The abbreviation ng/mL stands for nanograms per milliliter, a unit of concentration that tells you how much of a substance is dissolved in a given volume of liquid. On a drug test, it measures how many billionths of a gram of a drug or its metabolite are present in each milliliter of your sample, whether that sample is urine, blood, or saliva. A nanogram is incredibly small, and these trace-level measurements are what allow labs to detect drug use days or even weeks after your last exposure. But what matters most on your test result is not the raw number itself; it is whether that number falls above or below a predetermined threshold called the cutoff.
How Cutoff Concentrations Decide Your Result
A drug test does not simply report “drugs found” or “drugs not found.” Instead, every test has a specific cutoff concentration, expressed in ng/mL, that separates a positive result from a negative one. If the concentration of a drug or metabolite in your sample meets or exceeds the cutoff, the result is positive. If it falls below, the result is negative, even if a tiny amount of the substance is technically present. This is a deliberate design choice: setting a floor prevents trace-level contamination or incidental exposure from triggering a positive result for everyone who walks through the door.
The cutoff you face depends on which drug is being tested, what type of specimen is collected, and who set the testing rules. Federal workplace testing in the United States follows guidelines established by the Substance Abuse and Mental Health Services Administration (SAMHSA), while clinical pain management programs, courts, and private employers sometimes use different thresholds. For marijuana, the standard federal urine screening cutoff is 50 ng/mL for the THC metabolite (THC-COOH), with a confirmatory cutoff of 15 ng/mL.1Clinical Chemistry. Lowering cutoffs for initial and confirmation testing for cocaine and marijuana: large-scale study of effects on the rates of drug-positive results For cocaine metabolites, the standard screening cutoff is 300 ng/mL with a 150 ng/mL confirmation threshold, though SAMHSA later lowered that confirmation cutoff to 100 ng/mL.2Clinica Chimica Acta. Determination of illicit drug cutoff values in a pain patient population
Oral fluid testing uses much lower cutoffs because drugs are present in saliva at lower concentrations than in urine. For cannabis, an oral fluid screening cutoff might be as low as 1 ng/mL for THC, with confirmation at 0.5 ng/mL.3Journal of Analytical Toxicology. Detection of Marijuana Use by Oral Fluid and Urine Analysis Following Single-Dose Administration of Smoked and Oral Marijuana Meanwhile, the Australian/New Zealand standard uses a THC oral fluid cutoff of 10 ng/mL and sets oral fluid cutoffs for morphine and codeine at 25 ng/mL each, far below the urine thresholds for the same substances.4PubMed Central. Comparison of Urine and Oral Fluid for Workplace Drug Testing
Screening Versus Confirmation and Why There Are Two Numbers
Most drug testing follows a two-step process, and each step has its own cutoff. The initial screening test, usually an immunoassay, is fast and inexpensive but somewhat imprecise. It uses antibodies that react to a class of drugs rather than identifying one specific molecule. If the screening result lands at or above the cutoff, the sample moves to a confirmation test, which uses a more specific technique like gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). The confirmation cutoff is typically lower than the screening cutoff because the method is precise enough to identify the exact substance at smaller concentrations.
This two-tier system exists because immunoassays can produce both false positives and false negatives. A study comparing immunoassay screening with LC-MS/MS confirmation in people under probation monitoring found that agreement between the two methods varied widely depending on the drug class. Buprenorphine results showed moderate agreement, amphetamines somewhat less, and opioids showed very poor agreement. For cannabinoids and benzodiazepines, the two methods barely agreed at all when results hovered near the cutoff.5PubMed Central. Comparison of Immunoassay Results near Cutoff Values with LC-MS/MS in Individuals with Substance Use Disorder Under Probation That study underscored something toxicologists already knew: a screening result near the cutoff line is unreliable on its own. Confirmation testing catches mistakes in both directions.
