The UK’s new "zero tolerance" drug driving laws – what do they mean?


April 2, 2014

British drivers will soon face "zero tolerance" drug driving laws (Photo: Shutterstock)

British drivers will soon face "zero tolerance" drug driving laws (Photo: Shutterstock)

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The UK has put in place some of the strictest drug driving laws on the planet in an effort to get drug-impaired drivers off the roads. Breath screening and blood tests will be used to detect eight illicit drugs at "zero tolerance" levels, and eight further prescription drugs at levels that would begin to impair driving. Naturally, since the British government can’t be seen to encourage recreational drug use, these limits haven’t been put into a practical context. So we contacted several drug testing experts and a forensic pharmacologist to try to work out what they mean. And as it turns out, some drugs will make you illegal to drive long after their physical effects have worn off.

Driving limits for 16 different drugs have been approved in the UK and a testing process is now under development. The new limits tighten up and work in tandem with the existing system, in which police need to prove a driver is impaired through a roadside co-ordination test, and then prove that impairment was due to drug use.

How drivers will be tested

Drug screening will be done initially using Drugalyser oral swab tests, which test for chemical compounds in the saliva – and it appears that a positive saliva sample could lead to a blood sample test, taken at a hospital: “The police will use the new offence to prosecute drivers whose evidential blood samples contain more than the specified limits of those drugs provided for in regulations.”

UK drug driving penalties

Penalties will be stiff – up to six months in prison, up to £5,000 in fines and a license disqualification for at least 12 months. They're designed to be in line with drink driving penalties, and not to punish people for having illegal drugs in their system, which is not illegal in itself.

So, what do these limits mean for the average British drug user? The main takeaway as far as illegal drugs go is that the limits are extremely low – well below the point at which your driving would be impaired – and it’s possible to swab positive for several days after a high has worn off.

The UK government makes no apologies for this, calling it a "zero tolerance" approach rather than a "road safety" approach. The illicit drug limits have been set at the lowest possible level that rules out accidental exposure. For example, passive inhalation of marijuana smoke at a party.

How long before you're safe to drive?

So if you take drugs, how long before you’re safe to take a Drugalyser test? There’s no official advice on this. In fact, one forensic toxicologist told us “it would be irresponsible” to try to estimate when it would be safe to drive and that his best advice was “if you intend to drive, don’t do any drugs.”

The fact is, people take drugs, legal and illegal ones, in every part of the world. As somebody who recently lost a very close friend to a driver who tested positive for methamphetamine, I support any means to deter drug impaired driving. But as a realist, I think it’s important to give recreational drug users the information they need to act responsibly.

So let’s look at each illicit drug individually. But before we start, it’s important to understand that each of these figures can be affected by the size of the dose, the body mass and physical composition of the user, the user’s past usage habits, the effects of mixing drugs including alcohol, and a range of other factors that may increase or decrease detection times.

Illicit drugs

“Zero tolerance” limits

Benzoylecgonine, 50 µg/L, Cocaine, 10 µg/L

These are grouped together because benzoylecgonine is a cocaine metabolite that stays in the system slightly longer than the cocaine itself. Cocaine and its metabolite can be detected in saliva for between 2-5 days after use.

Delta–9–Tetrahydrocannabinol (Cannabis and Cannabinol), 2 µg/L

A 2-microgram limit for THC is extremely low. Marijuana use can be detected in the saliva for up to 24 hours after exposure. But it’s worth noting that it lasts much, much longer in the urine and blood. Habitual heavy users can test positive after as much as a month without the drug, as it is stored in body fat and re-released into the bloodstream when the fat is burned.

The roadside Drugalyser test will most likely only detect THC use within the last 24 hours, but any subsequent blood or urine testing may show results from 2 days to 28 days later in chronic heavy users.

Ketamine, 20 µg/L

It’s difficult to find information on how long Ketamine lasts in the system. It’s detectable in urine for up to 2 weeks, but seems to last only around 3 days in the saliva.

Lysergic Acid Diethylamide (LSD), 1 µg/L

LSD can be detected in saliva for 1-2 days after use.

Methylamphetamine - 10 µg/L

Methamphetamine can be detected in the saliva for 1-3 days after use. It’s noted in public consultation that certain types of amphetamines are used in the medical treatment of ADHD and other conditions. It’s unclear at this stage what provisions will be made for legal amphetamine users.

