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Hair drug testing is routinely used in the forensic and family law fields and is considered the gold standard for providing a history of drug abuse. Head hair grows at an average rate of 1 cm each month; therefore, drug use can be established over a defined period depending on the length of hair selected. The accuracy of any hair drug analysis depends on both the sampling procedure and the laboratory techniques employed.

Getting a sample

Hair strand samples are normally collected by a qualified nurse or trained sample collector. The sample needs to be cut from the highest point of the scalp and needs to contain around 200 individual strands (about the width of a pencil). Ideally, it should be taken from a discrete area.

If head hair is not available alternative collection sites could be considered including pubic, underarm, chest, leg and beard hair. The growth rate of hair from these alternate sites differs from head hair and as such body hair cannot be used to determine a specific timeframe of drug use.

Hair drug tests

There are two types of head hair drug tests available: overview or segmented analysis.

An overview analysis can provide a general indication of drug use. This could range from 3 cm to identify drug use within that 3-month time period, up to 6 or even 12 months, dependent on the length of hair available. In an overview test, any episodes of drug taking are averaged out over the period being tested. For example, if an individual has not taken drugs for 5 months but then takes an excessive amount in 1 month, drug markers will be found along the entire length of the hair.

Segmented analysis provides a more detailed analysis and the episode of drug taking can be pinpointed to the actual month. In a 6-month segmented analysis, hair samples are sectioned into six segments of 1 cm to provide six individual monthly analyses. Segmented analysis is therefore especially useful if you need to obtain a trend in drug use, such as to see a decrease or increase, or to highlight intermittent use.

A more in-depth version of this article can be read on our Learning Centre.

AlphaBiolabs has a network of trained sample collectors able to take hair strand samples for free at its nationwide Walk in Centres. For expert advice on hair testing and other drug testing solutions, please call 0333 600 1300 or email us at