Naltrexone Side Effects: Guide to Management and Alternatives

Naltrexone is a U.S. Food and Drug Administration (FDA)-approved medication for treating alcohol use disorder and opioid use disorder. By blocking opioid receptors, naltrexone aids in decreasing cravings related to alcohol and opioid consumption. Naltrexone is not classified as a controlled substance.

Naltrexone is also prescribed off label in extremely low doses to manage chronic pain, inflammation, cancer, and mental health conditions.

Naltrexone and low-dose naltrexone differ in their uses, approved uses, mechanisms of action, and potential side effects.

What is Naltrexone?

Naltrexone is available in both an oral pill and an extended-release injectable form. It is used to treat alcohol and opioid use disorders, along with counseling and other behavioral health treatments. Naltrexone is not addictive and is also not a drug of abuse.

When naltrexone binds to opioid receptors, it blocks the euphoric and sedative effects of using opioids. It reduces opioid cravings.

Because naltrexone binds to opioid receptors, you should not take naltrexone until you haven’t used a short-acting opioid in the last seven days or a long-acting opioid in the previous 10 to 14 days. This is to reduce the risk of withdrawal symptoms.

According to the Substance Abuse and Mental Health Services Administration, it is very important to not take any opioids, illicit drugs, alcohol, sedatives, tranquilizers, or other drugs when taking naltrexone.

Naltrexone Uses

Naltrexone binds to opioid receptors in the brain. It reduces euphoria and other positive effects associated with using alcohol or opioids. It is used in combination with counseling, support groups, and behavioral therapy.

Naltrexone is used to treat alcohol use disorder

Naltrexone binds to opioid receptors and, therefore, blocks the release of endorphins, which cause the addictive effects and pleasurable feelings associated with consuming alcohol. This can help people decrease or even stop alcohol consumption.

Naltrexone can treat alcohol use disorder after a person has completed the alcohol detox process. Taking alcohol and naltrexone together can cause nausea and vomiting.

Naltrexone significantly reduces alcohol relapses, the frequency and quantity of alcohol people consume, and alcohol cravings. The treatment duration varies depending on an individual’s goals and the recommendations of their healthcare provider.

Naltrexone is used to treat opioid use disorder

Opioid use disorder is a chronic illness. Naltrexone binds to opioid receptors in the brain. By blocking these receptors, naltrexone prevents opioids from exerting their effects, including the euphoria associated with opioid use.

Naltrexone can be used to prevent opioid misuse relapse as part of a medically supervised treatment program. While naltrexone is safe and effective, it requires people to commit to abstinence before using it.

Common Side Effects of Naltrexone 

Naltrexone, when taken at higher doses to treat alcohol use disorder or opioid use disorder, can have physical and psychological side effects. However, a systematic review of many clinical studies found no evidence of an increased risk of serious side effects for people taking naltrexone compared to people taking the placebo.¹

Physical Side Effects

Physical side effects associated with naltrexone use include:

• Difficulty sleeping
• Anxiety
• Nervousness
• Abdominal pain or cramps
• Nausea
• Vomiting
• Low energy
• Joint and muscle pain
• Headache

In clinical trials, more than 10% of people taking naltrexone experienced these side effects.

Less common physical side effects associated with naltrexone use during clinical trials include:

• Decreased appetite
• Diarrhea
• Constipation
• Increased thirst
• Dizziness
• Skin rash
• Delayed ejaculation
• Decreased potency
• Chills

Side effects reported after clinical trials include:

• Chest pain
• Fatigue
• Hot flashes
• Malaise
• Changes in blood pressure
• Tremor
• Fast or irregular heartbeat
• Indigestion
• Vision abnormalities

Psychological Side Effects

Psychological side effects associated with naltrexone use include:

• Increased energy
• Feeling down
• Irritability
• Agitation
• Confusion
• Euphoria
• Hallucinations
• Nervousness
• Abnormal thinking

This is not the complete list of side effects known to occur with naltrexone use. Consult with your doctor if you are experiencing any persistent or concerning side effects.

Low-dose naltrexone is believed to temporarily block opioid receptors. In response, the brain increases the production of endorphins and enkephalins, which are natural opioids produced in the body. These natural opioids can have pain-relieving and anti-inflammatory effects throughout the body.

