Drug tests are used in various settings, from employment screenings to medical evaluations, to detect substances in a person’s system. While these tests aim for accuracy, they can sometimes produce a “false positive” result, indicating the presence of a drug like amphetamine even when the individual has not consumed it. This occurs when other substances, often with similar chemical structures, are mistakenly identified by the initial screening tests. Understanding factors that can lead to such erroneous results is important for anyone undergoing drug testing.
Prescription Medications
A common cause of false positive amphetamine results stems from various prescription medications. Certain drugs prescribed for attention-deficit hyperactivity disorder (ADHD), such as atomoxetine and methylphenidate, can trigger these false positives on initial immunoassay screens. While methylphenidate has often been cited, some research indicates it may not cause false positives for amphetamines, although stimulant treatments for ADHD can result in a positive screen for amphetamines.
Antidepressants are another class of prescription drugs known to cause false positives for amphetamines. Bupropion, an atypical antidepressant, is frequently implicated due to its structural similarity to amphetamines. Other antidepressants, including fluoxetine, sertraline, venlafaxine, and trazodone, have also been reported to cause these cross-reactions, often due to their metabolites. Additionally, some antipsychotic medications like chlorpromazine and thioridazine, along with beta-blockers such as labetalol, can lead to false positive amphetamine results.
Over-the-Counter Drugs and Dietary Supplements
Over-the-counter (OTC) medications and dietary supplements are another category of substances that can lead to false positive amphetamine test results. Nasal decongestants containing pseudoephedrine or phenylephrine are frequent culprits, as their chemical structures are similar to amphetamines. Even products like Vicks inhalers, which contain l-methamphetamine, an isomer useful for nasal congestion, can cause a false positive for amphetamines.
Certain weight-loss supplements also pose a risk for false positives. Products containing ingredients like phentermine, which is chemically similar to amphetamines, or 1,3-dimethylamylamine (DMAA), a sympathomimetic found in some supplements, have been linked to these erroneous results. Antihistamines, such as brompheniramine and promethazine, and even the heartburn medication ranitidine, have been reported to cause false positive amphetamine readings. While some herbal supplements like yohimbe and ginseng have been suggested to mimic amphetamines, studies have also indicated that many common herbal products do not produce false positives for amphetamines.
Other Contributing Factors
Beyond medications, other factors can contribute to a false positive for amphetamines. Certain food items can influence test results. Bananas, which contain dopamine, have been shown to lead to false positives for amphetamines due to structural similarities.
While poppy seeds are widely known for causing false positives for opiates, they do not typically cause false positives for amphetamines. Similarly, while environmental exposure to secondhand marijuana smoke can sometimes lead to false positives for THC, there is generally a very low chance of this occurring at levels that would trigger a positive result for amphetamines.
Addressing a Potential False Positive
If an initial drug screen yields a positive result for amphetamines, it is important to remember that this preliminary test, often an immunoassay, can be prone to cross-reactivity with other substances. The next step involves confirmatory testing, which is much more precise and can differentiate between actual amphetamines and other compounds.
Gas Chromatography/Mass Spectrometry (GC/MS) and Liquid Chromatography/Mass Spectrometry (LC/MS) are highly accurate methods used for this purpose. These advanced tests work by separating and identifying specific chemical compounds based on their unique molecular fingerprints, providing a definitive result.
When facing a potential false positive, disclosing all medications—prescription, over-the-counter, and dietary supplements—to the testing facility or medical review officer is advised. Providing this comprehensive list allows the laboratory to account for potential interactions and helps ensure that the confirmatory tests accurately resolve any initial ambiguities.