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Can You Drive After Smoking Weed? No Absolutely Not.

The Problem

Like the Eagles, a surprising number of people think it is ok to drive after taking cannabis (the ‘colitas’ in their song are said to refer to cannabis buds). They know deep down it makes you woozy but they still want to believe it’s alright. Yet, the facts are clear. Cannabis makes you drive dangerously and the penalties are severe. You should not do it. Music superstar George Michael found that out in 2010 when he received an eight week jail sentence for a cannabis-fuelled DUI, after crashing his Range Rover in Hampstead, London. 

Unpredictable Effects of Cannabis

Cannabis can cause hallucinations, mood changes, confusion and disorientation. Most people behave more impulsively and find it harder to concentrate after using, and memory loss is common as well. All these responses are dangerous for car drivers, even when appearing at a low degree of severity.  

Cannabis Varies in Strength

The strength of cannabis varies greatly and is seldom fully known by the user. Moroccan hashish production for example has seen a decline in volume over recent years but a marked increase in strength. This can have unexpected dangers for the user especially when swift evasive action is needed: 

When Can You Drive After Smoking Weed?

You might think you can drive straight after you’ve had a ‘joint’ or at least within a few hours of smoking it, but you would be quite wrong. 

The legal limit for cannabis (known officially as THC) allowed in your bloodstream when driving is a tiny 2 micrograms (mg). An ‘average’ sized joint is likely to put around 120mg into your system. That is far more than the legal limit – one single puff of cannabis effectively makes you illegal driver.  Moreover, smoking cannabis is illegal so any trace amount means you have broken the law.

How Long Must You Wait After Using Cannabis Before Driving?

Any drug, including alcohol and cannabis, is monitored in your system by what is called its ‘half-life’. This is the time it takes for the amount of drug in your system to reduce by half. For cannabis, this is difficult to compute because it contains many compounds that disperse at different rates. Other factors to be considered include your own BMI (body mass) and metabolism. An average joint can take twelve hours to reach an acceptable level but that could double to twenty-four for high strength THC. Heavy habitual cannabis users might need to wait longer, before they can legally drive. 

What Evidence Is Needed for a Conviction?

In March 2015, the law was changed to make it an offence to drive with one or more controlled drugs above a specified level in your blood. The change in Section 5 (A) of the Road Traffic Act means that the police no longer have to prove that a driver was impaired by drugs they have taken. Instead, they simply have to show that drugs had been in their system above the specified level. If it can be proven in court that a person was driving over the legal cannabis limit, there may be a conviction. 

What Are the Penalties for Driving Under the Influence of Cannabis?

Cannabis is still an illegal substance in many countries, including in the UK, and should you be caught driving above the tiny legal limit, there will probably be a minimum twelve-month driving disqualification with the possibility of up to six months in prison. Since the 2015 introduction of Section 5 (A) of the RTA, the number of convictions for THC present in blood has risen steadily from 2,346 in 2015 to 10,206 in 2019 – the most recent figures available. 

CBD and Driving

There are two different elements of cannabis, CBD (cannabidiol) and THC (tetrahydrocannabinol). CBD is legal and known for the good effects it has with pain relief and relaxation; it is common to see oils, creams and skincare products with CBD extract in. It is also legal to vape CBD in the UK. 

The United Kingdom approved the use of medical cannabis in 2018 after it was found that AIDS, some types of cancer and epilepsy could be treated with pain relief based on medical cannabis formulations. Medical cannabis is similar to THC and therefore can only be obtained on a doctor’s prescription which is strictly controlled. THC is most often associated with the negative physical and mental effects of cannabis. Un-prescribed products containing THC are illegal in the UK. 

Should the Driving Law Be Changed?

Despite some protests that the cannabis driving laws are excessively severe, there is no sign that the UK government is considering any relaxation. 

Should Cannabis Use Be Legalised?

It is reported that road traffic accidents rose by ten percent In Colorado after cannabis was legalised there. Colorado was the first US state to do this. The UK government is unlikely to change any part of the law relating to THC Cannabis but is reviewing the impact of medical use cannabis on driving and society as a whole. 

Can a Person Ever Use Cannabis Before Driving?

The permitted bloodstream level (2mg) is far too small to allow any legal use at all. The question is like asking: is it ever acceptable to drive without due care and attention? The answer is always ‘no’. A better question would be: how much trouble will I find myself in, if I am caught driving with cannabis in my bloodstream (above 2mg)? The answer to that is a lot. 

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