Methylenedioxymethaphetamine (MDMA – Ecstasy), 10 µg/L

MDMA may be detectable in the saliva for as much as 1-5 days after use.

6-Monoacetylmorphine (6-MAM – Heroin and Morphine), 5 µg/L

Heroin and morphine can be detected in the saliva for as much as 1-2 days after use.

Generally prescription drugs

“Road safety” limits

  • Clonazepam, 50 µg/L
  • Diazepam, 550 µg/L
  • Flunitrazepam, 300 µg/L
  • Lorazepam, 100 µg/L
  • Methadone, 500 µg/L
  • Morphine, 80 µg/L
  • Oxazepam, 300 µg/L
  • Temazepam, 1000 µg/L

With the illicit drugs, it’s easier to provide estimates on safe windows of usage, because the tests are looking for concentrations barely above trace levels. Unfortunately it’s much harder to provide an estimate of how much Valium or Temazepam will put you over the limit, because body physiology varies so greatly. We can only recommend users of these drugs consult with their doctors about what might constitute safe usage. And if you’re feeling any kind of effect from one of these drugs, stay off the road.

"These are very, very low limits," said Geoff Munro, National Policy Manager for the Australian Drug Foundation. "Take cocaine for example - 10 micrograms is absolutely tiny. Clearly some sort of educational campaign is essential. And there's a wider social consequence to talk about when you consider the limits for prescription drugs. Some people are probably going to have to give up driving, or stop taking their medication to stay on the road."

Perhaps the biggest trouble with any educational campaign will be that physiology differs so much person-to-person that simple rules of thumb will be almost impossible to make. The one drug most people know the most about – alcohol – is still extremely poorly understood by the general public, as our experiments with a personal breathalyser showed several years ago.

The only real way to make sure you're not running foul of the rules will be to self-test, an approach now endorsed by France, where every car now has to carry a personal breathalyser. But since Drugalyser machines cost over UK£2000, plus around UK£10 per test, and they take around 10-12 minutes, that's not going to be possible in this case.

The new testing procedures are expected to roll out later this year in England and Wales. Scotland is expected to bring forward its own drug driving legislation.

Thanks to drug testing experts Dr. Peter Lewis and Ashley Gurney. Also Darren Brien, Managing Director of the Drug Testing Institute and Geoff Monro, National Policy Manager of the Australian Drug Foundation.

About the Author
Loz Blain Loz has been one of Gizmag's most versatile contributors since 2007. Joining the team as a motorcycle specialist, he has since covered everything from medical and military technology to aeronautics, music gear and historical artefacts. Since 2010 he's branched out into photography, video and audio production, and he remains the only Gizmag contributor willing to put his name to a sex toy review. A singer by night, he's often on the road with his a cappella band Suade. All articles by Loz Blain

The British government is using road safety as an excuse for draconian drug enforcement.


Quote: "As somebody who recently lost a very close friend to a driver who tested positive for methamphetamine, I support any means to deter drug impaired driving."

While I do sympathize, I don't count someone's personal loss as legitimate justification for general legislation.

And phrases like "I support any means" send up a red flag.

Just sayin'.

"Zero tolerance" policies in the U.S. have, with few if any exceptions, been dismal failures leading to widespread gross injustice. I know you wrote people need the information to make responsible decisions, and I agree. But at the same time, irresponsible legislation is irresponsible legislation.

Anne Ominous

You're not a real pothead until you start spouting about how healthful and non-addictive it is!


As with most limits it will be Monday morning commuters barely over the limit from Saturday night who are hit hardest.


What you do not want to encourage , is someone who in the past would wait a couple of days before driving after partaking, coming to the decision that with the tolerances set it makes no difference waiting and then drives whilst still under the influence with much more dangerous likely outcomes.

Stephen Colbourne

I think the big question is, has a driver been stopped because his driving appears to be erratic, or is it a random check? I.e., has the drug affected the driver's ability to drive?

I'm sure there are a lot of accidents caused by tiredness. I have come close to this myself. On the other hand I have never taken any sorts of drugs, except alcohol. I have had no convictions for drink driving.

