What Does MET Mean on a Drug Screen?

MET is the abbreviation for methamphetamine on a urine drug screen. When you see “MET” listed on a drug test panel or results sheet, it refers specifically to the methamphetamine assay, which is one of the standard drug classes tested for in workplace, clinical, and forensic settings. A positive MET result does not automatically mean someone used illicit methamphetamine, though. The initial screening test is designed to cast a wide net, and a surprising number of common medications can trigger it.

What a MET Panel Actually Tests For

Drug screens come in different configurations, often labeled by the number of substances they cover: a 5-panel, 10-panel, or 12-panel test. The MET line on these panels uses immunoassay technology, which works by detecting whether molecules in the urine sample are structurally similar enough to methamphetamine to bind with specific antibodies. If enough binding occurs, the test reads as positive.

The problem is that immunoassay tests are not very selective. They react to the general shape of the methamphetamine molecule, not its exact identity. This means they can flag a variety of compounds that share a similar chemical backbone, including prescription medications and over-the-counter products that have nothing to do with illicit drug use. A review of commonly prescribed medications found that false-positive results for amphetamine and methamphetamine were the most commonly reported among all drug classes tested by immunoassay.¹

In one study that evaluated how immunoassay results held up against confirmatory testing, over half of the samples that initially screened positive for amphetamines turned out to be negative when subjected to more precise laboratory analysis.² That is a strikingly high false-positive rate, and it underscores why a positive MET screen is never the final word.

Medications and Substances That Can Trigger a False Positive

If you have tested positive on a MET screen and know you have not used methamphetamine, the most likely explanation is cross-reactivity from something else you took. The list of potential culprits is longer than most people expect. Research has identified a range of prescription and over-the-counter medications that can cause false-positive results on amphetamine and methamphetamine immunoassays, including ephedrine, pseudoephedrine, labetalol, metoprolol, certain antidepressants, metformin, ranitidine, ofloxacin, and selegiline.³

Nasal decongestants deserve special attention here. Products containing pseudoephedrine (sold as Sudafed and its generics) are among the most common causes of false positives on MET panels. Vicks inhalers, which contain levomethamphetamine (a form of methamphetamine that is legal and sold over the counter), are another well-known trigger.⁴ An evaluation of eight commercial methamphetamine test kits found that ephedrine and pseudoephedrine caused significant interference on most kits, with some kits producing false positives at concentrations as low as 1 mg/L.⁵

Not all test kits perform equally. That same evaluation found wide variation in specificity across brands: some kits were far more prone to false positives than others when exposed to common cold-syrup ingredients like brompheniramine, phenylpropanolamine, and methylephedrine.⁵ Point-of-care cup tests used in clinics and urgent care settings have also been shown to produce false positives for methamphetamine when compared against laboratory mass spectrometry results.⁶

What Happens After a Positive MET Screen

A positive immunoassay result for MET is considered “presumptive positive.” In any setting with consequences attached to the result (employment, legal proceedings, pain management programs), the next step is confirmation testing using a much more precise technique. The standard methods are gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–tandem mass spectrometry (LC-MS/MS). These instruments separate and identify individual compounds by their exact molecular weight and fragmentation pattern, rather than relying on structural similarity the way immunoassays do.

LC-MS/MS has been authorized for use in federally regulated workplace drug testing programs since 2008 and has been shown to produce results at least as valid as GC-MS across a range of drug analytes including amphetamine and methamphetamine.⁷ Modern confirmation methods can quantify both amphetamine and methamphetamine in a single run alongside other drug classes.⁸

Confirmation testing does not just say “positive” or “negative.” It provides a quantitative measurement of how much methamphetamine and amphetamine are present. That matters because methamphetamine is metabolized in the body into amphetamine. After someone uses methamphetamine, their urine will contain both compounds. One study of controlled methamphetamine administration found that the ratio of amphetamine to methamphetamine in urine increased over time, from roughly 13% soon after use to about 36% in later specimens.⁹ Laboratories can use this ratio to help determine whether methamphetamine was the original substance consumed, or whether the methamphetamine detected might have come from a different source.

The D-Meth Versus L-Meth Distinction

This is where things get particularly nuanced, and it is one of the least understood aspects of MET drug testing among the general public. Methamphetamine exists in two mirror-image forms, called enantiomers: d-methamphetamine and l-methamphetamine. The “d” form is the illicit, highly potent stimulant. The “l” form is a much weaker compound that is legally available over the counter in Vicks nasal inhalers, where it acts as a decongestant. Standard drug tests, and even standard confirmation tests, cannot tell these two forms apart.

Because of the legal availability of l-methamphetamine, forensic guidelines require that a sample contain more than 20% d-methamphetamine to be considered evidence of illicit drug use.¹⁰ Distinguishing between d- and l-methamphetamine requires specialized chiral analysis, a separate step that is not performed on routine drug screens. Chiral separation by liquid chromatography–tandem mass spectrometry has proven more reliable than traditional gas chromatography methods for this purpose.¹¹

In the chronic pain patient study mentioned earlier, 48 methamphetamine-positive samples were sent for chiral confirmation. The overwhelming majority, about 94%, were positive for d-methamphetamine (the illicit form), while roughly 6% were positive for l-methamphetamine only, consistent with over-the-counter nasal inhaler use.² Chiral analysis is the most effective tool for sorting out whether a positive result comes from a legal product or an illegal one.¹²

If you have a legitimate reason for a positive MET result (such as using a Vicks inhaler), requesting chiral testing through a medical review officer is the path to clearing your name. Not all laboratories perform this test routinely, but it can be specifically ordered.