For opioid screening specifically, validation work on one commonly used immunoassay for hydrocodone showed sensitivity of about 90% at a 100 ng/mL cutoff. One specimen containing 110 ng/mL of hydrocodone was missed entirely by the screening assay because the semi-quantitative reading came in just below the threshold.6PubMed. Suitability of the DRI Hydrocodone/Hydromorphone Immunoassay in the Clinical Environment at a Lower Cutoff: Validation With LC-MS/MS Analysis A person who genuinely used a drug could test negative on a screening immunoassay, which is exactly why clinical labs run confirmation when results are close to the line.
Common Drug Cutoff Levels in Urine
Because cutoff levels differ by drug class and testing context, it helps to know the general ranges. Federal workplace urine testing guidelines, which many employers adopt, set the following screening and confirmation cutoffs:
- Marijuana (THC-COOH): 50 ng/mL screening, 15 ng/mL confirmation
- Cocaine (benzoylecgonine): 150 ng/mL screening, 100 ng/mL confirmation (lowered from 300/150 under revised SAMHSA rules)
- Opiates (morphine, codeine): 2,000 ng/mL screening, 2,000 ng/mL confirmation
- Amphetamines/methamphetamine: 500 ng/mL screening, 250 ng/mL confirmation (lowered from 1,000/500)
The opiate cutoff has a specific backstory. Labs originally used a 300 ng/mL cutoff for morphine and codeine, but that level caught too many people who had eaten poppy-seed bagels or taken small therapeutic doses of codeine. The cutoff was raised to 2,000 ng/mL specifically to reduce those false positives.7PubMed. Experience with a urine opiate screening and confirmation cutoff of 2000 ng/mL That is a dramatic jump, and it illustrates an important tension: lower cutoffs catch more genuine drug use but also flag more innocent exposures, while higher cutoffs reduce false positives but let some real use slip through. Research on clinical populations has supported lowering cutoffs for methamphetamine and cocaine metabolites to better identify users, while the THC-COOH confirmation cutoff has stayed at 15 ng/mL.2Clinica Chimica Acta. Determination of illicit drug cutoff values in a pain patient population
How Long Drugs Stay Above the Cutoff
The ng/mL number on a drug test reflects how much metabolite your body has excreted into your specimen at that moment. For most drugs of abuse, oral fluid detection windows are short, typically 12 to 48 hours after use, though methamphetamine has been detected in saliva for up to 72 hours after multiple doses, and cocaine has been found for as long as 9 days in chronic users.4PubMed Central. Comparison of Urine and Oral Fluid for Workplace Drug Testing The general hierarchy of detection windows, from longest to shortest, is hair, then urine, then sweat, then oral fluid, then blood.
Cannabis is a special case because THC is fat-soluble. Heavy users can store significant amounts in body fat, which slowly releases THC-COOH into the urine over weeks. In one study, urinary THC-COOH concentrations exceeded 1,000 ng/mL in some heavy users more than five days after their last use.8Forensic Science International. Residual cannabis levels in blood, urine and oral fluid following heavy cannabis use A study of adolescent and young adult cannabis users tracked elimination during verified abstinence and found a median detection window of about 10 days, but with an estimated range stretching from 4 to 80 days. After more than 25 days of abstinence, 40% of participants still had detectable THC-COOH above 5 ng/mL, and about one in five still produced a result that would count as positive under federal guidelines (above 50 ng/mL on screening, above 15 ng/mL on confirmation).9PubMed Central. Urinary 11-nor-9-carboxy-tetrahydrocannabinol elimination in adolescent and young adult cannabis users during one month of sustained and biochemically-verified abstinence This means a heavy user who has genuinely stopped can continue testing positive for well over a month.
When Hydration Changes the Number
Because urine drug concentrations are measured per milliliter of fluid, how dilute or concentrated your urine is at the time of collection directly affects the ng/mL reading. Drinking large amounts of water before a test can push drug metabolite levels below the cutoff, creating a false-negative result.10Journal of Analytical Toxicology. Normalization of Urinary Drug Concentrations with Specific Gravity and Creatinine This is one of the most common ways people attempt to manipulate urine drug tests.
