How Does Naltrexone Show Up on a Drug Test?

Naltrexone is not a controlled substance and is not included on standard drug-test panels, so taking it will not produce a “positive for naltrexone” result the way using an opioid or a benzodiazepine would. The concern, though, is real for a different reason: naltrexone can trigger a false-positive result for opioids, specifically oxycodone, on the immunoassay-based urine screens used in most workplaces, clinics, and criminal-justice settings. The false positive stems from how your body breaks naltrexone down into metabolites that look enough like opioid compounds to fool the initial screening test. Understanding this quirk matters if you take naltrexone for alcohol-use disorder, opioid dependence, or any off-label purpose and face routine or random drug testing.

Why Naltrexone Can Trigger a False-Positive Opioid Result

Standard urine drug screens use a technology called immunoassay. These tests work by detecting groups of chemically similar molecules rather than identifying one exact substance. That design makes them fast and cheap, but it also means structurally related compounds can set off the same alarm. Naltrexone is an opioid antagonist, meaning it blocks opioid receptors rather than activating them. You cannot get high from it. But its chemical backbone shares enough structural similarity with opioid molecules that one of its breakdown products can cross-react with immunoassay kits designed to flag opioids.

A documented case published in The Mental Health Clinician illustrates the problem. A patient stabilized on oral naltrexone tested positive for oxycodone on a routine urine drug screen, despite not using any opioids. Confirmatory testing later identified the culprit: noroxymorphone, a lesser-known metabolite of naltrexone, had triggered the false-positive oxycodone result.¹ The patient had done nothing wrong, but the initial screen could not tell the difference between a naltrexone metabolite and the real thing.

This is not a rare conceptual risk relegated to pharmacology textbooks. If you are taking naltrexone and submit a urine sample for a workplace screening, a probation check, or a pain-management program, you could face consequences based on a result that does not reflect actual drug use. Knowing the false-positive mechanism puts you in a position to advocate for yourself before the sample is even collected.

How Your Body Breaks Down Naltrexone

When you swallow naltrexone, the drug is almost completely absorbed from the gut. Your liver then converts most of it into metabolites, the most abundant being 6-beta-naltrexol and conjugated forms of naltrexone itself. Smaller quantities of a compound called 2-hydroxy-3-O-methyl-6-beta-naltrexol also appear. About 60 percent of a dose is recovered in the urine within 48 to 72 hours.² Among those metabolites, 6-beta-naltrexol is considered pharmacologically active, meaning it also blocks opioid receptors.

Interestingly, the balance between naltrexone and 6-beta-naltrexol in your bloodstream varies from person to person. A study of heroin-dependent adults given 100 mg of oral naltrexone found that in most patients, blood levels of 6-beta-naltrexol were actually higher than those of the parent drug, though three out of thirteen patients showed the reverse pattern.³ This individual variability in metabolism likely affects how much of each metabolite ends up in urine, and by extension, how likely an immunoassay is to flag a false positive. Someone who produces more noroxymorphone relative to other metabolites may be at higher risk of triggering a positive opioid screen.

Confirmatory Testing Clears Things Up

The good news is that the false-positive problem has a straightforward technical solution. When an immunoassay flags a sample as positive for an opioid, the next step should always be a confirmatory test using a more precise technique, typically liquid chromatography-mass spectrometry or gas chromatography-mass spectrometry. These methods identify exact molecules, not families of similar ones. A confirmatory test can distinguish noroxymorphone from oxycodone, noroxycodone, or oxymorphone with high specificity.

In the published case from The Mental Health Clinician, the confirmatory analysis found no oxycodone and none of oxycodone’s primary metabolites in the sample. What it did find was noroxymorphone, which had set off the immunoassay alarm but which clearly came from naltrexone metabolism, not opioid use.¹ The patient was vindicated, but only because someone ordered the follow-up test.

The practical risk sits in that gap between the initial screen and the confirmatory test. Not every testing program automatically runs confirmatory analysis on a positive result. Workplace tests mandated by the Department of Transportation, for example, require a medical review officer to evaluate positive screens before a final determination, which provides a natural check. But many employer-driven or court-ordered programs have less rigorous review processes. If you know you take naltrexone and are subject to drug testing, proactively disclosing the medication to the medical review officer, your prescriber, or whoever interprets the results can prevent a false-positive from snowballing into real-world consequences.

