Drug testing for cannabis

According to the Irish National Drug and Alcohol Survey 2019-20, cannabis is the most used drug in Ireland, with 40.3% of respondents admitting they personally knew somebody who used cannabis.

It is also highly detectable using drug tests and can be found in urine, saliva, and hair, as well as nail clipping samples.

In this article, we discuss cannabis drug testing, and how cannabis can be detected by different drug testing methods.

How long does it take for cannabis to show up in a drug test?

Cannabis use can be detected by a drug test long after the drug was first consumed.

There are a variety of drug testing methods available that can be used to test for the presence of cannabis, with detection windows as follows:

  • Oral fluid (saliva) – up to 48 hours after consumption
  • Urine – up to 4 days after consumption
  • Hair – up to 12 months after consumption (depending on the length of hair available)
  • Nails – up to 12 months after consumption (up to 6 months for fingernails and up to 12 months for toenails)

Oral fluid and urine drug testing are known as ‘narrow-window’ forms of testing and can be used to detect drug use from approximately 30 minutes after consumption, up to a few days.

However, this can vary depending on the type of substance and how much was used.

The rate at which hair and nails grow means that both hair drug testing and nail drug testing can provide a ‘wide-window’ of detection for drugs and their metabolites (up to 12 months).

Urine drug testing for cannabis

Urine drug testing is the quickest method for determining whether someone has been using cannabis.

This type of drug test involves collecting a sample of the donor’s urine in a self-contained screening pot, which indicates the presence of substances via built in test strips.

The results of the test are visible on the side of the pot within a few minutes.

This rapid form of drug testing is ideally suited where an immediate result is required and is known as a ‘narrow-window’ form of drug testing.

Urine drug tests can detect a single use of cannabis for up to four days after it has been consumed. Chronic heavy use of cannabis can be detected up to 30 days after being ingested using the same urine drug testing methods.

Oral fluid drug testing for cannabis

Oral fluid drug testing is a type of drug test that can be used to detect the presence of drugs in a saliva sample.

The test involves placing an absorbent collection device (like a large swab) inside a person’s mouth for a few minutes, to soak up enough saliva for analysis.

As with urine testing, oral fluid drug testing provides a ‘narrow-window’ of detection and is ideal in instances where a rapid test is required to determine cannabis use.

The test can detect cannabis use within approximately 30 minutes of consumption, up to 48 hours.

Hair drug testing for cannabis

Hair drug testing – also known as hair strand testing or hair follicle testing – is the gold standard in toxicological analysis.

Hair drug testing works by analysing a cut hair sample (head hair or body hair) for the presence of drugs and their metabolites and is known as a ‘wide-window’ form of drug testing, enabling us to determine a history of drug use for up to 12 months after consumption.

When a person takes drugs, they are broken down by the liver and a proportion of the drug and its metabolites are released into the bloodstream.

These drugs then enter the hair follicle and become trapped in the medulla, the innermost layer of the hair shaft. These substances remain trapped in the hair as it grows, making hair drug testing an effective method for establishing a history of cannabis use.

There are two methods available for hair drug testing: segmented analysis (head hair) and overview analysis (head hair or body hair).

Segmented analysis is the most detailed form of hair strand testing for drugs, which involves segmenting the hair into 1cm sections for a month-by-month profile and a more detailed history of cannabis use.

This method can be used to identify a trend in cannabis use, such as an increase or decrease over time, or to highlight intermittent use. It can be used to determine a history of cannabis use for a period of up to 12 months, depending on the length of hair available.

Overview analysis is beneficial if you are looking to obtain a more general insight into a person’s cannabis use. This is because any episodes of drug use are averaged out over the period being tested.

The maximum length of hair that can be tested to provide an overview of drug use is 3cms, which provides an overview of three months.

The maximum overview period that can be provided is 12 months. However, this would be reported as 4 x 3-month overviews, rather than one 12-month overview.

Unlike urine drug tests and saliva drug tests, hair strand analysis cannot show recent drug use. This is because it can take 7-10 days for the hair containing the drug to grow above the scalp and up to 14 days before it can be included in a cut sample.

Environmental exposure to cannabis can also be detected using hair strand analysis. For example, if an individual has been in an environment heavily laden with smoke.

Each hair sample is chemically washed three times to remove any drug present prior to analysis. If a donor admits to being surrounded by cannabis smokers, the washing solution could be used to back up any test results.

Nail drug testing for cannabis

Nail drug testing is known as a ‘wide-window’ form of drug testing, enabling us to determine a history of cannabis use for up to 12 months after consumption.

When a person takes drugs, they are broken down by the liver and a proportion of the drug and its metabolites are released into the bloodstream.

These substances then pass to the blood vessels below the nail, and into the nails themselves where they become trapped in the keratin fibres of the nail.

Unlike hair drug testing, nail drug testing for cannabis cannot provide a historic segmented pattern of drug use.

However, nail testing is an extremely reliable method for determining whether a person has used drugs in the six- or- 12-month period prior to the samples being collected.

Fingernails and toenails grow at different rates, with fingernails providing an approximate six-month overview of drug use, and toenails providing an approximate 12-month overview.

Drug testing for cannabis

We have been providing drug testing solutions for family law professionals, social workers and local authorities for over 15 years, including sample collection and analysis at our accredited laboratory.

We also offer free sample collection for legally-instructed drug tests at our Dublin walk-in centre.

If you require a cannabis drug test, or simply need advice on which test is best for your client, call our Legal team on 01 402 9466 or email and a member of the team will be in touch to discuss your requirements.

Legal Drug Testing

Explore our accredited drug testing services for family law professionals, social workers and local authorities.

Marie Law AlphaBiolabs

Marie Law

Head of Toxicology at AlphaBiolabs

A highly-skilled and respected scientist with over 13 years’ experience in the field of forensics, Marie joined AlphaBiolabs in 2022 and oversees the company’s growing toxicology team.

As Head of Toxicology, Marie’s day-to-day responsibilities include maintaining the highest quality testing standards for toxicology and further enhancing AlphaBiolabs’ drug and alcohol testing services for members of the public, the legal sector, and the workplace sector.

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