I would be interested to know the number of drivers who have been convicted of driving under the influence of drugs and causing an accident.

This article is the first I have heard of this new legislation, and I live in England.


We have an election coming up, so to hell with people's livelyhoods, let's show just how tough we can be. At this point all the blue rinse brigade will be sagely nodding their heads, they way they did when it was announced that young offenders would be given short sharp shock treatment. Result a whole new generation of criminals sent on 'apprenticeships' in gaols where they could learn how to burgle, steal cars and rob properly. Duh!

Of course there should be limits to drink and drug driving, but not ones where a person can lose their licence for something they did days ago and is no longer affecting their driving. That is just plain daft. I suppose when enough people have lost their licences and enough of their favourite bankers, who, incidentally, are allowed to get away with laundering drug money, have had to lean on their mates in the police and government to get their charges dropped, they will quietly alter the limits to something more realistic.

As for legislating to make cars more drug and alcohol friendly, that would be asking too much, wouldn't it? I mean, people might actually enjoy life a little, mightn't they? It would improve the economy by enticing people to go out for a meal or to see a show, so we can't have that. Can't expect politicians to realise that there is a load of technology that could be applied today to make cars much safer and save a lot more lives than this legislation ever will.

The main trouble is that most politicians are scientifically and technically illiterate. However, ask them about Plato and Socrates etc. and they will bend your ear on the subject, though it will be as irrelevant to today as it ever was.

Mel Tisdale

Anyone who has visited the UK in the last 20 years has likely encountered a drunken lout engaged in public projectile vomiting "PPV". It is disgusting and very British. Seems the pubs keep on serving until their patrons puke. Nice? No! While every country has it's drunk drivers I suspect that the UK with it's history of drinking to a stupor after work every day may be relatively unique, Russia excepted. If they also do drugs with the same regularity then that is a problem. These laws are not draconian, it is easy to avoid prosecution, don't drink or do drugs and drive...duh!

If I were king, I'd also seize their cars and sell them at auction.

Allan Bowman

Once (upon a time) there was a factory worker who was given a machine to use at work which he promptly refused to use. When asked why by his line manager he said "Well, it's difficult to get going, it leaks oil, the electrics don't work properly, you have to keep topping up the coolant, the safety guards aren't working properly, not all the panel lights work and frankly it's dangerous"

The line manager looked at him and said "Bit like your car then, but you drive that POS to work every morning and don't seem to be worried about that?"

Moral of this story is - problem goes far, far deeper than potheads and drinkers. We need zero tolerance for people who drive death traps far more than this political spin

Aloysius Bear

"But as a realist, I think it’s important to give recreational drug users the information they need to act responsibly."

Really? Aren't they already acting irresponsibly by taking illegal/legal drug for recreation? So why would we think for a moment they will act responsibly with information on how long they should wait until they can drive again when they are already breaking the law?

Here's a way to act responsibly, don't do drugs for recreational purposes. If you can't do that then do the next best thing, sell your car so you can have bus/cab/train fare to and fro.

By the way ... I also lost someone due to a driver under the influence.


Copy for the US?

Stephen Russell

I suffer chronic pain from several crushed vertebrae and am treated and monitored by a Doctor. What happens in my circumstance?


Driving isn't a right, there are other people on the road. If you want to take drugs fine, just find another way to get around. You are allowed cycle intoxicated in the UK I believe, you are allowed walk, you are allowed get a taxi, you are allowed get the train and bus.

Really there should be a zero tolerance on drink/drug driving. Only a drug user would argue, and who cares what they think, they break the law, and view road deaths as acceptable side affect of people having fun.


Agree with the zero tolerance on drink/drug driving. Found a good infographic which says that 1 in 5 Brits own up to drug driving - a shocking statistic which we need to stamp out!

David Thomson

I'm rather shocked about the whole zero tolerance thing, its all come out of the blue without even a public consultation. This is going to end up prosecuting many many people who've got high yesterday and today are no threat to road safety at all. A reasonable limit would have been acceptable, I know personally that if I get stoned it passes in a few hours and I'm OK to drive again. The govt should be trying to educate and encourage responsibility. I would favour a reduction in the blood alcohol level but not to a bloody microgram, that would be ludicrous! But that's what they have done and the reasoning entirely baffles me.

Alastair McGowan
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