What medications can cause a false positive for methamphetamines?
A false-positive test result means that your drug test shows the presence of a medication or substance that you aren't actually taking. For example, a methamphetamine test comes back positive for methamphetamines, even though you haven't taken any.
False-positive results can be due to a laboratory error, but the most common reason for a false-positive methamphetamine test is other medications or substances that have a similar structure to methamphetamine.
Immunoassay testing for methamphetamine uses antibodies to look for certain drug metabolites (these are the compounds a drug breaks down into), and is the most common test used for initial screening. However, these antibodies may detect drug metabolites with similar structure and characteristics to methamphetamine, leading to false-positive results. For this reason, immunoassay testing should only be considered preliminary and should be followed up by confirmatory testing whenever a test comes back positive. Confirmatory tests are much more specific, but are costly, take more time, and require experienced laboratory personnel. They can distinguish between the l- and d-isomers of methamphetamine (only the d-isomer is psychoactive and illegal).
Usually, an immunoassay screening test for methamphetamine is a methamphetamine/amphetamine combined test, so will detect any medication or substance that resembles methamphetamine OR amphetamine. Medications that have been reported to cause false-positive results for methamphetamine or amphetamine include:
- Amantadine, a drug that can prevent the flu and treat symptoms of Parkinson’s disease
- Aripiprazole, an antipsychotic drug
- Atomoxetine, an ADHD treatment
- Brompheniramine, an antihistamine
- Bupropion, an antidepressant
- Chlorpromazine, an antipsychotic drug
- Desipramine, an antidepressant
- DMAA (1,3-dimethylamylamine), found in some dietary and weight-loss supplements
- Ephedrine, a medication that treats low blood pressure from other medications
- Fenofibrate, a cholesterol-lowering medication
- Fluoxetine, an antidepressant
- Labetalol, a blood pressure-lowering drug
- Metformin, a diabetes medication
- Nefazodone, an antidepressant
- Ofloxacin, an antibiotic used to treat ear infections
- Promethazine, a drug that treats allergies and/or motion sickness
- Pseudoephedrine, a decongestant
- Ranitidine, a drug used for ulcers and gastroesophageal reflux disease (discontinued in 2020)
- Phentermine, a weight loss drug
- Phenylephrine, a decongestant
- Selegiline, a drug for Parkinson's disease or depression
- Trazodone, an antidepressant/sedative
- Thioridazine, an antipsychotic drug
- Vicks Inhaler, contains l-methamphetamine, an isomer of methamphetamine useful for nasal congestion that is legal because it has little activity in the brain.
- Saitman A, Park H-D, Fitzgerald RL. False-Positive Interferences of Common Urine Drug Screen Immunoassays: A Review. Journal of Analytical Toxicology. 2014; 38(7): 387–396. https://doi.org/10.1093/jat/bku075.
- University of Illinois-Chicago Drug Information Group. What drugs are likely to interfere with urine drug screens? May 2021. Available at: https://dig.pharmacy.uic.edu/faqs/2021-2/may-2021-faqs/what-drugs-are-likely-to-interfere-with-urine-drug-screens/. [Accessed 18 August 2022].
- DeGeorge, Jr. M, Weber J. Methamphetamine Urine Toxicology: An In-depth Review. Pract Pain Manag. 2012;12(10). https://www.practicalpainmanagement.com/treatments/pharmacological/non-opioids/methamphetamine-urine-toxicology-depth-review
- Did A “Vicks Inhaler” Cause My Positive Test? Nationwide Testing Association Inc. https://ntatesting.com/did-a-vicks-inhaler-cause-my-positive-test/
- Roopa Sethi, MD; Amad Din, MD, MPH; Ryan McAllister, MD; and Andrew Lester, MD. I Have Never Used Methamphetamine, But My Urinalysis Says I Do. October 18, 2018. Psychiatrist.com https://www.psychiatrist.com/pcc/addiction/substance-use-disorders/i-have-never-used-methamphetamine-but-my-urinalysis-says-i-do/#:~:text=1%2D4%20Common%20medications%20that,bupropion%2C%20trazodone%2C%20and%20chlorpromazine.
- Ferguson M, Borowiak E. Ask the Expert: False Positive Amphetamine Urine Screens. Pract Pain Manag. 2015;15(1). https://www.practicalpainmanagement.com/resources/diagnostic-tests/ask-expert-false-positive-amphetamine-urine-screens
- Fenderson, J. L., Stratton, A. N., Domingo, J. S., Matthews, G. O., & Tan, C. D. (2013). Amphetamine positive urine toxicology screen secondary to atomoxetine. Case reports in psychiatry, 2013, 381261. https://doi.org/10.1155/2013/381261
- Merigian, K. S., & Browning, R. G. (1993). Desipramine and amantadine causing false-positive urine test for amphetamine. Annals of emergency medicine, 22(12), 1927–1928. https://doi.org/10.1016/s0196-0644(05)80433-0
- Caricasole, V., Spagnolo, G., Di Bernardo, I., Cirnigliaro, G., Piccoli, E., & Dell’Osso, B. (2019). Aripiprazole causing false positive urine amphetamine drug screen in an adult patient with bipolar disorder. Comprehensive Psychiatry, 94, 152126. https://doi.org/10.1016/j.comppsych.2019.152126
- Schwebach a, Ball J. Urine Drug Screening: Minimizing False-Positives and False-Negatives to Optimize Patient Care. August 18,2016. U.S. Pharmacist. https://www.uspharmacist.com/article/urine-drug-screening-minimizing-false-positives-and-false-negatives-to-optimize-patient-care#:~:text=The%20FGAs%20chlorpromazine%2C%20prochlorperazine%2C%20haloperidol,cause%20false%2Dpositive%20LSD%20results.&text=Thioridazine%20may%20additionally%20cause%20false,in%20structure)%20and%20methadone%20results.
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