Drug tests are common in employment and medical evaluations. A “false positive” occurs when a test indicates a substance was used, but it wasn’t, or not due to illicit drug use. This can have serious consequences, including legal issues, job loss, or unnecessary medical interventions. Understanding the factors that can lead to a false positive for amphetamines is important for anyone undergoing such testing.
Over-the-Counter Culprits
Many commonly available over-the-counter (OTC) medications can trigger a false positive for amphetamines on a drug test. This often happens because these substances share chemical structures similar to amphetamines, leading to cross-reactivity with initial immunoassay screenings. Decongestants containing pseudoephedrine, found in products like Sudafed, are well-known culprits due to their structural resemblance. Ephedrine, present in some asthma medications and dietary supplements, can also cause false positives.
Other OTC medications that may interfere include phenylephrine, another common nasal decongestant. While less common, antihistamines like diphenhydramine (e.g., Benadryl) and brompheniramine have also been implicated in causing false-positive urine amphetamine results.
Prescription Medications That Interfere
A range of prescription medications can also lead to false positive amphetamine results, primarily due to structural similarities or metabolic pathways that mimic amphetamine compounds. Antidepressants are a notable category, with bupropion (Wellbutrin) being a frequent cause of false positives for amphetamines or methamphetamines. Bupropion metabolites can cross-react with screening tests, with false positives occurring when metabolite concentrations exceed 500 ng/mL. Other antidepressants like fluoxetine (Prozac) and trazodone have also been linked to false positive amphetamine results.
Certain blood pressure medications, such as labetalol, can trigger false positives, as its metabolite is structurally similar to amphetamine. Metformin, a medication for diabetes, has been reported in rare cases to cause false positives, particularly with immunoassay tests. Antipsychotic medications like chlorpromazine and promethazine, and some quinolone antibiotics such as ofloxacin, can also cause false-positive amphetamine results.
Food, Supplements, and Other Ingestibles
Beyond medications, certain foods, supplements, and other ingested substances can occasionally lead to false positive amphetamine drug tests. The principle of food interference, often associated with opiates, can extend to amphetamines. Some herbal supplements contain compounds that can mimic stimulants or interfere with test reagents; ginseng, for example, has been linked to false positives.
Products containing ephedra-like compounds, found in energy drinks or weight-loss supplements, can produce similar results due to their chemical structure. Even trace amounts of amphetamine-like compounds in unregulated supplements or cross-contamination during manufacturing can contribute. Certain dietary items can lead to unexpected drug test results if their metabolites cross-react with screening assays.
Physiological Factors and Testing Protocol Issues
Internal bodily conditions and errors within the testing process itself can also contribute to false positive amphetamine results. Certain physiological states can alter metabolism or introduce interfering substances into urine. For example, kidney disease or liver dysfunction can impact how the body processes various compounds, potentially leading to an accumulation of substances that cross-react with drug tests. Diabetes, particularly in cases of ketoacidosis, can produce ketones that might interfere with some immunoassay screenings.
Issues with testing protocols, from sample collection to laboratory analysis, can also cause inaccurate results. Improper sample handling or storage, such as bacterial contamination, can degrade a sample or introduce compounds that interfere with the test. Laboratory errors, including cross-contamination of samples or incorrect calibration of testing equipment, represent direct issues with the analysis process. These procedural flaws can lead to a preliminary positive result even when no amphetamines are present.
Confirming an Initial Positive Result
An initial positive result for amphetamines from a screening test, typically an immunoassay, does not necessarily mean illicit use has occurred. These initial tests are designed to be highly sensitive but can sometimes lack specificity, leading to false positives. Therefore, a positive screening result requires confirmatory testing to ensure accuracy.
The standard for confirming an initial positive result involves more sophisticated analytical techniques such as Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Mass Spectrometry (LC-MS). These methods are highly accurate and can precisely identify and quantify specific compounds, distinguishing true amphetamines from other substances that might cause cross-reactivity. Individuals facing a preliminary positive result should immediately inform the testing facility or relevant authority about all medications, supplements, and even certain foods they have recently consumed. Providing a comprehensive list of ingested substances aids in the interpretation of results and helps to avoid unwarranted consequences.