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How much hair is needed for a drug test?
By Karolina Baker, Health Testing Specialist at at AlphaBiolabs
Last reviewed: 05/09/2023
Court-ordered drug tests take place every day in Ireland and hair drug testing is the most effective way to determine a person’s pattern of drug use over a period of up to 12 months.
What is hair drug testing?
A hair drug test is used to analyse samples of hair, originating from the head or body, for the presence of drugs and their metabolites (breakdown products).
Upon consumption, drugs enter the bloodstream. Through the bloodstream, the parent drug and its metabolites travel to the hair follicles, where they are deposited and remain within the hair shaft as it grows.
Therefore, when the hair is analysed by the toxicology laboratory, the parent drug and/or its metabolites will be identified within the hair.
How does hair drug testing work?
Hair drug testing can be used to examine cut hair samples for the presence of drugs and drug metabolites.
When a person ingests drugs, the drug and/or its metabolites enter the bloodstream, and as a result enter the hair follicles. They become entrapped within the innermost layer of the hair shaft known as the medulla. As a result, a toxicology laboratory can detect drugs within a cut hair sample for a period of up to 12 months.
We know that head hair grows at an average rate of 1 cm per month, and that it takes approximately 7-10 days for hair to grow above the surface of the scalp. As a result, the toxicology laboratory uses these statistics to calculate the month-by-month pattern of drug consumption for a defined period of time.
There are two methods available for head hair drug testing: segmented analysis and overview analysis.
Segmented analysis is the most detailed form of hair strand testing for drugs. The collected hair sample is segmented into 1cm sections, allowing toxicology scientists to determine a detailed, month-by-month, history of drug use. Segmented analysis is therefore particularly helpful for identifying trends in drug use, such as intermittent use, or the increase and/or decrease of drug consumption over time.
Segmented analysis can be used to identify patterns in drug use for a period of up to 12 months.
The table below shows how segmented analysis can be used, and how many segments of hair would be required according to the period being tested:
| Segmented analysis required (months) | Number of segments (1cm per segment) | Reported time period |
| 1 | 1 | 1 month |
| 3 | 3 | 3 individual months |
| 6 | 6 | 6 individual months |
| 9 | 9 | 9 individual months |
| 12 | 12 | 12 individual months |
The maximum length of hair that can be tested to provide an overview of drug use is 3 cm, which provides an overview of three months.
The maximum overview period that can be provided is 12 months, which will be shown as 4 x 3-month overviews.
The table below shows the options available for hair drug testing using overview analysis, and what will be shown in the report, depending on the required overview period:
| Overview analysis required (months) | Number of segments (3cm per segment) | Reported time period |
| 3 | 1 | 3 months |
| 6 | 2 | 2 x 3-month periods |
| 9 | 3 | 3 x 3-month periods |
| 12 | 4 | 4 x 3-month periods |
It is important to consider that in a hair strand overview test, an individual could test positive if they have abstained from drugs for 2 out of the 3 months, but ingested drugs within the other month, as the result is calculated as an average consumption over the defined period.
How does hair grow?
Hair grows from the root that is located at the bottom of a follicle and under the skin. Hair growth is stimulated by keratin (the protein that hair is made of), and head hair grows at a rate of around 1 cm per month.
The hair growth cycle consists of four stages, but the anagen (growing) phase lasts for several years resulting in continuous growth. Once the growing phase ends, the hair bulb begins to degenerate (catagen phase). The hair stops growing but remains within the skin for 2-6 months (telogen phase) until a new hair is formed, and the old hair falls out.
For hair drug testing, it takes approximately two weeks for newly-formed hair containing the drug to be detected within a cut hair sample.
Scalp hair from the posterior vertex is the preferred sample for hair strand drug testing as it has the most consistent growth rate and contains the largest proportion of follicles in the anagen (growing) phase.
How much hair is needed for a hair drug test?
There are two types of hair strand drug testing, segmented analysis, and overview analysis.
The amount of hair required depends on:
- the type of test requested – whether it is a segmented or overview analysis
- the time period tested for (up to a maximum of 12 months)
As a result, the sample required can range from 1 – 12 cm of head hair.
As a minimum, hair should be at least 1 cm in length (head or body). Around 200 stands of hair (about the width of a pencil) are required for accurate analysis.
Two samples are generally required for standard testing.
Can body hair be used if head hair is not available?
If head hair is not available, it is possible to perform hair drug testing on body hair of at least 1 cm in length.
Body hair can only be used provide an overview of drug use for up to 12 months, but it is not suitable for detailed segmented hair strand analysis.
Where can I get drug hair test?
AlphaBiolabs has extensive experience providing hair drug testing services for local authorities, family law professionals and social workers.
All hair sample collections are performed under strict chain of custody conditions, and our test results are accepted by courts in in Ireland.
We also offer FREE sample collections for legally-instructed hair drug tests from our Dublin walk-in centre.
For expert advice or to request a quote for hair drug testing, call our New Enquiry team on 01 402 9466 or email testing@alphabiolabs.com.
Alternatively, complete our online quote form, and a member of the team will be in touch to discuss your needs.
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Karolina Baker
Health Testing Specialist at AlphaBiolabs
Karolina joined AlphaBiolabs in 2021, and holds the role of Health Testing Specialist.
As well as overseeing a range of health tests, Karolina plays an active role in the research and development of the company’s latest health test offerings.
Before joining AlphaBiolabs, Karolina worked as an Associate Practitioner at Mid-Cheshire Hospitals NHS Foundation Trust, and as a research assistant at the Turner Laboratory, within the Faculty of Biology, Medicine and Health at The University of Manchester.
Karolina’s main scientific interests include clinical genomics and genetic diagnostics. Her qualifications include a BSc in Molecular Biology and an MSc in Genomic Medicine.