Labs counter this by measuring creatinine concentration and specific gravity alongside the drug assay. Creatinine is a waste product your muscles produce at a fairly steady rate. A very low creatinine level signals that the sample is diluted beyond what normal hydration would produce. Some labs then normalize the drug concentration by adjusting the ng/mL value relative to the creatinine level, which can flip a below-cutoff result back to a positive one.11PubMed. The impact of creatinine reference value: Normalization of urinary drug concentrations Research on normalization techniques has found that specific-gravity-adjusted creatinine normalization and creatinine regression methods provide the most reliable correction, though the timing of sample collection also matters: spot-urine samples collected between roughly 2 p.m. and 2 a.m. tend to give results most consistent with 24-hour averages.12Journal of Pharmaceutical and Biomedical Analysis. Effect of creatinine and specific gravity normalization techniques on xenobiotic biomarkers in smokers’ spot and 24-h urines
Beyond dilution, some people add chemicals directly to the sample to interfere with the assay. Oxidizing adulterants in particular can degrade drug metabolites and produce false negatives.13PubMed. Bioanalysis of urine samples after manipulation by oxidizing chemicals: technical considerations Labs test for common adulterants as part of specimen validity checks, but the arms race between tampering methods and detection methods is ongoing.
Secondhand Cannabis Smoke and Passive Exposure
One of the most common questions about ng/mL cutoffs is whether you can fail a drug test from being in the same room as someone who is smoking marijuana. The answer is: it depends on the cutoff, the ventilation, and how extreme the exposure was. In a controlled study, non-smokers sat in an unventilated room with smokers for an hour. Their maximum urinary THC-COOH concentrations ranged from about 1.3 to 57.5 ng/mL by GC-MS. At the standard federal screening cutoff of 50 ng/mL, only one specimen tested positive. At a lower 20 ng/mL cutoff, several specimens were positive.14PubMed Central. Non-Smoker Exposure to Secondhand Cannabis Smoke. I. Urine Screening and Confirmation Results
Ventilation made a major difference. When the experiment was repeated with a ventilated room, blood cannabinoid levels were much lower, and no urine specimens tested positive even at 20 ng/mL.15Drug and Alcohol Dependence. Non-smoker exposure to secondhand cannabis smoke II: Effect of room ventilation on the physiological, subjective, and behavioral/cognitive effects For oral fluid tests, passive exposure can produce positive results, but the window appears limited to roughly 30 minutes after exposure ends, with THC concentrations in passive subjects’ saliva ranging from about 1 to 26 ng/mL during that brief period.16PubMed. Passive cannabis smoke exposure and oral fluid testing
In practical terms, casual contact with cannabis smoke in a well-ventilated setting is very unlikely to push you above the 50 ng/mL federal urine cutoff. But sitting in a hotboxed car or a small, sealed room with active smokers is a different story, especially if the test uses a lower cutoff. Knowing the ng/mL threshold that applies to your particular test matters for understanding your actual risk.
Why a Positive Number Does Not Mean You Are Impaired
Perhaps the biggest misconception about ng/mL values on a drug test is that a higher number means a person is more intoxicated, or that any positive result indicates current impairment. Neither is true. A workplace cannabinoid test, for instance, detects a metabolite (THC-COOH) that your body produces after it processes THC. This metabolite has no psychoactive effect, and its presence in urine says nothing about whether you are high at the time of the test. A positive result does not document impairment or even necessarily recent use.17PubMed Central. Interpretation of Workplace Tests for Cannabinoids
Research on cannabis and cognitive performance has reinforced this disconnect. A study that tested THC, cannabidiol, and cannabinol levels in blood, urine, and oral fluid found that none of those levels correlated with actual cognitive or psychomotor impairment after either oral or vaporized cannabis use.18National Institute of Justice. Field Sobriety Tests and THC Levels Unreliable Indicators of Marijuana Intoxication You could have a high ng/mL reading and be completely sober because your body is still clearing stored metabolites, or you could have a relatively low reading shortly after use before metabolite levels have peaked. The ng/mL number tells you about the chemistry of the specimen, not the state of the person.
