Patrick Horan
Ireland's road traffic solicitor
How Long Do Drugs Stay in Your System for Driving in Ireland?
Cannabis, Cocaine, Codeine: How Long Before You Can Legally Drive?
“I Took It Yesterday — So I’m Grand, Right?”
That’s the sentence I hear the most in drug driving cases.
The person feels fine. They waited a day. Maybe two.
They assume they’re safe to drive.
But here’s what they don’t realise:
You can still test positive.
And if you test positive, the Gardaí can charge you.
Even if you haven’t felt high in hours, or even days.
Even if it was last night.
Even if it was “just a bit”.
Because Irish law doesn’t ask how you feel.
It asks what’s still in your system.
"The Priory Clinic in London, a leading provider of mental health and addiction services across the UK, directly quotes the website www.drugs.ie
which is managed by Ireland’s Health Services Executive (HSE)"
What the MBRS Says About Drug Detection
Let’s look at what the Medical Bureau of Road Safety (MBRS) — the body that runs all evidential drug testing in Ireland — actually says:
“Metabolites are breakdown products that are produced by the body to aid elimination of a drug through excretion. Metabolites can be active or inactive pharmacologically. The term used to describe how long a drug takes to break down in the body is called the half-life. A half-life of 1 hr means that 50% of the drug will be broken down in 1 hr, 75% at 2 hrs and so on.”
In plain English?
The drug doesn’t just disappear. It lingers.
And even if you feel fine, enough of it might still be there to tip you over the legal limit.
Drug-by-Drug: Typical Detection Windows
Here’s a rough breakdown based on published studies and clinical data.
These are estimates only, everyone processes drugs differently depending on body weight, hydration, liver function, sleep and more.
But the significance of these estimates is that seem to be both researched based and credible. In fact, the Priory Clinic in London, a leading provider of mental health and addiction services across the UK, directly quotes the website www.drugs.ie which is managed by Ireland’s Health Services Executive (HSE).
​
We can conclude that the timelines below are as accurate as possible:
Drug Detection Times for Driving in Ireland
NB: these are typical ranges, not guarantees.
"If you have a medical certificate that authorises you to use certain drugs
(eg medicinal cannabis) you may have a defence to a charge of drug driving.
But I have never seen someone in possession of such a certificate, and even if they did have one, it wouldn't protect them if they were impaired while driving"
Can You Drive If the Drug Was Taken the Night Before?
Based on the table above? It’s very doubtful. Legally it’s a minefield.
What’s interesting is that the substances tend to stay in your urine much longer than blood.
Here’s what matters:
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Was the substance still present in your blood at the time of testing?
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Was the substance on Ireland’s prohibited list?
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Were you over the threshold set by MBRS?
For drugs like cannabis, cocaine, and MDMA, the thresholds are low.
You don’t have to be impaired.
Just over the limit.
Prescription Doesn’t Mean Protection
One of the most dangerous myths is this:
“I have a prescription, so I’m allowed to drive.”
Not always true.
Yes, the law makes allowances for therapeutic use.
But if the Gardaí believe the drug impaired your driving, they can charge you.
In general though if you have a medical certificate that authorises you to use certain drugs (eg medicinal cannabis) you may have a defence to a charge of drug driving.
But I have never seen someone in possession of such a certificate, and even if they did have one, it wouldn't protect them if they were impaired while driving.
I’ve seen people prosecuted for:
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Driving under strong benzodiazepines
-
Mixing prescribed meds with alcohol
-
Using pain medication in doses that affected alertness
Even if you’re legally entitled to take the drug, you are not entitled to drive while impaired.
"Cocaine, heroin, ecstasy and methamphetamines are all far more dangerous than cannabis.
They all leave your blood from between 12 hours and 3 days. Cannabis, far less lethal, stays in your blood for up to 14 days.
And your blood is what Gardai check"
Why You Can’t Trust Online Timetables (Or AI)
Some people Google “how long does weed stay in your system” and trust the top answer.
Others ask AI tools and get confident-sounding guesses like:
“You should be fine after 12 hours.”
But here’s the reality:
Even the Medical Bureau of Road Safety (MBRS) refuses to give blanket advice.
If the MBRS — the very people who run the State lab — won’t tell you when it’s safe, why would you trust Reddit?
The Real Risk People Forget
Most people don’t get caught while high.
They get caught the next day or the next week.
On the way to work.
Or driving the kids to school.
Or doing the normal things they thought they were ready for.
And the worst part?
They test positive.
They feel normal.
But they’re at risk of losing their licence.
Key takeaway
Driving under the influence doesn’t always look like a stoned driver swerving across the road.
Sometimes it looks like a tired, well-meaning person doing the school run after a night out — with just enough THC or ketamine still in their system to land them in court.
So if you’re asking how long to wait before driving, ask yourself a better question:
Are you absolutely sure it’s gone?
"Most people don’t get caught while high. They get caught the next day or the next week.
On the way to work. Or driving the kids to school"
Because the Gardaí won’t need to guess.
They’ll just test.
And if the result comes back positive, that’s the start of a criminal prosecution.
Then you’ll need to consult good legal advice.
Cocaine, heroin, ecstasy and methamphetamines are all far more dangerous than cannabis. They all leave your blood from between 12 hours and 3 days.
Cannabis, far less lethal, stays in your blood for up to 14 days.
And your blood is what Gardai check.
After all, it’s the choice between going off the road… or driving home.
And everybody wants to drive home.