Low-Dose Naltrexone (LDN) Uses

Low-dose naltrexone binds to opioid receptors, just like high-dose naltrexone. Opioid receptors are found all over the body, including the brain, spinal cord, gastrointestinal system, and lymphocytes (immune cells).

With a low naltrexone dose, the receptors are blocked for about one hour, and the medication effects last between 4 and 6 hours. When the opioid receptors are blocked, your brain produces more opioids. After a dose of low-dose naltrexone, naturally produced opioids can have their effect for the next 18 to 24 hours, providing steady pain relief and decreasing inflammation.²

Low-dose naltrexone has many potential uses, and it is undergoing testing as a possible treatment for chronic diseases such as fibromyalgia, chronic fatigue syndrome, and multiple sclerosis.^3,4,5

Additional uses for low-dose naltrexone include:²

• Decreases pain
• Decreases inflammation
• Relieves fatigue
• Supports healthy immune function
• Supports brain health

What Are Low-Dose Naltrexone Side Effects?

Side effects from low-dose naltrexone are uncommon. If they occur, they are typically mild. Side effects reported with low-dose naltrexone include:⁴

• Altered mood
• Difficulty sleeping
• Headaches
• Joint pain
• Nausea
• Nightmares
• Prolonged erections
• Unusual dreams
• Weight loss

Naltrexone researchers report that their patients tolerate low-dose naltrexone very well. The most common side effects that patients report are vivid dreams (37% of patients) and nightmares. In many cases, these decrease over time.⁴

Do Naltrexone Side Effects Go Away? 

More research is needed to fully understand naltrexone side effects, especially with low-dose naltrexone.

Naltrexone side effects vary between people and the dosage used. For example, some people have increased energy and insomnia when taking low-dose naltrexone and, therefore, take their daily dose in the morning. Others experience fatigue or dizziness and prefer to take low-dose naltrexone at night. Talk to your doctor about any side effects you may experience. They may recommend a change in dose or medication intervals.

Drug Interactions

Even at low doses, don’t take naltrexone with certain pain relievers such as tramadol, fentanyl, oxycodone, and many others. Tell your doctor if you have used any opioid medication in the past 7 to 10 days. Taking naltrexone with an opioid can cause dangerous naltrexone interactions and side effects, as it can precipitate severe and rapid withdrawal symptoms.

Naltrexone should not be taken with alcohol. Naltrexone will reduce alcohol cravings and the “buzz” you may experience when drinking alcohol, but it will not keep you from becoming impaired.

Before taking naltrexone, tell your doctor and pharmacist about all medications, supplements, and herbal products you are taking to prevent potential drug interactions.

Can You Overdose on Naltrexone?

Limited information is available on the effects of naltrexone overdosage. In one study, people received 800 mg of naltrexone daily for seven days. They reported no signs of toxicity.

Higher doses may cause liver inflammation or damage. There are also reports of depression, suicidal ideation, and suicidal attempts after using high-dose naltrexone.⁵

Take naltrexone exactly as prescribed. Call poison control if you overdose on naltrexone or any other medication.

Use Naltrexone as Prescribed

Research suggests that low-dose naltrexone has quite different actions in the body from high-dose naltrexone. It is important to take your naltrexone dose as prescribed. Contact your doctor if you have any side effects or concerns with taking your medication.

Alternatives to Naltrexone

The naltrexone options available will depend on why you are taking naltrexone. For example, some people take low-dose naltrexone to reduce food cravings and promote weight loss.

If you are taking low-dose naltrexone to help manage your weight and you are experiencing side effects, contact an Invigor Medical treatment specialist. Your Invigor Medical healthcare provider may suggest another medication to help manage your food cravings or for weight management.

When to Seek Medical Attention

Seek medical attention if you combine opioid use and naltrexone, as you may experience dangerous withdrawal effects.

Contact your doctor if you are unable to control alcohol cravings while taking naltrexone.

Contact your doctor or seek emergency care if you experience suicidal thoughts, feel depressed, or have any persistent or concerning side effects while taking naltrexone.

Overall, low-dose naltrexone appears to be a safe and effective medication, but it should only be taken after consulting with your doctor. Fill your low-dose naltrexone prescription at a licensed pharmacy.

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