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Drug Driving (Cannabis) a complete guide

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Drug Driving Cannabis



What does the law say?


"The Crime and Courts Act 2013 inserted a new section 5A into the Road Traffic Act 1988 (RTA), which makes it an offence to drive, attempt to drive, or be in charge of a motor vehicle with a concentration of a specified controlled drug in the body above the specified limit. The offence came into force on 2 March 2015"


In England and Wales, there is a zero-tolerance policy when it comes to Drug Driving meaning if you have any amount of illegal drugs in your system it is illegal to drive regardless of whether you are impaired or not.

If you are convicted of Drug Driving you could face harsh penalties such as :

  •   A minimum 12-month driving ban.
  •   A criminal record.
  •   A fine of up to £5,000.
  •   A custodial sentence of up to 6 months
  •   An endorsement on your driving license that will remain for 11 years.

The only obligation to this is the medical use of cannabis but regardless you will need to prove that it was lawfully obtained and used correctly in accordance with medical instruction.

Drug Driving Cannabis


What is the legal limit for cannabis?



Although there is no set limit for cannabis there is for THC ( delta-9-tetrahydrocannabinol) which is the main psychoactive ingredient in cannabis. The limit set in the UK for THC is a mere 2 micrograms this is so low that even being exposed to secondhand smoke from a cannabis smoker could put you over the limit and lead to penalties.

The legal limit for alcohol is significantly higher than that for cannabis and is currently under consideration by the government this is due to cannabis's ability to impair driving at smaller levels compared to alcohol.


How long does cannabis stay in your blood?



Unlike alcohol where you can roughly work out how many units you have had to drink and how much of it is present in your system cannabis is different as it varies massively based on how frequently:

  • You use the substance,

  • The potency of THC present in the cannabis                                                                          Drug Driving Cannabis

  • Your own individual metabolism.

Generally speaking in occasional users THC levels should reach below 2 ug from a few hours to 24 hours of use and in heavy users it could take up to 48 hours. A good rule of thumb would be for occasional use to wait at least  48 hours before attempting to drive to be extremely conservative.


"How long before I can drive after smoking weed?"




Due to the nature of THC's half-life being dependent on numerous factors such as age, weight, genetics, metabolism, and frequency of use, it is extremely hard to put an exact figure on how long you should actually wait before driving. Also as cannabis is not regulated like alcohol it's hard to know how much you have ingested and the potency.

Generally, the average joint will contain around 120mg of THC and the half-life which is the time taken for half of the metabolites to be eliminated will entirely depend on many factors therefore the best option would be to be extremely safe and wait up to 48 hours or more depending on how frequently you use cannabis products.

Although in most people the level of cannabis will be reduced to under 2mg in a shorter amount of time as there is no accurate way of knowing it is always in your best interest to wait.

"The government is unable to provide any guidance on what amounts of dosage would equate to being over the specified limits. There are too many variables, such as physical characteristics, where each person will metabolize the drug at different rates. Eating or drinking will also influence the blood concentration"

- Government Website


How the police determine if you're over the limit


‘Drug Wipes’


In the past police were quite limited in their options for detecting whether someone was over the limit nowadays police use devices called Drug Wipes usually during roadside checks.

These wipes are used to detect cocaine and cannabis and if they're positive it indicates that the drug is present in the driver's system. Once confirmed you will be taken back to the station to undergo a more detailed test such as a blood test where if you fail and more than 2ug is present in your system you will be charged.

Bear in mind that the drug wipes do not check for how much THC is in your system but rather if there are any traces present therefore they are non-evidential and cant be used in court to prove impairment.Drug swabs




A drugalyser similar to a breathalyzer is a handheld device used by police to detect the presence of drugs in saliva. If the drugalyser produces a positive result you may be arrested and taken back to the station for further testing usually taking a blood sample. Unlike the drug wipes, the drugalyser can provide a more accurate picture of the levels of the drug present. Therefore it can be used in court as evidence.

Drug Driving


Do I have to give a blood sample at the police station?


Once you have been swabbed or drugalysed you will be taken back to the police station it is important to remember your rights you can't be forced into giving a blood sample and the police will require your consent in the matter however if you do not consent you will be charged with failure to provide which can result in the following penalties : 

  • A minimum 12-month driving ban

  • A fine (up to £5000)

  • A prison sentence of 6 months

  • A criminal record


Defenses for failure to provide


  • Incapacity - you were physically incapable to provide a specimen due to various reasons such as a disability

  • Phobia - In this case, you have a medically recognized phobia such as intense fear of needles or blood.

  • Panic attack- If you suffered from a  panic attack at the time the sample was demanded.


The blood sample procedure


  • Consent must be given in order for a sample to be taken

  • The driver should be informed that by not providing a sample they will be charged with failure to provide

  • The blood sample can only be taken by a qualified medical professional

  • Only one blood sample can be drawn

  • The sample can be split and half given to the driver for an independent analysis.


Our Defences


Post Consumption



This defense includes the driver stating that at the time of their test, they were not under the influence of drugs and only after driving were they impaired and over the limit. for example, if a driver fears that he/she may face a conviction for possession of cannabis products they may consume them before being stopped by the police in order to avoid a sentence meaning that in the duration of time that they were driving they were not over the limit. 

