Introduction to Hair drug testing

Hair drug testing is useful for detecting chronic and historical drug use, but cannot be used to detect current drug use. Hair drug testing is possible because metabolites circulating in the bloodstream are absorbed by the hair follicles and then transferred in trace amounts to the hair. Metabolites in a hair sample can be detected 7-10 days after the drug use. Metabolites in the hair remain there indefinitely, however the accepted practice is to only test for the previous three months. As hair grows at a rate of approximately 1cm per month, this means the sample taken is the 3cm from the base of the hair. For some substances hair testing can be used to analyse the history of drug use based on where in the hair metabolites are located, however some metabolites such as those of cocaine have been found to migrate along the hair making it unsuitable for this purpose for all substances.[1]

Advantages of Hair drug testing

• Long window of detection
• May be able to identify patterns of drug use
• Noninvasive sample collection
• Easy sample collection
• Four tests covers one year of use reducing costs

Disadvantages of Hair drug testing

• Cannot detect drug use in the preceding 7-10 days
• Complex and expensive laboratory analysis
• Possibility of environmental contamination of samples
• May be biased by hair colour and texture
• Point of care testing is not available

Methods used to subvert Hair drug testing

Commercial hair cleansing products

There are a number of products available that are used in case of an imminent drug test. Please do review the scientific literature about this, because the efficacy of these products has not been fully established. A list of commonly available products and anecdotal reports of the efficacy of the products may be found in the reviews section here.

Bleaching and hair treatments

Hair colour treatments are believed to have little impact on the ability to detect drug metabolites, however some evidence exists that bleaching and perming may reduce the volume of metabolites found in hair variably depending on the drug used. Methamphetamine in one study was found to have concentrations of metabolites reduced by 50% after five months with both treatments applied. The science is not very settled on this subject, so please do check the studies section for relevant research before committing to any such course of action. Please also do keep in mind that hair treatment immediately preceding an advised drug test may be treated as suspicious.[2]

Approximate detection window for common drugs using Hair drug testing

Unless otherwise noted the detection times listed here are for a single occasion use of a substance. Generally the detection cutoff thresholds are sensitive enough to detect any recreational dose for a non-tolerant user of these substances. Chronic administration usually leads to a build up of substances and their metabolites and consequently longer detection windows. Tolerance is not a significant factor in the elimination of the substance and its metabolites. Tolerance mostly reduces the pharmacodynamic response to a substance, rather than affecting the pharmacokinetic activity on the substance. This means that tolerant, chronic users of drugs are more likely to test positive regardless of whether they actually got high from the substance. Physiological differences such as kidney or liver impairment and the general metabolic rate can vary between individuals which can affect the detection window.

Substance	Detection window
Alcohol	n/a
Amphetamines	7-10 days to 90 days
Barbiturates	7-10 days to 90 days
Benzodiazepines	7-10 days to 90 days
Cannabis (single use)	7-10 days to 90 days
Cannabis (habitual use)	7-10 days to 90 days
Cocaine	7-10 days to 90 days
Codeine/Morphine	7-10 days to 90 days
Heroin (6-MAM)	7-10 days to 90 days
Hydrocodone/Hydromorphone	7-10 days to 90 days
Methamphetamine	7-10 days to 90 days
Oxycodone/Oxymorphone	7-10 days to 90 days
PCP	7-10 days to 90 days
GHB and prodrugs	7-10 days to 90 days
JWH-018 and JWH-073	7-10 days to 90 days

Note: The maximum window for detection is limited only by the length of the sample from the scalp taken. If a longer sample is taken a longer window of detection will apply.

Comparative detection windows for different types of sample can be found here

References

1. ^Center for Substance Abuse Treatment (U.S.) United States. Substance Abuse and Mental Health Services Administration. RTI International. Knowledge Application Program (U.S.). (2012). Clinical drug testing in primary care. Rockville, MD: U.S. Dept. of Health and Human Services, Substance Abuse and Mental Health Services Administration, Center for Substance Abuse Treatment.
2. ^Boumba, V. A., Ziavrou, K. S., & Vougiouklakis, T. (2006). Hair as a Biological Indicator of Drug Use, Drug Abuse or Chronic Exposure to Environmental Toxicants. International Journal of Toxicology, 25(3), 143-163. doi:10.1080/10915810600683028

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