Hi, Thanks for writing in. Meth test might cross react with other chemicals. The swab test does not test for meth but tests for molecules which are breakdown products of meth. In this way the breakdown product of meth can be similar to any of the substances that are ingested by you and the test becomes positive. It can also become false positive due to taking some medications prescribed to you. Categories of medications included which cause false positive meth test include antihistamines, antidepressants, antibiotics, analgesics, antipsychotics, and nonprescription agents. Reports of false-positive results have been found for nonprescription medications like brompheniramine, bupropion, chlorpromazine, clomipramine, dextromethorphan, diphenhydramine, doxylamine, ibuprofen, naproxen, promethazine, quetiapine, quinolones (ofloxacin and gatifloxacin), ranitidine, sertraline, thioridazine, trazodone, venlafaxine, verapamil, and nasal inhaler. Please do not worry.