Cannabis is legal. Driving after using it is not, and the Criminal Code treats it as seriously as alcohol. Since Bill C-46 took effect in December 2018, Canada has had per se blood drug concentration limits for THC, meaning you can be charged based on a blood reading alone without police having to prove your driving was actually impaired.
The gap between what people assume and what the law says is unusually wide here. Legalization changed where you can buy cannabis; it changed nothing about driving after consuming it. Many drivers also assume a medical prescription provides some protection, or that waiting an hour or two is enough. Neither holds up. So here is what getting a DUI for driving high actually looks like in Ontario, what the THC thresholds are, and how police build these cases.
What Does Getting a DUI for Driving High Actually Involve?
Getting a DUI for driving high involves the same Criminal Code framework that applies to alcohol, prosecuted under section 320.14. Two separate routes exist: proving impairment through observation and evidence, or proving your blood drug concentration exceeded a legal threshold.
The second route is the one that changed everything in 2018. Before Bill C-46, the Crown had to establish that your ability to operate a vehicle was actually impaired, which meant proving something about your driving or your condition. The per se limits removed that burden for THC cases above the threshold. A blood reading over the line is the offence, full stop, regardless of whether you were driving perfectly.
Both routes remain available to prosecutors. Someone below the blood threshold can still face a charge of impaired operation if the evidence supports it, and someone driving flawlessly can still be charged if their blood reading exceeds the limit.
What Are the THC Driving Limits in Ontario?
Canada sets three separate THC thresholds, and which one applies determines how serious the charge is. The limits are measured in nanograms of THC per millilitre of blood, tested within two hours of driving.
The framework breaks down as follows:
- Between 2 ng and under 5 ng of THC per millilitre of blood is a straight summary conviction offence, carrying a maximum fine of $1,000 with no jail exposure
- 5 ng or more per millilitre is a hybrid offence, prosecuted the same way as an alcohol reading over 80, with the same mandatory minimum penalties
- A combination of 2.5 ng of THC per millilitre together with 50 mg of alcohol per 100 ml of blood is also a hybrid offence, capturing drivers who mixed the two at levels that would each be legal alone
That last threshold catches people who genuinely did not think they were at risk. Half the alcohol limit plus a modest amount of THC produces a full criminal charge. Anyone who has a drink and a joint at the same event is operating in that zone without realizing it.
The THC driving limit Ontario applies for young and novice drivers is different again, and stricter. Anyone under 21 or holding a G1, G2, M1, or M2 licence faces zero tolerance, meaning any detectable cannabis in their system triggers an immediate roadside suspension under provincial law.
How Do Police Prove Cannabis Impaired Driving?
Through a sequence that usually starts with observation, moves to roadside testing, and ends with a blood sample. Unlike alcohol screening, police need reasonable suspicion before they can demand a drug test.
That distinction matters. Under section 320.27(2), mandatory alcohol screening lets an officer demand a breath sample from any lawfully stopped driver with no suspicion required. Drug screening under section 320.27(1) is different: the officer must have reasonable grounds to suspect the driver has a drug in their body. Red eyes, the smell of cannabis, admissions, or observed driving behaviour typically supply that suspicion.
From there the investigation follows one of two paths. An approved oral fluid screening device, such as the Dräger DrugTest 5000 or the SoToxa, can be used at the roadside to detect recent THC use in saliva. Alternatively, an officer may administer a Standardized Field Sobriety Test, the roadside coordination assessment.
A positive result on either can support a demand for evaluation by a Drug Recognition Expert under section 320.28. The DRE evaluation is a twelve-step assessment conducted at the station by a specially trained officer, examining pulse, pupil size, muscle tone, and coordination. If the DRE concludes you are impaired by a drug, they can demand a blood sample, and that blood analysis produces the concentration figure the per se charges rest on.
Each of those steps has requirements attached, and each is a potential point of challenge. Whether the officer genuinely had reasonable suspicion, whether the screening device was properly calibrated, whether the DRE followed the prescribed protocol, and whether the blood sample was taken within the statutory window all matter.
Does a Medical Cannabis Prescription Protect You From Getting a DUI for Driving High?
No. A medical authorization gives you the legal right to possess and use cannabis. It provides no defence to impaired driving, and the same THC thresholds apply to medical users as to everyone else.
This is one of the most common and costly misunderstandings in this area. Patients using cannabis for chronic pain, anxiety, or sleep disorders often assume their prescription functions like any other medication, and that driving is fine as long as they are following their treatment plan. The Criminal Code makes no such exception.
If anything, regular medical users face a specific difficulty. Frequent cannabis use can leave detectable THC in the bloodstream longer, which means a medical patient who has not consumed for many hours may still test above 2 ng and face a summary charge. Tolerance does not lower your blood concentration; it only changes how impaired you feel.
