"Additional controversies exist about whether biophysical attributes affect hair analysis. Studies have shown that concentrations of drugs in hair can be affected by variations in hair structure, growth rate, melanin content, hygiene, and cosmetic hair treatments, such as bleaching (Dasgupta, 2008). Although there have been a limited number of human clinical controlled studies, data show that higher concentrations of some drugs (e.g., codeine, cocaine, amphetamine) are found in dark hair compared with concentrations found in blond or red hair (SAMHSA, 2004). Cone and Joseph (1996) reviewed several articles and found that hair testing may be biased toward some hair types. Drugs of abuse bind more readily to Africoid and Mongoloid types of hair compared with Caucasoid hair. Cosmetic hair treatments also affect the binding of drugs to hair. For example, bleaching of the hair can reduce drug content, but it also can damage the hair to the extent that bleaching may increase binding of the drug to the hair (Skopp, Pötsch, & Moeller, 1997). Some drugs (i.e., THC) do not differentially distribute into hair based on melanin content (Smeal, 2007). Therefore, hair testing may not be the most equitable drug testing matrix. Hair rinses, bleaches, and shampoos that claim to interfere with drug tests are advertised on the Internet and in magazines."


"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. 22.