There is no fixed maximum duration for naltrexone treatment. The drug has been used safely for months to years in clinical settings, and many prescribers continue it as long as the patient benefits from it. For alcohol use disorder, guidelines generally recommend at least three to four months, with many patients staying on it considerably longer. For opioid use disorder, a minimum of six months is typical, and some clinicians favor open-ended treatment. The more interesting question is not how long you can be on it but what changes when you stop, because that is where the real risks emerge.
How Long People Actually Stay on It
Naltrexone is approved for two main conditions: alcohol use disorder and opioid use disorder. For alcohol, a course of at least 12 weeks is considered the minimum to see meaningful results, and research has found that some benefits from short-term treatment persist after stopping while others do not, suggesting that continued use may help certain patients maintain progress.1Archives of General Psychiatry. Six-Month Follow-up of Naltrexone and Psychotherapy for Alcohol Dependence In practice, many people with alcohol use disorder remain on naltrexone for six months to a year or longer, especially if they are doing well and tolerating it without problems.
For opioid use disorder, the extended-release injectable form (given once a month) is the more common option, and treatment courses in clinical trials usually run about six injections. A systematic review found that roughly 44% of patients completed all their scheduled injections, with adherence much higher in structured research settings than in routine care.2PubMed Central. Extended-release injectable naltrexone for opioid use disorder: A systematic review A one-year open-label extension study found that about 62% of participants who entered completed the full year, and roughly half were opioid-free at all assessments during that period.3PubMed. Injectable extended-release naltrexone (XR-NTX) for opioid dependence: long-term safety and effectiveness So while real-world adherence is a challenge, the drug itself does not become unsafe or ineffective with prolonged use.
One of the biggest practical hurdles is not biology but behavior. Dropout and non-compliance are persistent problems across both alcohol and opioid treatment. A systematic review of naltrexone for both conditions noted that despite the drug’s strong pharmacological blocking properties, treatment is frequently derailed by patients simply stopping.4ScienceDirect (Elsevier / European Neuropsychopharmacology). A systematic review of the effectiveness of naltrexone in the maintenance treatment of opioid and alcohol dependence The question for most people is less “can I take it that long” and more “will I keep taking it.”
Liver Safety Over Months and Years
Naltrexone’s original FDA labeling carried a black-box warning about liver toxicity, which has left a lasting impression on both patients and prescribers. That warning was based on early studies using very high doses, far above what is now standard. At the recommended 50 mg daily dose, the evidence is reassuring. A 12-week study in people with alcohol dependence found no elevation in liver enzymes, and levels of the two key markers actually decreased over the course of treatment.5PubMed. Study of hepatotoxicity of naltrexone in the treatment of alcoholism That downward trend makes sense: if someone is drinking less, their liver is under less strain.
More striking is what happens in people who already have liver disease, a group where you might expect the most concern. A large study of patients with and without liver disease, including some with compensated cirrhosis, found that liver enzyme levels were actually lower after naltrexone was prescribed than before, and the authors concluded the drug is safe in this population.6PubMed Central. Naltrexone for alcohol use disorder: Hepatic safety in patients with and without liver disease This does not mean the liver does not matter. Clinicians still monitor liver function periodically during treatment, especially early on or in patients with pre-existing liver conditions. But the old fear that naltrexone itself would damage the liver at therapeutic doses has not held up under scrutiny.
Other Long-Term Safety Signals
Beyond the liver, what about the rest of the body over extended use? One of the longer-running safety datasets comes from a study of patients with multiple sclerosis who took low-dose naltrexone for an extended period. Analyses comparing clinical lab values, walking ability, and brain imaging over time found no significant differences or deterioration attributable to the drug.7PubMed Central. Long-term treatment with low dose naltrexone maintains stable health in patients with multiple sclerosis In older adults, a 12-week placebo-controlled study of naltrexone for alcohol dependence found no meaningful differences in adverse effects or lab values between the drug and placebo groups.8The American Journal on Addictions. Tolerability of Naltrexone in Treating Older, Alcohol‐Dependent Patients A separate study in older patients using naltrexone for severe itching noted that side effects like insomnia and fatigue were either limited to the first two weeks or easily managed.9PubMed Central. Clinical Efficacy and Safety of Naltrexone Combination Therapy in Older Patients with Severe Pruritus
The common side effects people experience at full dose tend to cluster in the early weeks: nausea is the most frequent complaint, sometimes accompanied by headache, dizziness, or fatigue. These usually diminish with time. Naltrexone does not produce physical dependence, so when you stop taking it, there is no withdrawal syndrome and no need to taper the dose.
