Evaluation of the 20% D-methamphetamine requirement for determining illicit use of methamphetamine in urine.

In urine drug testing, enantiomer analysis is used to determine whether a positive methamphetamine result could be due to use of an over-the-counter (OTC) nasal inhaler containing L-methamphetamine. D-methamphetamine at more than 20% of the total is considered indicative of a source other than an OTC product. This interpretation is based on a 1991 Department of Health and Human Services (HHS) Technical Advisory.