What to Do Before and After a Drug Test

If you are prescribed naltrexone and anticipate a drug test, taking a few steps ahead of time can spare you a lot of stress:

Disclose the medication: Tell the testing authority, the medical review officer, or your employer’s occupational health contact that you take naltrexone before the sample is collected. Many testing protocols include a step where the donor lists current medications.
Carry documentation: A prescription label or a letter from your prescriber confirms you are taking naltrexone legitimately. This is especially helpful in criminal-justice settings where a positive opioid screen may have immediate consequences like a probation violation.
Request confirmatory testing: If an immunoassay comes back positive for opioids and you have not used any, insist on a confirmatory test. You have the right to request one in most regulated testing programs.
Contact your prescriber: Your doctor or prescriber’s office can communicate directly with the testing lab or the reviewing officer to explain the pharmacological basis for the false positive.

None of these steps guarantees a smooth experience, but they establish a clear record. A false-positive opioid result can damage trust in a treatment relationship, trigger legal action, or lead to job loss, so getting ahead of it is worth the effort.

Extended-Release Naltrexone and How Long It Stays in Your System

Oral naltrexone is typically taken daily, and as noted earlier, about 60 percent of each dose clears through the urine within two to three days. But naltrexone also comes in an extended-release injectable form, commonly known by the brand name Vivitrol, which is administered once a month. This formulation slowly releases naltrexone from a depot injected into muscle tissue, maintaining opioid blockade for roughly 30 days.⁴

The extended-release formulation means naltrexone and its metabolites, including 6-beta-naltrexol and potentially noroxymorphone, are present in your body for weeks rather than days. If you receive a monthly injection and are drug-tested at any point during that window, the false-positive risk persists throughout. You cannot simply skip a dose or time your test around a gap the way someone on daily oral tablets might think to do (not that timing games are advisable). For people on extended-release naltrexone, consistent disclosure of the medication to every entity that might test them is even more important because there is no “clean” window between doses.

When Clinicians Test FOR Naltrexone on Purpose

While standard drug panels do not look for naltrexone, there are situations where labs intentionally test for it and its metabolites. The most common reason is medication compliance monitoring. Clinicians prescribing naltrexone for alcohol-use disorder or opioid dependence sometimes need to verify that their patient is actually taking the medication, especially in criminal-justice or supervised treatment settings.

For this purpose, specialized laboratory methods have been developed that measure naltrexone and 6-beta-naltrexol directly in urine, often alongside other compounds relevant to the same patient population. One validated method uses liquid chromatography-tandem mass spectrometry to simultaneously detect ethyl glucuronide (a biomarker that indicates recent alcohol consumption), acamprosate (another alcohol-dependence medication), naltrexone, and 6-beta-naltrexol in urine samples from probationers with alcohol-use disorder.⁵ A similar approach has been developed to detect naltrexone, 6-beta-naltrexol, and ethyl glucuronide simultaneously for alcohol-abuse monitoring.⁶

These compliance-oriented tests are conceptually different from the drug screens most people worry about. They are ordered by treatment providers, not employers, and the goal is to confirm that you are taking your medication, not to catch you using a prohibited substance. If your prescriber mentions they plan to check your naltrexone levels, that is an adherence check and is nothing to be concerned about.

Does Low-Dose Naltrexone Carry the Same Risk?

Low-dose naltrexone, often abbreviated LDN, refers to naltrexone taken at doses far below the standard 50 mg used for addiction treatment, typically in the range of 1 to 5 mg. LDN has become popular for off-label uses including chronic pain, autoimmune conditions, and certain inflammatory disorders, though it remains somewhat controversial in mainstream medicine because large-scale clinical trial evidence is limited.

The metabolic pathways are the same regardless of dose. Your liver breaks LDN down the same way it breaks down a full 50 mg tablet, producing the same metabolites, including noroxymorphone. The question is whether the much smaller dose produces enough of these metabolites to trigger a false positive on an immunoassay. Immunoassay tests have detection thresholds. A full therapeutic dose of naltrexone produces substantially more metabolite than a low dose, so the false-positive risk is logically lower with LDN. But “lower” does not mean “zero.” No published studies have specifically tested LDN’s cross-reactivity rate on standard immunoassay panels, so anyone taking LDN who faces drug testing should follow the same precautions: disclose the medication, carry documentation, and be prepared to request confirmatory testing if a screen comes back positive for opioids.

Common Misconceptions About Naltrexone and Drug Tests

A few myths circulate online that are worth correcting. The first is that naltrexone will show up as an opioid on every drug test. It will not. Many people taking naltrexone never trigger a false positive. Cross-reactivity depends on the specific immunoassay kit the lab uses, the patient’s individual metabolism, and the dose. Some immunoassay platforms are more prone to cross-reactivity with structurally related compounds than others.

