What is the cannabis drug driving limit?

Since the new “specified limit” drug driving offence came into force in March 2015, we’ve received a significant number of calls from worried motorists who are unsure of how much cannabis they are allowed to smoke, or how long they need to wait before getting behind the wheel of a car.

The drug driving limit for Cannabis:

The drug drive limit for THC (the active ingredient in cannabis) has been set at 2ng.

There is no current limit set for carboxy- THC (the cannabis metabolite).

How much weed can I smoke before reaching the cannabis drug driving limit?

cannabis drug driving limit, how much can you smoke

The UK drug driving limits have been set extremely low, at an almost zero tolerance level. The limits are so low that experts have suggested that one single puff on a joint would be enough to put you over the limit.

When the Government  considered setting the limit, it invited the views of a panel of experts to consult on what the limit should be. The experts suggested that the limit should by 5ng; over twice the limit that was eventually set.

With the extremely low limit in mind, we would recommend avoiding smoking cannabis if you know that you are going to be driving. There is no ‘safe’ limit; it would be impossible to try and set one. Even if the drug driving limit were higher, it would be impossible to say how much weed could be smoked before getting behind the wheel of a car: There are too many external differentials such as:

  • The strength and type of cannabis
  • The time taken to smoke the joint
  • Your height and weight
  • The rate at which your own body breaks down substances (your metabolic rate)
  • Whether you have any underlying medical conditions.

The list could go on and on.

How long do I need to wait after smoking a joint before driving?

There’s been much debate over how long you should wait after smoking cannabis before driving.

A great deal depends on how much you’ve smoked, how strong the cannabis is and how frequently you tend to smoke it. THC can be stored in fat cells; therefore it can typically take longer to leave the body than many other drugs.

Some sources suggest that the active THC is clear of the system in significant amounts within as little as two and a half hours, and other sources such as the NHS suggest that it can take up to two months for a heavy user of cannabis to display results that are free of THC. The question is whether the THC displayed in the results would be over the prescribed low limit of 2ng?

Under the older “Section 4 Road Traffic Act 1988 Driving whilst impaired through drugs” offence, cannabis users were able to rely on their own judgement to determine whether they were fit to drive. They could only be prosecuted if their manner of driving was impaired and the impairment was linked to evidence of a drug in their system.

Under the newest “Section 5A Road Traffic Act 1988 Specified limit drug driving offence” it’s a complete guessing game. The police can now charge you with drug driving even if you drove perfectly normally and showed no signs of drug use. All that they need to Prosecute is a positive specimen of blood which is over the specified limit.

Since the police no longer need to prove any impairment to charge you with a drug driving offence, it is absolutely vital that you leave as long as you can before driving if you have smoked cannabis.

We’ve represented many drivers who had only smoked a very small amount of cannabis the night before and were pulled over by the police for something very minor and later charged for drug driving.  Therefore we can add from the benefit of our experience that it really does not take a large quantity of cannabis to reach the low limits which are currently in place, and people are still showing signs of the drug in their system over the specified limit long after the effects have worn off.

Frustratingly, this leaves cannabis users in a situation where you might get behind the wheel of a car completely oblivious to whether you are committing a criminal offence or not. It seems the only way to be 100% sure that you avoid prosecution is to either never smoke cannabis or never drive a car. This vague non-solution seems to highlight the real purpose of the drug driving law – to clamp down on those who take drugs, not necessarily to tackle the effects of drug driving, since the law is not concerned whether your driving caused even the remotest danger to the public or to yourself.

What happens if I plead guilty to Drug Driving?

A conviction for drug driving could ruin your whole life. It’s a minimum 12 month disqualification from driving, a fine of up to £5000 and for the worst offenders, up to 6 months in prison. In the absence of formal sentencing guidelines to assist the Court in sentencing those who plead guilty or are found guilty, the Courts have already shown a willingness to send people to prison for committing this offence.

The offence would go down on your record as a criminal conviction and would appear on your driving licence as a drug driving offence for eleven years.

A drug driving conviction can cause problems travelling to countries such as America, and would need to be declared to certain future employers, particularly in professions such as medicine and the law.

A conviction for drug driving would also lead to significant future insurance premiums once you eventually got back on the road

Can a drug driving offence be defended?

At Ashworth Motoring law we are specialists in defending drug driving allegations, so much so that we have a 100% record in securing acquittals. Defences tend to centre on issues concerning the reliability of the Prosecution evidence (we are finding that there are serious issues concerning the way that many samples have been analysed) and concerning the procedure. For practical reasons we cannot list all potential defences in this article but would urge anyone who is considering defending a drug driving allegation to contact our helpline on 0330 33 22 770 for free initial advice from one of our expert drug driving solicitors.