This distinction matters in legal, employment, and medical settings. An employee who tests positive on a Monday for cannabis they used the previous Saturday is not impaired at work, yet the ng/mL reading treats their sample the same as someone who smoked an hour ago. Courts and policymakers are increasingly wrestling with this gap between detection and impairment, but for now, the cutoff system does not try to distinguish the two. Understanding what ng/mL actually measures helps you understand the limits of what a test result can and cannot tell anyone about you.
False Positives From Medications and Other Substances
Because immunoassay screening tests react to a family of chemical structures rather than one precise molecule, cross-reactivity is a persistent problem. Certain over-the-counter and prescription drugs share enough structural similarity with illicit substances to trigger a positive screening result. Common examples include some antihistamines and sleep aids cross-reacting with amphetamine assays, proton pump inhibitors triggering THC screens, and quinolone antibiotics producing false positives for opiate assays. Immunoassays are broadly recognized as prone to both false-positive and false-negative results, which is exactly why confirmation testing exists.19PubMed Central. Buyer Beware: Pitfalls in Toxicology Laboratory Testing
If you are taking any medication and are facing a drug test, disclosing your prescriptions to the medical review officer (MRO) before or at the time of the test is the most reliable way to protect yourself. The MRO’s job is to evaluate a positive result in the context of your medical history and determine whether a legitimate prescription explains it. A confirmation test using LC-MS/MS can distinguish the exact molecule present, separating a prescription amphetamine like Adderall from illicit methamphetamine, or a prescribed benzodiazepine from an unprescribed one. The ng/mL reading on a screening test alone cannot make that distinction.
How the Same Drug Gets Different Cutoffs in Different Contexts
You might encounter wildly different cutoff numbers depending on who ordered the test and why. Federal workplace programs follow SAMHSA guidelines, but clinical pain management programs sometimes use much lower cutoffs to verify that patients are actually taking their prescribed medications rather than diverting them. Research on clinical populations has suggested that cutoffs as low as 10 ng/mL for THC-COOH and 30 ng/mL for cocaine metabolite would catch the vast majority of users in a pain-management population.2Clinica Chimica Acta. Determination of illicit drug cutoff values in a pain patient population That 10 ng/mL THC-COOH cutoff is far stricter than the 50 ng/mL used in workplace screening; it would flag many more people, including those with older or lighter exposure.
Drug courts, probation programs, and military testing also set their own thresholds. Some programs use a 20 ng/mL screening cutoff for cannabis, which dramatically changes who tests positive. As the secondhand smoke research showed, the difference between a 50 ng/mL and a 20 ng/mL cutoff can be the difference between negative and positive for someone who was merely in the room. When you receive a drug test result, the specific cutoff applied is as important as the ng/mL number itself. A “negative” under one program’s rules could be a “positive” under another’s.
For oral fluid testing, cutoffs tend to run an order of magnitude lower than urine cutoffs because drug concentrations in saliva are naturally lower. Urine screening for opiates at 2,000 ng/mL versus oral fluid screening for morphine at 25 ng/mL reflects the biology of how drugs partition into different body fluids, not a difference in sensitivity philosophy.4PubMed Central. Comparison of Urine and Oral Fluid for Workplace Drug Testing This is why comparing ng/mL values across specimen types is meaningless. A urine THC-COOH concentration of 30 ng/mL and a blood THC concentration of 5 ng/mL are measuring entirely different molecules in different fluids at different time points after use. Neither number translates directly into the other.