Editing Drug test (section)

===Hair drug testing===
Hair drug testing is a method that can detect drug use over a much longer period of time than saliva, sweat or urine tests. Hair testing is also more robust with respect to tampering. Thus, hair sampling is preferred by the US military<ref name=idk38>{{Cite thesis|last=Hatala|first=John W.|date=June 2003|title=The Feasibility of Testing Hair for Illicit Drug Use in the United States Marine Corps|place=Monterey, California|publisher=[[Naval Postgraduate School]]|pages=2|url=http://www.usna.edu/IR/htmls/lead/database/cohort6/c06_hatala.pdf|access-date=May 7, 2009|hdl=10945/976|hdl-access=free|archive-date=January 17, 2009|archive-url=https://web.archive.org/web/20090117085241/http://www.usna.edu/IR/htmls/lead/database/cohort6/c06_hatala.pdf|url-status=live}}</ref> and by many large corporations, which are subject to [[Drug-Free Workplace Act of 1988]].

Head hair normally growth at the rate of 0.5&nbsp;inches per month.<ref name="zme">{{cite web |url=https://www.zmescience.com/other/science-abc/how-fast-hair-grows-042394/ |title=How fast hair grows, and other hairy science |last=Puiu |first=Tibi |date=August 23, 2018 |website=zmescience.com |publisher=ZME Science |access-date=September 28, 2018 |quote=The hair on your head grows about 6 inches a year. |archive-date=August 30, 2018 |archive-url=https://web.archive.org/web/20180830142322/https://www.zmescience.com/other/science-abc/how-fast-hair-grows-042394/ |url-status=live }}</ref> Thus, the most common hair sample length of 1.5" from the scalp would detect drug use within the last 90-100 days. 80-120 strands of hair are sufficient for the test.<ref name="i910">{{cite book | title=Analytical and Practical Aspects of Drug Testing in Hair | publisher=CRC Press | date=2006-08-30 | isbn=978-0-429-24525-1 | doi=10.1201/9781420006193 | page= | editor-last1=Kintz | editor-first1=Pascal }}</ref> In the absence of hair on the head, body hair can be used as an acceptable substitute. This includes facial hair, the underarms, arms, and legs or even pubic hair. Because body hair usually grows slower than head hair, drugs can often be detected in body hair for longer periods, e.g. up to 12 months. Currently, most entities that use hair testing have prescribed consequences for individuals removing hair to avoid a hair drug test.

Most drugs are analysed in hair samples not as the original psychoactive molecules, but rather as their metabolytes. For example, [[ethanol]] is determined as [[ethyl glucuronide]], while [[cocaine]] use is confirmed using [[ecgonine]]. Testing for metabolytes reduces the likelihood of false positive results due to contamination. One disadvantage of hair testing is, that it cannot detect recent drug use, because it takes at least a week after a drug intake for the metabolytes to show up in a growing hair above the skin.<ref name=idk38/> Urine tests are better suited for detecting recent (within a week) drug use.

In a practical test, hair sample is usually washed with a low polarity solvent (such as [[dichloromethane]]) to remove surface contaminations. Then, the sample is pulverized and extracted with a more polar solvent, such as methanol.<ref name="h623">{{cite journal | last1=Musiał | first1=Jadwiga | last2=Powierska-Czarny | first2=Jolanta | last3=Czarny | first3=Jakub | last4=Raczkowski | first4=Michał | last5=Galant | first5=Natalia | last6=Buszewski | first6=Bogusław | last7=Gadzała-Kopciuch | first7=Renata | title=One-step extraction and determination of 513 psychoactive substances, drugs, and their metabolites from hair by LC–MS/MS | journal=Archives of Toxicology | volume=96 | issue=11 | date=2022 | issn=0340-5761 | pmid=36008489 | pmc=9525419 | doi=10.1007/s00204-022-03343-w | pages=2927–2933| bibcode=2022ArTox..96.2927M }}</ref>

Although thousand different substances can be determined in a single [[gas chromatography–mass spectrometry]] or [[liquid chromatography–mass spectrometry]] experiment, due to the low concentration of analytes, practical measurements (see [[Gas chromatography%E2%80%93mass spectrometry#Selective ion monitoring|selective ion monitoring]]) are limited to a smaller number (10-20) of analytes. [[Designer drugs]] are usually missed in such measurements, because the analyst must know in advance what chemicals to look for.

Most hair testing laboratories use the aforementioned [[chromato-mass-spectrometry]] methods for confirmation or for rarely tested drugs only. Mass screening (preliminary or final) is usually done with [[immunoassays]], because of their lower cost.