Hair Drug Testing: How Detection Works

A hair analysis for drugs is considered to be particularly meaningful long-term evidence. While blood or urine tests usually only cover a comparatively short period of time, hair can provide information about whether certain substances were consumed over weeks or months. This is precisely why the method is often used for abstinence verification via hair analysis, in MPU, in official procedures or in safety-related professions.

What is important is that a usable hair analysis is not just any laboratory test. For MPU purposes, it must be carried out in accordance with the applicable CTU criteria and evaluated by a forensically accredited laboratory, usually in accordance with DIN EN ISO/IEC 17025.

The principle: How do drugs actually get into the hair?

After consumption, drugs and their breakdown products enter the body through the bloodstream. While the hair is formed in the hair root, the so-called matrix, active ingredients or metabolites can be stored in the resulting keratin structure.

Once the hair grows out of the scalp, this chemical information is largely retained in the hair shaft. That’s why hair is often referred to as the body’s “long-term memory”. The analysis therefore does not examine the current state of intoxication, but retrospectively a period of time that depends on the length of the hair segment examined.

In addition, substances can also get onto the hair from outside, for example through smoke, sweat, sebum or dust. Reputable laboratories take this risk into account and therefore examine not only the main active ingredients, but also typical endogenous breakdown products.

Which substances can be detected?

Which drugs are tested during a hair analysis depends on the test profile ordered. So-called poly-screenings are common, in which several classes of substances are examined at the same time.

Typical test groups are:

Cannabis
When it comes to cannabis, attention is paid, among other things, to THC and relevant degradation products. It is particularly important to distinguish between possible external contact and actual consumption.

Cocaine
Cocaine and its metabolite benzoylecgonine are among the frequently examined parameters. Contamination from smoke or dust can also play a role here, which is why the interpretation must be carried out in a forensically clean manner.

Amphetamines and methamphetamines
These include amphetamine, methamphetamine, MDMA, MDA and related substances, such as those associated with ecstasy or crystal meth.

Opiates and opioids
The substances that can be examined include heroin markers, morphine, codeine, methadone, buprenorphine, tilidine, tramadol or fentanyl, depending on the laboratory order.

Benzodiazepines
Sedatives and sleeping pills such as diazepam, oxazepam, lorazepam or alprazolam can also be part of an extended profile.

Special case of alcohol: EtG in the hair
When detecting alcohol, it is not “alcohol” itself that is looked for, but ethyl glucuronide, or EtG for short. The EtG detection in hair serves as a marker for alcohol consumption, but is to be assessed differently than drug screenings.

Detectability: How far back does hair analysis go?

The most important rule of thumb is: hair grows on average about 1 centimeter per month. This results in the approximate look-back period.

A 3 cm long hair segment represents around 3 months. A 6cm strand can go back approximately 6 months.

In practice, clear limits apply to official or MPU-relevant proof of abstinence:

For drugs, a maximum period of 6 months is often assessed per hair analysis. For 12 months of abstinence, two examinations are usually carried out, each with a 6 cm hair segment.

With alcohol via EtG the period is shorter. A maximum of 3 cm or 3 months per analysis is generally accepted for alcohol abstinence because EtG is water-soluble and can wash out of the hair over a long period of time.

How far can drugs be detected in hair?

Since scalp hair grows about 1 centimeter per month, the length of the hair strand determines the detection period. A 3 cm long hair segment represents a period of 3 months, a 6 cm long strand corresponds to 6 months. Drug screening for official purposes such as the MPU generally does not look back beyond 6 months.

Hair removal process: Why you are not allowed to cut yourself

For a recognized proof of abstinence via hair analysis, it is not enough to cut off your own hair and send it to a laboratory. The removal must be traceable, identity-secure and tamper-proof.

Hair removal typically goes like this:

1. Identity verification with official ID
2. Documentation of the removal
3. Removal by trained personnel
4. Separate the sample as close as possible to the scalp
5. Shipping to an accredited laboratory
6. Analysis according to a specified examination order

The hair is usually taken from the back of the head, often in the occipital or tonsure area because growth there is relatively uniform. It is common to have several pencil-thick bundles of hair cut off directly at the scalp.

This external monitoring of hair removal is crucial. It is intended to ensure that the sample actually comes from the person being tested and was not subsequently exchanged or manipulated.

What happens if you are bald or have hair that is too short?

