Cannabis Blood Tests in Canada: What Results Can and Cannot Show
Start with what the test measured
A blood report may name delta-9-THC, a THC metabolite such as COOH-THC, or another substance. Those are not interchangeable. The result also reflects the sample collected at a particular time. Ask the testing laboratory or qualified legal counsel about the exact analyte, units, method, collection time, and report limitations.
Prior exposure is not the same as impairment
Justice Canada describes COOH-THC as the main THC metabolite. It says COOH-THC does not cause impairment and can remain in blood or urine long after impairment has resolved. Its presence can indicate previous cannabis exposure, but does not necessarily establish impairment or recent use. This statement is about that metabolite; it should not be generalized to every cannabis blood test.
Canadian driving-law context
Criminal Code s.320.14 has separate rules: operating while ability is impaired to any degree by a drug is an offence, and specified blood-drug-concentration offences apply to concentrations measured within two hours after ceasing to operate a conveyance. A statutory concentration rule is not a general clinical test for impairment, nor is a result below a threshold a declaration that driving was safe.
What this page cannot determine
This overview cannot tell whether a person was impaired at a past time, whether a particular test was reliable, whether a legal defence applies, or what a result means in a specific case. Those questions depend on exact evidence and applicable law. Preserve the report and seek case-specific advice where needed.
For a related Canadian testing question, see the Canada cannabis testing guide.
Quick FAQ
Does a positive COOH-THC result prove impairment?
No. Justice Canada says COOH-THC does not cause impairment and may persist after impairment resolves; it indicates exposure but does not necessarily show impairment or recent use.
Does any THC blood result prove when cannabis was used?
Not by itself. This page does not infer use timing from a concentration. The exact analyte, collection time, and scientific interpretation matter.
Are Canadian driving thresholds the same as an impairment diagnosis?
No. The Criminal Code includes a separate offence for operating while ability is impaired and specified concentration offences. Neither rule turns this article into an interpretation of an individual test.
Sources
- Justice Canada: Criminal Code, section 320.14
- Justice Canada: Data and implementation report, COOH-THC note
- Justice Canada: Criminal Code, section 320.31
Sources checked September 24, 2026. The Justice Canada Criminal Code page says it is current to September 3, 2026 and last amended July 18, 2026; verify later amendments. This is not an expert forensic assessment.