Anyone who uses cannabis medically and needs to drive should have a direct conversation with their prescribing physician about timing and dosage. That conversation will not create a legal defence, but it may help you avoid the situation entirely.
What Are the Penalties for Cannabis Impaired Driving?
The penalties for getting a DUI for driving high mirror those for alcohol once you are above 5 ng. A first offence carries a mandatory minimum $1,000 fine and a one-year driving prohibition, with a criminal record attached.
Escalation follows the alcohol scheme exactly:
- A first offence brings the $1,000 minimum fine and a minimum one-year prohibition
- A second offence within the relevant window brings a mandatory minimum 30 days imprisonment and a two-year prohibition
- A third or subsequent offence brings a minimum 120 days imprisonment and a three-year prohibition
The provincial consequences land immediately and separately. A failed DRE evaluation triggers the 90-day Administrative Driver’s Licence Suspension, a seven-day vehicle impoundment, and a $550 penalty, all imposed at the roadside before any court involvement. Completion of the Back on Track program is required before licence reinstatement following a conviction.
One consequence deserves specific attention because it separates cannabis from alcohol. A drug-impaired driving conviction involves a controlled substance under United States federal law, which is an independent ground of inadmissibility at the American border. An alcohol-based DUI usually does not bar a Canadian from entering the US. A cannabis-based one can. We cover that difference in our guide on travelling to the US with a DUI.
How Long Should You Wait After Using Cannabis Before Driving?
There is no reliable rule, and that is the honest answer. Health Canada has not published a safe waiting period equivalent to alcohol guidance, because THC affects people too differently for a simple formula.
What is known makes the picture harder rather than easier. Inhaled cannabis produces effects that typically peak within thirty minutes and can persist for six hours or longer. Edibles behave very differently, with onset delayed by up to two hours and effects lasting twelve hours or more. Someone who ate an edible at dinner may still be impaired well into the following morning without feeling obviously affected.
Blood THC concentration and subjective impairment also do not track cleanly against each other. You can feel completely normal and still test above the threshold, particularly if you use cannabis regularly. Feeling fine is not evidence, and it is not a defence.
Frequently Asked Questions
What is the legal THC limit for driving in Canada?
Canada sets three thresholds. Between 2 ng and under 5 ng of THC per millilitre of blood is a summary offence with a maximum $1,000 fine. At 5 ng or above it becomes a hybrid offence with the same penalties as alcohol over 80. A combination of 2.5 ng THC with 50 mg of alcohol is also a hybrid offence.
Can you get a DUI for driving high with a medical prescription?
Yes. A medical cannabis authorization permits possession and use but provides no defence to impaired driving. The same blood THC thresholds apply to medical patients as to recreational users. Regular use can also leave detectable THC in the bloodstream for extended periods, increasing the risk of exceeding the limit.
How do police test for cannabis impairment in Ontario?
Police need reasonable suspicion that a driver has a drug in their body before demanding a test. They may use an approved oral fluid screening device or a Standardized Field Sobriety Test at the roadside, then a Drug Recognition Expert evaluation at the station, which can lead to a demand for a blood sample.
What are the penalties for cannabis impaired driving in Ontario?
A first offence at 5 ng or above carries a mandatory minimum $1,000 fine, a one-year driving prohibition, and a criminal record. Provincially, a failed drug evaluation triggers a 90-day licence suspension, a seven-day vehicle impoundment, and a $550 penalty imposed immediately at the roadside.
Does a cannabis DUI affect travel to the United States?
It can, more than an alcohol DUI would. A conviction involving a controlled substance is an independent ground of inadmissibility under US federal law, where cannabis remains illegal regardless of Canadian legalization. A drug-impaired conviction may bar entry where an equivalent alcohol conviction would not.
Charged With Driving High? Get the Evidence Reviewed
Cannabis impaired driving cases turn on procedure far more than most people expect. Every step, from the initial suspicion through the roadside screening, the DRE evaluation, and the blood draw, carries legal requirements that police do not always meet.
At Kazandji Law, we defend drug-impaired driving charges throughout Ontario. That means examining whether the officer had genuine reasonable suspicion to demand a test, whether the screening device was approved and properly maintained, whether the twelve-step DRE evaluation was conducted correctly, and whether the blood sample was obtained within the statutory window and analyzed properly. Getting a DUI for driving high carries consequences that reach into your licence, your record, and your ability to cross the border, so the defence deserves real scrutiny. The licence side is covered in our guide on getting your licence back after a DUI, and there is more on our criminal defence page.
Reach us at 647-588-3234 in Toronto or 647-697-5975 in Thornhill, or book a free consultation through our contact page. If you have been charged, call before your first court date so the disclosure gets reviewed properly.