"Several collection devices have been manufactured for collecting sweat specimens. The two most common are the patch and the swipe; however, the sweat patch is the only device approved by the U.S. Food and Drug Administration (FDA). The quantity of sweat collected is determined by the length of time the patch is worn and the physiology of the person wearing the patch. The patch should be worn for at least 3 days, but no longer than 7 days, although most drugs will have been excreted within the first 48 hours (Barnes et al., 2009; Huestis et al., 2008; Kacinko et al., 2005; Schwilke et al., 2006). This ensures that a sufficient amount of sweat is collected for testing. The sweat collected with the patch detects drug use that occurred shortly before the patch was applied and while the device remains on the skin."


"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. Departent of Health and Human Services, 2012), p. 21.