Updated 18 March 2013

Are hair drug tests accurate?

Hair specimens offer a non-invasive drug test, but can the results be trusted?

When promising British cricketer Tom Maynard died in front of a train, coroners did a number of tests on his body. Among these was a hair test that toxicologists said showed drug use, including ecstasy and “residues of cocaine consistent with almost daily use for several months,” according to a report on

The idea of someone being able to clip off a piece of hair and have it drug tested may seem far-fetched, but the use of hair in drug tests is common practice in some countries.

Currently in South Africa, hair drug analysis is mainly used for custody cases, explains toxicologist Dr Tim Laurens, manager of the forensic toxicology laboratory at the University of Pretoria. “It is of prime importance for the donor to provide written informed consent since hair testing may raise many ethical issues. It does not really have a place in workplace drug testing since it is not an indicator of current intoxication.”

How are hair drug tests done?

Because hair grows at an average rate of 1cm per month, a 3cm piece of hair can provide a record of drug use (or abstinence) over a 3-month period. For example, unlike urine tests, which may only be able to show up cocaine use for a few days, hair samples can show levels of cocaine after as long as three months. The drug traces are extracted from the hair and then analysed using Gas Chromatography – Mass Spectrometry (GC-MS).

Advantages of hair drug testing

According to the University of Pretoria, which offers this type of testing, these are some of the advantages of this method of drug testing:
•    Hair testing offers a longer window of detection - months instead of days
•    The likelihood of tampering is reduced
•    Collecting of samples is simpler and more dignified than urine tests
•    Because of the longer period of detection, hair testing differentiates between once-off incidents and chronic substance abusers

What are the disadvantages?

In the opinion of Imelda Neate of Drug Testing South Africa, the technique should only be used for criminal and custody cases. Some of the limitations of this type of test, according to Neate are as follows:
•    It is easily evaded by shaving off bodily hair
•    Hair testing only provides potential long-term usage and may not detect recent drug use
•    The test is insensitive for detection of occasional use, especially marijuana
•    There is a concern about hair colour bias (darker hair may show higher concentrations)
•    Hair tests do not currently detect alcohol
•    There may be long waiting periods for test results.

Following Maynard's death, reports have suggested that hair drug testing may become more commonplace for high-level cricketers in the United Kingdom.

SOURCES: Dr Tim Laurens, Imelda Neate,,, University of Pretoria

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