forms. The pill is 50 mg, and it’s taken once every 24 hours. The injectable form is given once a month. Its dose is 380 mg.

It’s important to understand that naltrexone treatment is a type of medication-assisted treatment (MAT). It doesn’t directly treat opioid addiction; it’s used in combination with counseling to help patients deal with their opioid addiction.

That’s why naltrexone doesn’t work for every patient. Since it doesn’t directly cure the addiction, the patient must be aware of their addiction and willing to take the medication alongside their therapy.

Naltrexone can’t be used if the patient is still struggling with withdrawal symptoms, which may last for around a week and up to 10 days after the last dose of opioids. The drug is used as the “second step” after the symptoms have worn off to help the patient proceed through their treatment.

That “help” comes in the form of making opioids less desirable for the patient, as their effect is nearly entirely blocked since they can’t bind to the receptors anymore.

All of this should be done with a doctor’s supervision, as naltrexone can cause drug interactions with various other drugs, like some OTC drugs, prescription drugs, and opioid analgesics.

Is Naltrexone Dangerous?

No, naltrexone is a generally safe drug as long as it’s used under a doctor’s supervision. Those who tend to forget whether they’ve taken the pill can also rest assured, as the patient can safely tolerate three 50 mg pills a day without serious side effects.

However, while naltrexone itself is safe, it can indirectly cause the patient to overdose..

Naltrexone blocks the effects of exogenous opioids by binding to their receptors. If the patient relapses and goes back to taking opioids, they won’t get that satisfying feeling they usually get because opioids won’t work.

Since addiction can alter the patient’s judgment, some patients may take extra doses of opioids in an attempt to get the feeling they seek, leading to a fatal opioid overdose.

Does Naltrexone Have Side Effects?

All synthetic medications have side effects, and naltrexone is no exception. There are common and uncommon side effects.

Common Naltrexone Side Effects

Many patients who take naltrexone for the first time may experience:

  • Reduced appetite for food
  • Random body pains, especially around the mouth and teeth
  • Muscle cramps
  • Trouble sleeping and some headache
  • Nausea, dizziness, and vomiting.

Most of these side effects should subside as the body gets used to the drug, especially nausea and vomiting.

Uncommon Naltrexone Side Effects

In less common scenarios, the patient may experience:

1. Liver Damage

Naltrexone gets metabolized in the liver, so it requires a healthy liver to be broken down and removed from the blood.

Prolonged use of naltrexone or using naltrexone with an unhealthy liver may lead to:

  • Jaundice (which manifests as yellow eyes)
  • Dark urine
  • Pain under the stomach

2. Allergic Reactions

Some patients may exhibit allergic reactions of varying degrees upon taking naltrexone for the first time. It’s essential to report any of the following reactions to your doctor:

  • Swelling in the face or around the eyes
  • Skin rash
  • Skin blisters

3. Skin Reactions at the Injection Site

Putting aside the skin reactions that may result from faulty injections, a patient who takes injectable naltrexone may experience:

  • Lingering pain at the injection site
  • Open wounds (if the patient is allergic to the medication)
  • Hard areas or raised lumps

Final Words

Naltrexone is a relatively safe drug that’s commonly used to help the patient get rid of their opioid addiction by reducing cravings. It’s available as pills or extended release monthly injections, and is usually taken after the withdrawal symptoms have started to wear off.

It works by making the effect of the addictive opioids less desirable by binding to the opioid receptors.

If you or anyone is about to undergo naltrexone therapy, it’s paramount to keep an eye out for any side effects mentioned above.

Recovery from addiction to opioid pain medication is a challenging journey. Book an appointment with one of our certified telemedicine doctors today to know what your next step is.


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