If head hair is not long enough, body hair can be used under certain conditions, for example chest, arm, leg or beard hair. However, for MPU purposes this is tricky.

Body hair grows more irregularly than head hair. In addition, the exact time period is often more difficult to segment. Some body hairs are examined in their entire length, which means that a longer and less precisely determinable period of time can be mapped. This can lead to problems if older consumption phases are still included.

Armpit and intimate hair are also often considered unsuitable due to increased contamination and sweat exposure. Anyone who needs a hair analysis for the MPU should therefore clarify with the assessment center or the abstinence program at an early stage which type of sample will be accepted.

Can you manipulate a hair analysis? Myths vs. Reality

Many people search for terms like manipulating hair analysis or “tricking hair analysis”. All that can be said seriously is that there is no reliable, legal way to safely falsify a forensic hair analysis.

Bleaching, dyeing and chemical treatments
Aggressive cosmetic treatments can influence the substance concentration in the hair. That’s exactly why they’re problematic. Laboratories and collection points request such treatments and may classify heavily treated or damaged hair as unusable. For proof of MPU abstinence, this can actually mean that the proof will not be recognized.

Special shampoos and alleged detox products
Drug metabolites do not simply sit on the surface of the hair, but can be embedded in the keratin structure. 99% of shampoos cannot reliably remove this deposit. Products that promise otherwise do not provide forensically reliable security.

Passive smoking and outside contact
With cannabis, cocaine or other substances, external contact can theoretically lead to adhesion to the hair. That’s why laboratories not only test for the original substance, but also for metabolites and evaluate the plausibility of the findings. Nevertheless, passive or unwitting contact can be problematic in abstinence programs. In practice, anyone who needs proof of abstinence should avoid relevant risk environments.

Which drugs cannot be seen in a hair analysis?

Modern forensic laboratories can detect many common illegal substances and medications using LC-MS/MS methods. However, very volatile substances or substances that are difficult to store in the hair, such as GHB or poppers, can only be detected extremely briefly or can hardly be reliably detected via hair analysis.

Can you do a hair analysis despite having your hair dyed?

Yes, a hair analysis is generally possible despite dyeing or bleaching. However, chemical treatments must be reported to the laboratory. Since aggressive hair coloring can artificially lower the drug concentration in the hair, laboratories reserve the right to classify severely damaged hair as unusable.

Colored, tinted or bleached hair is particularly critical for alcohol abstinence via EtG and may not be recognized depending on the location.

How much does a hair analysis for drugs cost?

The hair analysis drug costs depend on the laboratory, the scope of the examination and the purpose. A single alcohol EtG test is usually cheaper than an extensive drug screening with several substance classes.

The following apply as rough guidelines:

• Alcohol/EtG hair analysis: around 150 euros per sample
• Drug hair analysis: often around 190 to 300 euros per sample
• Extended profiles or additional reports can be more expensive

For an MPU, those affected usually have to bear the costs of proof of abstinence themselves. Additional costs may arise for advice, assessments and possible repeat analyses.

What you should pay attention to during an MPU hair analysis

If hair analysis is to be used for MPU, formal recognition is crucial. Make sure that:

• the examination is carried out according to current CTU criteria
• the sample is taken under external supervision
• a laboratory accredited according to DIN EN ISO/IEC 17025 is involved
• Hair length and examination period are planned correctly
• Chemical hair treatments must be clarified beforehand
• Medicines, nutritional supplements and risk products are documented

Unexpected problems can arise, especially with cannabis, CBD products, poppy products, medications containing codeine or cosmetics and medicines containing alcohol. Anyone going through an abstinence program should not deal with such points in passing, but rather discuss them in advance with the responsible authority.

Conclusion: The body’s incorruptible long-term memory

Hair analysis for drugs is a precise instrument if it is carried out correctly and interpreted in a professional manner. It does not show the current state, but can make consumption visible retrospectively over several months.

For the MPU or other official procedures, it is not just the laboratory result that counts, but also the entire chain of evidence: controlled collection, accredited laboratory, CTU-compliant implementation and usable hair material. Anyone who relies on recognized proof of abstinence is safest with timely planning, honest documentation and consistent cessation of consumption.

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Sources:
Bonn University Hospital: Proof of abstinence using hair analysis
TÜV NORD: Information sheet on hair analysis as proof of abstinence

Sources and further information

SAMHSA