To prove post-consumption testimonies of witnesses who observed the driver's behavior can be used or more commonly we use toxicologists who play a critical role in providing objective scientific evidence on the presence of a drug and its effect on the driver. We would obtain an experts report from one of our experienced toxicologists to prove that the drug was present in the blood of the driver due to post-consumption, which provides us with a strong defense to use in court.


Errors in calibration



Calibration errors are errors made in the calibration of equipment used to measure THC levels by the laboratories.

Calibration is the process that ensures that the equipment is reliable and provides accurate results. The UKAS (United Kingdom Accreditation Service) recommends that calibration should be performed to high standards with low deviation.

Deviation measures the degree of variation in the measurements and having a low deviation ensures that results are accurate. If standard deviations in equipment are high this could mean high levels of inconsistencies within results and false positives. Proving that equipment wasn't properly calibrated would acquit the driver.


Defences to the Procedure




One of the most important aspects of forming a defense to a drug driving case is questioning whether the procedure was carried out correctly by the police if it wasn't then the case will be dismissed.

The most important documents are the MGGDB, MGDDE, and MGDDF these are procedural documents the police are required to accurately complete to maintain the reliability of blood and urine samples.

During our years of dealing with a multitude of Drug Driving cases a lot of the time due to inexperience, lack of funding and training many of the officers fail to complete the documents accurately which we challenge by requesting technical data packs and quality assurance certificates to question whether the procedure was followed correctly.

MGDDB       -  (Snippet of MGDDB)


Defences using consent



The police cannot coerce you into giving a sample as by law your consent is necessary and the choice must be yours if the police haven't provided you with adequate information or used coercion into forcing you into giving a sample this is against the law and therefore the case will be dismissed.

On the other hand, if you did provide a sample a document called  HORT/5 certificate must be completed by the healthcare professional which confirms your consent in providing a sample. The crucial part about this document is that on account of Section 16 RTOA 1988, the document must be served on defence seven days prior to the trial and if it isn't it will be considered invalid, and therefore the consent of you providing a sample cant be proven.

The only other way the court could prove this is by having the medical professional present which is highly unlikely. In decades of dealing with cases of this nature, we have yet to experience this scenario.


Passive Smoking





Researchers have studied the effect of secondhand cannabis smoke on nonsmokers. During the studies, nonsmokers and smokers were placed together in a well-ventilated room for three hours. The researchers tested the nonsmokers’ urine and blood and both the samples did contain THC.


Another study conducted by Edward J Cone showed that eight nonsmokers present in a closed area specifically a coffee shop in the presence of cannabis smokers tested positive for THC both in their blood and their urine.

- See Here

Due to the no-tolerance approach for Drug Driving and the threshold for cannabis being so low, it is extremely common that even if you were not smoking but were exposed to secondhand smoke you could be over the limit for THC. In a situation like this could be would only be viable to argue in front of the magistrates if you were unaware of you inhaling cannabis.

Although it sounds improbable a  situation like this could more than likely occur due to food products such as brownies or gummy confectionary containing the product you may have been offered a simple brownie from a friend not knowing that it contained cannabis and subsequently as you were on your way back home were stopped for the police and charged for drug driving.

Other situations could also occur if you were asleep at a party or at a friend's house and you were unaware of cannabis being smoked. Although the smell of cannabis is very distinct you may have been unaware since you were asleep and as you left you were stopped and charged.

In cases like these, we would have to obtain a report from one of our senior toxicologists who we work very closely detailing the likelihood of the scenario occurring and the effects of inhalation of the smoke.

If arguing passive smoking your case would be given a special reasons hearing where you would have the opportunity to plead not guilty on the basis of the report. Usually, in situations where the CPS has strong evidence against you, we will put forward passive smoking to mitigate any penalties and help you avoid a disqualification.


False Positives



As with all drug screenings and police testing no analytical method is 100% accurate therefore false positives are bound to occur one defense to drug driving specifically cannabis that we put forward is that a false positive occurred.

Studies have shown that the use of certain painkillers such as ibuprofen and Advil caused the secretion of an endogenous substance that inhibits cannabinoid binding to an antibody and therefore interfering with the tests and providing a false positive as well as the consumption of hemp-based products.

Also due to the lack of experience of staff and lack of funding of the laboratories in which the police conduct the screenings false positives can be quite common. You wouldn't believe it but many times staff within the laboratories are prone to simple mistakes such as mislabelling samples in cases like these we would usually obtain the analytical data pack from the prosecution and further analyze it to question whether any mistakes have been made in relation to the samples.





How many joints is 2μg/l?

Unfortunately, there is no clear answer to this as it depends on multiple varying factors.

What is the legal THC limit uk?

 2 micrograms per litre of blood (2ug)

Can you get points for Drug Driving?

Yes, you can receive up to 10 points for Drug Driving.


Contacting a specialist

Above, we have written a brief guide to your options when dealing with a case relating to cannabisand driving. If you have been charged with Drug driving and would like additional information or advice please don't hesitate to call us at : 

01484 599888

 As a specialist drug driving firm, we have built an infamous reputation for helping the everyday man or woman keep their license. From our decades of experience and firsthand experience dealing with a plethora of Drug Driving cases, we are more than well-equipped to guide you through the perplexities of your case.