The second misconception is that naltrexone is “just like taking an opioid” in terms of drug-test implications. Naltrexone is pharmacologically the opposite of an opioid. It blocks the receptors that opioids activate. The false-positive issue is purely a technical limitation of the screening technology, not a reflection of any similarity in how these drugs affect the brain or body.

A third myth is that you should stop taking naltrexone before a drug test to avoid a false positive. If you are taking naltrexone for opioid dependence, stopping it to avoid a drug screen defeats the purpose of the medication and puts you at risk for relapse. For people in recovery, maintaining the medication and simply documenting it for the testing authority is far safer than interrupting treatment. The same logic applies to people taking naltrexone for alcohol-use disorder or any other indication.

Naltrexone Versus Naloxone on Drug Screens

People sometimes confuse naltrexone with naloxone, which is the active ingredient in the rescue medication used for opioid overdose reversals. Both are opioid antagonists. Both block opioid receptors. And both share structural features with opioid molecules that could theoretically cause immunoassay cross-reactivity. However, their clinical contexts and detection windows are quite different.

Naloxone is typically administered as a one-time emergency injection or nasal spray. It is metabolized rapidly, with a much shorter duration of action than naltrexone. Unless you are tested very shortly after receiving naloxone, it is unlikely to produce a positive drug screen. Naltrexone, by contrast, is taken on an ongoing basis, either daily or monthly, so its metabolites are continuously present in your urine at higher concentrations over a longer period. The sustained presence of naltrexone metabolites is what makes the false-positive scenario more clinically relevant for naltrexone than for naloxone.

Neither drug is a controlled substance, and neither is targeted by standard drug panels. The distinction matters because patients are sometimes told generically that “opioid antagonists can cause false positives on drug tests,” which is technically true of both but practically much more of a concern for people on ongoing naltrexone therapy.

The Role of Drug Testing in Naltrexone-Based Treatment Programs

Drug testing plays a somewhat paradoxical role in treatment programs that prescribe naltrexone. On one hand, urine drug screens are used to verify that a patient is not using illicit opioids while on naltrexone treatment. On the other hand, naltrexone itself can confuse those very tests. Clinicians managing patients on naltrexone need to be aware of this interaction and interpret positive opioid screens with appropriate skepticism rather than assuming a relapse.

Research on naltrexone-based treatment programs has explored how opioid-positive urine results relate to treatment retention. In a study comparing different doses of naltrexone to placebo, opiate-positive urines predicted treatment dropout for patients on placebo or low-dose naltrexone, but less so for those on higher doses, where a positive urine was more often followed by sustained abstinence rather than dropout.⁷ The implication is that at effective doses, naltrexone’s blockade may reduce the reinforcing effects of opioid use even when use occurs, which complicates the interpretation of positive urine results even further. A positive screen in a patient on adequate naltrexone might reflect the naltrexone metabolite cross-reactivity described earlier, brief opioid exposure that was pharmacologically blocked, or a combination of both.

Clinicians working in addiction medicine are increasingly aware of the false-positive issue, but the awareness is far from universal. Pain-management programs, employee-assistance programs, and court-supervised testing programs may not have staff trained to recognize this specific interaction. If you are in treatment and receive an unexpected positive opioid result, bringing the published evidence on naltrexone-related false positives to the attention of your treatment team or reviewing officer is entirely reasonable and can be supported by your prescriber.

Hair and Blood Tests

Most of the discussion around naltrexone and drug testing focuses on urine, because urine immunoassay is by far the most common format. But drug tests can also be performed on hair, blood, or oral fluid. Hair tests detect drug metabolites incorporated into the hair shaft over weeks to months. Because naltrexone is not a substance that standard hair panels screen for, it will not appear on a hair drug test. The question of whether naltrexone metabolites could cross-react with opioid-targeted hair assays is less studied than the urine scenario, though hair testing generally uses different detection chemistry and the cross-reactivity profiles do not translate directly.

Blood tests used in clinical settings can detect naltrexone and 6-beta-naltrexol directly when the goal is therapeutic monitoring, but blood is rarely used for routine workplace or legal drug screening. Oral-fluid tests, which are growing in popularity for roadside and workplace screening, carry the same theoretical cross-reactivity risk as urine immunoassays because they use similar antibody-based detection. If you face an oral-fluid drug test while on naltrexone, the same advice applies: disclose the medication and request confirmatory analysis if the initial screen is positive.