"The parent drug is usually found in oral fluids, although the metabolite(s) may be present and quite useful. The parent drug is generally found in higher concentrations in oral fluids than are drug metabolites. Compared with urine specimens, oral fluid specimens present fewer opportunities for adulteration or substitution (Dams, Choo, Lambert, Jones, & Huestis, 2007). Use of commercial adulterants or mouthwashes were not found to interfere with the immunoassay (Bosker & Huestis, 2009), or they did not affect test results if the products are used more than 30 minutes before specimen collection (Drummer, 2006; Niedbala, Kardos, & Fries, et al., 2001; Niedbala, Kardos, Fritch, Cannon & Davis, 2001). The window of detection for oral fluid is narrower than it is for urine, and drug concentrations are generally lower (Warner, 2003). In general, drug testing of oral fluids detects drug use during the previous 24–48 hours, regardless of the route of administration (Cone, 2006), although the selection of cutoffs plays an important role in the length of the detection window.
"Oral fluid collection devices vary, but the most common version is a swab or absorbent pad on a stick that is placed between the lower cheek and gums to collect fluid and is left in place for a few minutes. It is then inserted into a vial containing a buffer solution for shipment to the laboratory. POCTs [Point Of Care Tests] are also available for oral fluid testing."


"Clinical Drug Testing in Primary Care," Technical Assistance Publication (TAP) 32, Substance Abuse and Mental Health Services Administration, Clinical Drug Testing in Primary Care (Rockville, MD: U.S. Department of Health and Human Services, 2012), p. 20.