What Happens to Your Brain on Naltrexone
Naltrexone works by occupying opioid receptors in the brain, which blocks the rewarding effects of alcohol and opioids. When the drug sits on those receptors for weeks or months, the brain responds by increasing the number and sensitivity of its opioid receptors. Animal research has shown that total brain opioid receptors roughly doubled after about eight days of naltrexone and then leveled off, with specific increases in mu and delta receptor subtypes.10PubMed. Neurochemical and functional correlates of naltrexone-induced opiate receptor up-regulation The newly created or unmasked receptors were also more sensitive than normal, and the net effect was heightened responsiveness to opioids once the blocking drug was removed.
This receptor up-regulation has been confirmed in specific brain regions including the amygdala, thalamus, and hippocampus.11PubMed. Quantitative immunolocalization of mu opioid receptors: regulation by naltrexone This is the biological reason behind the most serious risk associated with naltrexone treatment, which is not what happens while you are on it but what happens after you stop.
The Danger Window After Stopping
When someone discontinues naltrexone after extended use, they have more opioid receptors than they started with and reduced opioid tolerance. If they then use opioids at a dose their body handled before treatment, the risk of fatal overdose spikes. Data from two clinical trials found that in the year following treatment cessation, 12 individuals died, with 10 of those deaths from accidental poisonings. The overall death rate was elevated compared to what would be expected during treatment.12PubMed. Mortality during and following treatment with extended-release naltrexone based on data from two clinical trials Patients appeared to be protected from overdose death while actively receiving the medication.
A review of adverse event reports from over 12 years of post-marketing surveillance, covering an estimated 495,000 patients who received extended-release naltrexone, found that opioid overdose reporting rates were relatively low overall but were present across all time windows after the last dose.13PubMed Central. Evaluation of Opioid Overdose Reports in Patients Treated with Extended-Release Naltrexone: Postmarketing Data from 2006 to 2018 A separate case review specifically flagged the two months after the last injection as a period of particular concern for overdose.14PubMed. Review of Case Narratives from Fatal Overdoses Associated with Injectable Naltrexone for Opioid Dependence
This is the most important thing to understand about treatment duration: stopping naltrexone is not a neutral event for someone with opioid use disorder. The decision to discontinue should involve a careful conversation with a prescriber, ideally when the person’s recovery is well-established and other supports are in place. For many patients, this is one of the strongest arguments for staying on longer.
Mood and Psychological Effects Over Time
Because naltrexone blocks opioid receptors, and the body’s natural endorphin system runs on those same receptors, some people worry about becoming emotionally flat or depressed during treatment. The evidence here is more encouraging than the worry suggests. In a study of opioid-dependent patients on either oral naltrexone or an extended-release implant, baseline levels of depression, anxiety, and anhedonia were moderately elevated but gradually fell to normal or near-normal within the first one to two months among those who stayed in treatment and avoided relapse.15PubMed Central. Anhedonia, Depression, Anxiety, and Craving for Opiates in Opiate Dependent Patients Stabilized on Oral Naltrexone or an Extended Release Naltrexone Implant
Research on the injectable form in heroin-dependent patients found that depression scores dropped significantly after just two weeks of treatment compared to baseline.16PubMed Central. Effect of extended-release naltrexone on striatal dopamine transporter availability, depression and anhedonia in heroin-dependent patients That may partly reflect the general improvement that comes with early sobriety, but it counters the narrative that naltrexone universally dulls emotional life. Some people do report feeling less pleasure from food or social activities, and those complaints deserve clinical attention. But the data do not support the idea that long-term naltrexone routinely causes worsening depression.
Low-Dose Naltrexone Is a Different Story
Low-dose naltrexone, typically in the range of 1 to 5 mg daily compared to the standard 50 mg, has become popular off-label for chronic pain conditions like fibromyalgia, inflammatory bowel disease, and multiple sclerosis.17PubMed. Low-Dose Naltrexone for Chronic Pain: Update and Systemic Review At these doses, naltrexone appears to work through a different mechanism involving anti-inflammatory effects rather than sustained opioid receptor blockade. People on low-dose naltrexone often take it indefinitely, since the conditions it treats are chronic.
The safety data at low doses is encouraging but thin. Reviews have supported the tolerability of low-dose naltrexone in multiple sclerosis, fibromyalgia, and Crohn’s disease.18PubMed. The Safety and Efficacy of Low-Dose Naltrexone in the Management of Chronic Pain and Inflammation in Multiple Sclerosis, Fibromyalgia, Crohn’s Disease, and Other Chronic Pain Disorders However, researchers have cautioned that the unique clinical effects at low doses could theoretically present new health risks that have not yet been identified, since most long-term safety data comes from the standard higher dose. No serious safety concerns have been reported to date.19PubMed Central. The use of low-dose naltrexone (LDN) as a novel anti-inflammatory treatment for chronic pain If you are on low-dose naltrexone for a chronic condition and wondering how long you can continue, the honest answer is that nobody has identified a reason to stop based on safety alone, but the long-term evidence base is not as deep as it is for the standard dose.
