The objective of this study is to determine whether R(-)-methamphetamine inhaled from nasal inhalers produces positive methamphetamine results in currently used urine drug screening procedures and to present a rapid method for distinguishing the optical isomers of methamphetamine. Urine from three subjects inhaling from a Vicks Nasal Inhaler every 20 min for six hours tested positive for methamphetamine by EMIT, Toxilab, TDx, and GC/MS. The chiral derivatizing reagent N-trifluoroacetyl-L-prolyl chloride (L-TPC) was used to form methamphetamine diastereomers allowing rapid identification of each stereoisomer of methamphetamine present in the urine samples. Urine samples positive for amphetamines during routine drug screening were determined to consist of a racemic mixture of methamphetamine. The isomeric composition of methamphetamine present in a urine sample indicates the probable source of the drug.