A false positive for methamphetamine on a drug test means the test indicates the substance is present when it has not been used. This can cause serious legal or professional consequences. While drug tests are generally reliable, various factors can lead to an inaccurate initial result.
How Drug Tests Detect Substances
Initial drug screenings use immunoassay (IA) tests to quickly detect specific drug metabolites. These tests work by using antibodies that bind to the target drug or its breakdown products. Cross-reactivity is a common reason for false positives. This occurs when a substance with a similar chemical structure binds to the antibodies, leading to a positive result even if the illicit drug is absent. Immunoassay tests serve as initial screens and are not definitive, as they are sensitive but have limited specificity.
Medications Leading to False Positives
Many common medications, both prescription and over-the-counter, can trigger a false positive for methamphetamine due to similar chemical structures. Decongestants like pseudoephedrine (found in Sudafed) and ephedrine are common causes, as their structures resemble amphetamines. Phentermine, a weight-loss medication, also commonly causes false positives for amphetamines.
Certain antidepressants, particularly bupropion (Wellbutrin), are known to cause false positives for amphetamines and methamphetamines. Other antidepressants such as sertraline (Zoloft) and trazodone can also cause these results. Some antipsychotic medications like aripiprazole and chlorpromazine, as well as certain antihistamines like brompheniramine and promethazine, can similarly interfere with initial drug screens. Some antibiotics, specifically ofloxacin, can cause false positives for amphetamines or methamphetamines.
Foods and Other Substances
Beyond medications, certain foods and common products can also lead to a false positive for methamphetamine on an initial drug screen. Vicks VapoInhaler contains l-methamphetamine, a legal isomer used for nasal decongestion, but it can cause a positive result on immunoassay tests. While l-methamphetamine has little psychoactive activity, its presence can be mistaken for the illicit d-methamphetamine.
Some dietary and weight-loss supplements containing ingredients like 1,3-dimethylamylamine (DMAA) or ephedrine can also trigger false positives for amphetamines. Less common for methamphetamine specifically, other everyday items like certain energy drinks may contain stimulants that can cross-react. Substances not typically associated with illicit drug use can still lead to unexpected screening results.
Medical Conditions and Physiological Factors
Certain medical conditions and physiological states can rarely influence drug test results, leading to a false positive for methamphetamine. Conditions affecting the body’s metabolism or waste elimination processes may alter urine composition. For example, liver and kidney disease can impair the body’s ability to process and excrete substances, leading to unusual metabolic byproducts.
Diabetes, particularly when associated with diabetic ketoacidosis, has been linked to false positives for certain substances due to altered metabolic states and specific ketones. While direct evidence for methamphetamine false positives from these conditions is less frequent than with medications, these are rare instances where internal bodily processes can interfere with initial screening tests.
Confirming and Addressing a False Positive
An initial positive immunoassay screen for methamphetamine is not a definitive diagnosis of drug use. A presumptive positive result should be followed by a confirmatory test, typically Gas Chromatography-Mass Spectrometry (GC/MS). GC/MS is considered the “gold standard” in forensic drug testing due to its high specificity and accuracy, distinguishing true positives from false positives caused by cross-reactivity.
If an initial screen is positive, an individual should request a confirmatory GC/MS test. It is also important to provide a list of all medications, over-the-counter drugs, and supplements recently consumed to the testing authorities. This disclosure helps interpret the results accurately and can explain the presence of substances that caused a false positive.