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.