Drug Driving – Delta-9-tetrahydrocannabinol (Cannabis)

Delta-9-tetrahydrocannabionol (THC) is the  drug is found in cannabis and it is what gives the user a sense of euphoria.

THC’s chemical structure is like one of the brain’s natural chemicals, anandamide, so it allows drugs to be recognized by the body and to alter normal brain communication.

It can also cause memory loss and induce hallucinations and create feelings of paranoia. drug is found in cannabis and it what causes the cells in the brain to release the pleasure chemical “dopamine” which gives the user a sense of euphoria.

The threshold limit in microgrammes per litre of blood (µg/L) is 2µg/L in respect of Drug Driving offences. 

The police currently use devices known as ‘Drug-wipes’ to test for cocaine and cannabis at the roadside. They come with clear instructions, but time and time again the police manage to make mistakes. 

A roadside Drug-wipe will not test for impairment, it will only test for traces of cannabis and cocaine. You could fail the test even if you’re not impaired. These tests are non-evidential and they do not show whether you exceed the prescribed limit.

THC is not easy to detect in blood. This presents practical problems for laboratories when trying to analyse blood and produce accurate results. 

  • Method of Analysis

    The most common method of analysis for THC is Gas-Chromatography Mass-Spectometry (GC-MS). This is considered the best in commercial drug testing. The laboratory is still required to deduct 30% from the measured result to allow for ‘normal analytical variation’.

    One has to question that if this method of analysis is as accurate as alleged then why is their a requirement to reduce the result by one third. This indicates the potential for unreliable results.  If the laboratory has failed to deduct this amount, you could be wrongly (and unfairly) charged with drug driving.
  • Quality Control and Quality Assurance Procedures

    Laboratories wishing to undertake drug testing of this type are required to attain accreditation and part of this validation process requires laboratories to frequently measure their analytical performance in terms of accuracy and precision (due to the huge margin for error with drug analysis).

    It is the case that a leading UK laboratory has failed a number of quality control and assurance tests and has had its accreditation revoked, but a question remains – Are they still involved?

  • Calibration & Standard Deviation

    Laboratories are required to calibrate testing instruments at the beginning of each day. This process involves analysing a number of solutions (calibrants) each containing a different known drug concentration. The results of the calibration test are then plotted to produce a calibration graph. These results must fall within a validated range.  I have found that the concentrations of THC used to prepare calibration graphs in some cases have not complied with the accreditation analytical requirement.

  • False Positives

    No analytical method is 100% accurate. False positives do occur.

    Positive results may be obtained by consumption of non-psychoactive substances, such as Hemp Seed Oil and some forms of Vitamin B. Some conditions can also cause reactions in the body that may produce similar metabolites to THC. Often the most common cause of false possible results to arise out of human error. Labelling errors, inadequate training, staff fatigue and all reasons given by laboratories in cases involving false positive readings.

Overall it is very important to check the accuracy of your blood results. Please don’t make the mistake of simply assuming the results are correct. Mistakes happen more often than you might realise.

Passive Smoking – Cannabis

Secondhand exposure to cannabis smoke can produce positive drug tests.  It is important to note that passive-smoking of cannabis is not a defence. It could only amount to a ‘special reason’.

This is because in any case cannabis would be present in your system above the prescribed limit of 2 microgrammes.

However if this was argued successfully, it could result in you avoiding a ban.

If you would like more information about Drug Driving defences please email jbrown@nechambers.co.uk or phone 0191.4862799

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