Surgery and Pain Management on Naltrexone
One of the most practical concerns for someone on long-term naltrexone is what happens when they need surgery or experience acute pain. Because naltrexone blocks opioid receptors, standard painkillers like morphine and oxycodone will not work as well, or at all, while the drug is active. Studies have found that naltrexone use increases the opioid doses needed for postoperative pain control, and guidelines universally recommend stopping naltrexone before planned surgery regardless of dose, indication, or route of administration.20PubMed. Treatment of Acute Pain in Patients on Naltrexone: A Narrative Review21Anesthesiology. Perioperative Naltrexone Management: A Scoping Review by the Perioperative Pain and Addiction Interdisciplinary Network
For the oral form at 50 mg, naltrexone and its active metabolite are typically cleared within about 72 hours, so stopping three days before a scheduled procedure is often sufficient. The injectable form is trickier because it releases drug continuously for about a month; if surgery is upcoming, timing the procedure toward the end of an injection cycle or delaying the next injection may be necessary. For emergencies where stopping is not an option, anesthesiologists can use non-opioid alternatives like ketamine, regional nerve blocks with local anesthetics, and other multimodal pain strategies. This is worth discussing with your prescriber well before a planned surgery, not in the pre-op room.
Pregnancy and Naltrexone
The question of how long to continue naltrexone takes on a different weight for someone who becomes pregnant or is planning a pregnancy. The human data here is limited. A case series of individuals treated with naltrexone during pregnancy for opioid or alcohol use disorder reported no fetal anomalies and one preterm delivery. None of the infants developed neonatal opioid withdrawal syndrome, which is a known complication of other addiction medications.22PubMed Central. Case series of individuals treated with naltrexone during pregnancy for opioid and/or alcohol use disorder
Animal studies, however, have raised concerns that do not map neatly onto these small human reports. Rats exposed to naltrexone during pregnancy delivered offspring that were significantly larger than controls across nearly every measure: body weight, organ weight, and body length. By weaning, the naltrexone-exposed pups were about 36% heavier than controls, with outsized increases in organs like the liver and skeletal muscle.23PubMed. Chronic exposure to the opioid antagonist naltrexone during pregnancy: maternal and offspring effects A review of both human and animal data noted that while preliminary human outcomes looked potentially favorable compared to methadone or buprenorphine, the animal findings raised enough concern that more study is needed, especially for the long-acting formulations.24PubMed Central. The effects of maternally administered methadone, buprenorphine and naltrexone on offspring: review of human and animal data For now, the decision to continue or stop naltrexone during pregnancy is highly individualized, balancing the risks of the drug against the risks of relapse to alcohol or opioid use.
Sex Differences in How the Body Responds
An underappreciated aspect of long-term naltrexone use is that men and women may respond to it differently, at least at a hormonal level. When researchers gave a single dose of naltrexone to male and female smokers, women showed a significant spike in stress hormones (ACTH and cortisol) while men did not.25PubMed Central. Acute HPA Axis Response to Naltrexone Differs in Female vs. Male Smokers This was an acute response, and whether it persists or fades with chronic use is not well established. But it hints that the endocrine consequences of long-term opioid receptor blockade might not be identical across sexes, and it is the kind of variability that clinicians are only beginning to take seriously in dosing and monitoring decisions.
Off-Label Uses and Open-Ended Treatment
Naltrexone’s reach has expanded well beyond its original FDA indications. In a study of adolescents with eating disorders, naltrexone was prescribed for an average of about 129 days. Over two-thirds showed improvement in binge eating and purging, with liver function tests remaining normal and only about 9% experiencing nausea.26PubMed Central. Naltrexone Reduces Binge Eating and Purging in Adolescents in an Eating Disorder Program That said, older reviews of opioid antagonists for eating disorders have been more cautious, noting that the published treatment studies do not yet justify routine use for conditions like bulimia or obesity.27The Journal of Clinical Pharmacology. Opiate Antagonists and Eating Behavior in Humans: A Review
What these off-label uses have in common is the absence of a clear stopping rule. When naltrexone is prescribed for a chronic condition, whether chronic pain, an eating disorder, or severe itching, the typical approach is to continue it as long as the benefit persists and side effects remain tolerable. There is no evidence that the drug accumulates in harmful ways over time or that its effectiveness wears off with extended use. Blood-level variability between individuals can be substantial, and some researchers have argued that suboptimal brain concentrations may explain why certain patients do not respond as well, rather than any inherent ceiling on how long the drug works. The question of duration, then, usually comes down to whether the condition it is treating resolves, whether the patient finds the side effects acceptable, and whether there are upcoming clinical situations like surgery or pregnancy that would require a pause.