How Long MET Stays Detectable

Detection windows for methamphetamine vary depending on the specimen type and the dose consumed. Urine is the most commonly tested matrix and has a longer detection window than oral fluid or blood. Research comparing urine, oral fluid, and plasma after controlled methamphetamine administration found that urine drug concentrations were substantially higher than those in oral fluid, and detection times for urine were generally longer than those observed for oral fluid at standard cutoff concentrations.¹³

For most people, methamphetamine is detectable in urine for roughly two to four days after a single use, though heavy or chronic use can extend that window. Oral fluid testing offers a shorter detection window, which can be either an advantage or a limitation depending on the testing context. In oral fluid, methamphetamine concentrations actually exceed those in plasma, but the detection period is still shorter than in urine.¹³ Hair testing, while not typically labeled with a “MET” abbreviation the way rapid panels are, can detect methamphetamine for months.

Individual variation in detection times is considerable. Body composition, hydration status, metabolic rate, kidney function, and urine pH all influence how quickly the drug is cleared. The urinary pharmacokinetics of methamphetamine show wide individual ranges: in one controlled-dose study, maximum excretion rates ranged from 403 to nearly 5,000 micrograms per hour, with no clear relationship between dose and excretion rate.⁹ In practical terms, two people who take the same amount of methamphetamine can show very different urine concentrations at the same time point.

Specimen Tampering and Validity Testing

Because the stakes of a positive drug test can be high, some people attempt to beat the test by tampering with their urine sample. Common strategies include diluting the sample (by drinking excessive water beforehand or adding water after collection), substituting someone else’s urine, or adding chemical adulterants to the specimen. Laboratories are well aware of these tactics and run specimen validity tests alongside the drug assay. These tests check the urine’s creatinine concentration, specific gravity, pH, temperature, and the presence of known adulterant chemicals.¹⁴

A large study in Taiwan examining over 21,000 submitted urine drug test samples found that tampering rates (including dilute, substituted, or otherwise invalid specimens) averaged about 1% in workplace settings and nearly 4% in court-ordered testing.¹⁵ The higher rate in legal contexts likely reflects the more serious consequences driving stronger motivation to cheat. Newer detection strategies are moving toward more sophisticated markers, including unique metabolite profiles and DNA methylation patterns, which would make tampering even harder to pull off.¹⁶

Newer Drugs That Slip Past the MET Panel

While the MET panel catches methamphetamine and many structurally similar compounds (sometimes too many, as the false-positive problem illustrates), it misses some newer amphetamine-like substances entirely. Synthetic stimulants known as new psychoactive substances, or “designer drugs,” are deliberately engineered to produce similar effects to methamphetamine while having just enough structural difference to evade immunoassay detection. Research has confirmed that amphetamine-like drugs capable of causing serious toxicity or impairment may not cross-react with available immunoassay kits and can therefore go entirely undetected on standard panels.¹⁷

This is something to be aware of if you are a clinician, employer, or anyone interpreting drug screen results. A negative MET screen does not rule out all stimulant use. It rules out methamphetamine and the family of compounds close enough in structure to trigger the antibody reaction. If clinical signs suggest stimulant use but the screen comes back clean, broader testing with mass spectrometry may be warranted.

MET Results in Pregnancy

Drug screening during pregnancy is routine in many hospitals, and a positive MET result during labor and delivery carries specific clinical significance beyond the legal and social implications. A study of obstetrical outcomes found that a methamphetamine-positive urine drug screen at the time of delivery was associated with a roughly five-fold increased risk of placental abruption and a three-fold increased risk of preterm birth. Neonates born to mothers who tested positive had lower Apgar scores, and perinatal mortality was about seven times higher.¹⁸ These associations underscore why hospitals screen for methamphetamine during delivery: it changes clinical management and preparedness for complications.

The same false-positive concerns apply in this context, though, which makes confirmatory testing all the more important. A laboring patient who took Sudafed for congestion and triggers a positive MET screen should not be treated the same as one who used illicit methamphetamine. The consequences of misinterpretation in a delivery room can include child protective services involvement, so accurate follow-up testing matters enormously.

What to Do If You Get an Unexpected MET Positive

If you receive a positive MET result and believe it is incorrect, the single most important thing you can do is request confirmatory testing. In workplace settings governed by federal guidelines, this is your right: the initial immunoassay screen is always followed by mass spectrometry confirmation before any adverse action is taken. A medical review officer reviews the confirmed results and can consider legitimate medical explanations such as prescribed medications or over-the-counter products.

Keep a list of everything you have taken in the past week, including cold medications, nasal inhalers, herbal supplements, and prescription drugs. Bring this to the review. If the confirmation comes back positive for methamphetamine specifically, you can request chiral testing to determine whether the methamphetamine in your sample is the d-form (illicit) or the l-form (consistent with products like Vicks inhalers). Not every situation guarantees access to all these testing tiers, particularly in emergency department or urgent care settings where point-of-care cup tests may be the only analysis performed. In those cases, advocating for proper confirmation is on you or your healthcare provider.

The underlying reality of MET drug testing is that the initial screen is a blunt instrument. It does what it is designed to do: flag samples that might contain methamphetamine for further investigation. But treating a presumptive positive MET result as proof of illicit drug use, without confirmation, is a mistake that happens far more often than it should.