A drug impaired driving charge is proven one of two ways. Either the Crown proves the drug concentration in your blood exceeded a limit set by regulation within two hours of driving, or it proves your ability to operate the vehicle was actually impaired, usually through the observations of an officer trained as a drug recognition evaluator. Nothing in either route depends on how long cannabis stays detectable in urine.
The distinction between blood concentration and urine detection causes most of the confusion about cannabis and driving. The offence measures what was in your blood while you were driving, not what a workplace screening test would still find weeks later.
The Criminal Code Sets Blood Concentration Limits by Regulation
Since 2018 the Criminal Code has contained offences based on drug concentration alone, with the limits fixed by regulation instead of in the Code itself. For cannabis there are two tiers, and the lower one is a summary conviction offence with a smaller penalty than the higher one.
A separate offence applies to a combination of alcohol and cannabis at levels below each of the individual limits. Several other drugs carry a limit expressed as any detectable amount, which means presence alone is enough.
The Offence Is Measured Within Two Hours of Driving
The concentration that matters is the one within two hours after you stopped operating the vehicle. That window exists because a sample can never be taken at the moment of driving.
It also closes the argument that a driver consumed the drug after driving instead of before. The Code allows only narrow exceptions, and they are difficult to establish.
Cannabis Metabolites in Urine Are Not Evidence of Drug Impaired Driving
Blood levels of active THC fall quickly after use, over hours rather than weeks. The inactive metabolites that a urine test detects can persist far longer, particularly in a frequent user, and they say nothing about whether the person was affected while driving.
Criminal prosecutions do not use urine metabolite testing to establish the offence. They use blood, or an evaluation, or both. Employment testing is a different exercise with different purposes, and the results are not interchangeable.
Roadside Screening for Drugs Uses Oral Fluid, Not a Breath Device
An officer who reasonably suspects a driver has a drug in their body can demand a sample of oral fluid for an approved drug screening device, or can demand that the driver perform a standardized field sobriety test at the roadside.
Both are screening tools. Neither proves the offence. A positive oral fluid result or a failed field sobriety test supplies the grounds for the next step, which is either an evaluation by a drug recognition evaluator or a demand for blood.
The Drug Recognition Evaluation Is an Opinion, and Opinions Can Be Attacked
A drug recognition evaluator conducts a structured examination at the station covering eye movements, pulse and blood pressure, muscle tone, divided attention tests and a check for injection sites. The evaluator then decides which class of drug is causing impairment, and a bodily sample is taken to confirm it.
The Supreme Court has accepted that an evaluator’s opinion can be received without qualifying the officer as an expert on each occasion, because Parliament built the qualification into the statute. The evaluation still has to be conducted correctly, in the prescribed sequence, and by a properly certified officer, and defence work on these files begins with the step-by-step record of what was done.
Blood Is Taken by a Qualified Medical Practitioner and the Chain Matters
A blood demand requires reasonable grounds and can only be executed by a qualified medical practitioner or technician who is satisfied that taking the sample will not endanger the person’s health.
From there the sample has to be sealed, stored, transported and analysed, and every hand it passes through is documented. Continuity gaps and storage problems are ordinary grounds for exclusion, which is why the disclosure request in these files is long. The disclosure chapter of the criminal process guide explains what the Crown owes you.
The Right to Counsel Applies Before the Evaluation, Not Before the Screening
Roadside screening happens immediately and the right to counsel is suspended for it. Once the driver is arrested and taken to the station for an evaluation or a blood demand, the right revives in full.
The officer must give the caution, provide access to a phone, and hold off on the evaluation until the driver has had a reasonable chance to speak to counsel. Failures at that point are among the most productive arguments available, and the right to counsel chapter sets out the standard.
Prescription and Legal Drugs Are Inside the Same Offence
Impairment by a lawfully prescribed medication is still impairment. A driver affected by opioids, sedatives or sleep aids can be charged under the same sections, and having a prescription is not a defence to impairment, though it changes the analysis on the per se limits.
The firm defends DUI charges and drug charges in New Brunswick and Nova Scotia. Read what we can do if you have been given a court date.
FAQ
Can I Refuse the Oral Fluid Test?
Refusing a lawful demand is a separate criminal offence carrying its own mandatory minimum penalty. Refusal is not a way to avoid the investigation.
How Long After Using Cannabis Is It Safe to Drive?
No lawyer can give you a number, because absorption and elimination vary between people and between products. Edibles in particular take effect slowly and last longer than smoked cannabis.
Does a Medical Cannabis Authorization Protect Me?
No. The concentration offences apply regardless of why the cannabis was consumed, and an authorization does not create an exemption.
What If the Evaluator Got the Drug Class Wrong?
That is a real line of defence. Where the toxicology does not match the evaluator’s opinion, the reliability of the whole evaluation is open to challenge.