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Naltrexone Side Effects - What You Should Know

Naltrexone Side Effects - What You Should Know

Naltrexone is a medication that is most commonly prescribed for those who are trying to manage dependence on alcohol or opioids. It is a cyclopropyl derived from oxymorphone that works as an antagonist at opioid receptor sites in the body. It blocks the effects of certain narcotics by binding to these receptors, effectively blocking the euphoric feelings typically associated with opioid use. In simpler terms, it takes the “fun” out of drug use, and is effective in helping to lower the intensity of cravings. How naltrexone works on alcoholism is not as clear, but it is believed to similarly block the effects of endorphins, reducing alcohol cravings and helping patients to abstain from drinking.

Common Forms

Naltrexone is commercially available in tablet form as a drug called ReVia or as an intramuscular injection formula known as Vivitrol and is noted for acting quickly, usually within 30 minutes with reductions in opioid cravings, noted after a couple of weeks. Naltrexone is also exported from Australia as long-acting subcutaneous implants, placed surgically.

Other Uses for Naltrexone

Low-dose naltrexone has been shown to be useful for weight loss and as relief for certain chronic pain conditions, such as fibromyalgia. Despite its effectiveness for opioid dependence and alcoholism, it is not a cure for these conditions. It is also not shown to be effective for addictions to non-opioid substances such as cocaine or quitting smoking.

Checking the Effects of Naltrexone

Naltrexone is not recommended for patients dealing with acute hepatitis or liver failure. For persons who have used opioids within the past seven to ten days, the use of naltrexone may cause them to experience withdrawal symptoms.

Side Effects

The most commonly reported side effects to naltrexone are gastrointestinal-related such as abdominal cramping and diarrhea. These are comparable to some opioid withdrawal symptoms as blocking of the mu receptor has been shown to increase gastrointestinal movement. Other reported adverse effects include anxiety, arthralgia, arthritis, common cold, depression, dizziness, drowsiness, fatigue, headaches, injection site pain, joint stiffness, malaise, muscle cramps, muscle spasms, nausea, nervousness, obsessive compulsive disorder (OCD), panic attacks, post-traumatic stress disorder (PTSD), sore throat, strep throat, syncope, vomiting, tenderness and twitching, among others. Some of these side effects may go away as your body adjusts to naltrexone, but all adverse effects should be discussed with your physician.

Naltrexone Interactions

Over 300 drugs are known to interact with naltrexone, either lowering its effectiveness, affecting the time it takes to work or increasing the intensity of adverse effects.  These medications are commonly reported to interact with naltrexone:

  • Disulfiram, commonly used for treatment of alcoholism
  • Drugs that cause sedation such as anti-anxiety treatments, antidepressants, antihistamines (1st gen), and antipsychotics
  • Drugs with opioids as components such as codeine, hydrocodone, loperamide, methadone, morphine or oxycodone. This may also include certain analgesics, anti-diarrheal medications or cold and cough medicines.

Even if you’re wondering where to buy low dose naltrexone for weight loss, you should always consult your physician or pharmacist to see how it can interact with other medications and substances.

Investigating the Origins of Naltrexone

In order to better understand the origin of naltrexone as a treatment, it’s helpful to also take a look at naloxone, which is often considered to be a short-acting variant of naltrexone. Naloxone was conceived during opioid pharmacology research. It binds to the mu opioid receptors on neurons, effectively blocking the effects of the drug and reversing the effects of an overdose. In 1961, Dr. Jack Fischman and Dr. Mozez Lewenstein synthesized and patented naloxone based on studies from Endo Laboratories’ Dr. Harold Blumberg. A decade later, an intravenous form was approved by the Food and Drug Administration for reversal of drug overdose. It became a standard emergency treatment. You may have heard of NARCAN, a nasal spray form of naloxone that is commonly used to reverse the effects of an overdose, even though it is not itself a cure for a narcotics addiction.

History of Naltrexone

 Naltrexone was also first synthesized in the early 1960s at Endo Laboratories. Researchers found it to be a very powerful opioid antagonist that was long-acting and could be administered orally. This long duration of actions meant that naltrexone could be taken once a day, offering an important advantage over naloxone and other opioid antagonists. Added to the fact that no dysphoria was experienced with naltrexone, it represented a significant progress in the fight against addiction to narcotics. Naltrexone was patented in 1967 and clinical trials to investigate its effects on narcotic dependence commenced in 1973. After further collaborative research between DuPont who had acquired Endo Laboratories, and the National Institute on Drug Abuse, naltrexone was later approved by the FDA in 1984. This oral treatment for opioid dependence was originally sold as Trexan, which was renamed as ReVia in 1995. The intramuscular injection version, Vivitrol, was approved for alcohol and opioid dependence in 2006 and 2010, respectively.

Taking Naltrexone

Naltrexone, which shouldn’t be confused with naloxone, isn’t a cure for opioid and alcohol dependence. It’s an adjunct used to psychotherapy that should be administered as part of a well-controlled addiction treatment program. Keep these things in mind:

  • Naltrexone should only be taken after abstaining from opioids for seven to ten days.
  • Naltrexone tends to be effective when taken regularly and consistently.
  • A patient who has taken naltrexone and is completely detoxified may be more susceptible to narcotics.
  • Take naltrexone as directed by your physician. Overdosing on naltrexone may result in liver injury.
  • Naltrexone is not suitable as a sole treatment for dependence on narcotics or alcohol
  • Do not take opioids while taking naltrexone. Taking large doses of opioids to work around the blocking effect may result in a coma or death.
  • Stop taking naltrexone and notify your doctor right away if you experience a yellowing of your eyes, white feces, dark urine or stomach pains that last for more than a few days.
  • Do not drink alcohol or use recreational drugs while taking naltrexone.
  • Unlike naloxone, naltrexone is not an emergency treatment for a narcotics overdose.
  • Naltrexone is not considered a substance to be abused. It has not been shown to create a physical or psychological dependence.

Dosage and Effectiveness

Within an hour of taking naltrexone orally, your body is expected to experience the peak plasma levels of naltrexone and its active metabolite, 6β-naltrexol. How long it lasts will largely depend on the dosage. Research has shown that 50 mg of naltrexone can block the effects of 25 mg of heroin taken by injection for up to 24 hours. The duration of naltrexone’s effect appears to be directly proportional to the dosage.

Other Things to Know

 Naltrexone is available in a generic formula. Although chiefly used for chemical dependency, it is sometimes prescribed for other conditions:

  • Dissociative symptoms, including depersonalization and derealization
  • Prevention of self-injury in patients with certain development disabilities, such as autism
  • Impulse control disorders such as compulsive gambling and kleptomania
  • Suppression of adverse effects associated with interferon alpha therapy.

Naltrexone shows promise as treatment for many conditions that stem from antagonizing receptor activities. As with many medicines, you should consult your physician for guidance, even if you’re using a low-dose version for weight loss or pain management. Potential interactions with other medications may negatively impact the effectiveness of naltrexone.

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This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Nu Image Medical may not offer the medications or services mentioned in this article.


About the author

Dr. Constance Odom, MD

7 min read