Cannabis Metabolite in Blood: What Tests Detect and How Long It Lasts
The main cannabis metabolite in blood is THC-COOH, an inactive THC breakdown product. Learn detection windows, cutoffs, and what a positive result means.
Short answer
Most blood tests detect delta-9-THC for 1 to 6 hours after a single smoked or vaped dose. The metabolite THC-COOH lasts longer: about 1 to 2 days for occasional users and up to 7 days for heavy daily users. The exact window depends on the assay cutoff, the route of use, and how often the person uses cannabis.
Cannabis Metabolite in Blood: What Tests Detect and How Long It Lasts
Detection window by route
- Smoked flower, vape, or concentrate: parent THC peaks in plasma 5 to 10 minutes after the first puff. It stays above 1 ng/mL for about 3 to 6 hours in occasional users.
- Edibles and tinctures: peak plasma THC arrives at 1 to 3 hours. Detection lasts longer than with inhalation, often 6 to 12 hours for THC and 1 to 2 days for THC-COOH.
- Heavy daily use: THC stays above 1 ng/mL for 1 to 3 days in some users and above 0.1 ng/mL for up to 7 days in others.
What the test measures
Whole blood and plasma give different numbers. Plasma concentrations run about two times higher than whole blood. Immunoassay screens use cutoffs of 5 to 20 ng/mL. Mass spectrometry methods detect 0.1 to 1 ng/mL. A lower cutoff means a longer detection window. THC-COOH is not psychoactive. It remains in blood after delta-9-THC clears.
Factors that change the window
- Frequency of use, since chronic users clear THC from fat stores at a slower rate.
- Dose and product potency.
- Body fat percentage and metabolism.
- Assay sensitivity and cutoff concentration.
- Time between the last dose and the blood draw.
Half-life
The distribution half-life of THC in plasma is about 1 to 3 hours. The terminal half-life is longer, reported near 20 to 30 hours in chronic users. Half-life is not the same as detection window. A drug can stay detectable for several half-lives.
Limits of the evidence
Published windows come from small studies with different cutoffs, doses, and routes. No single number applies to every person. Some studies report detection past 7 days in whole blood at cutoffs of 0.1 ng/mL or lower. Blood THC concentrations also do not map cleanly to impairment. State per se limits for driving sit at 1 to 5 ng/mL in whole blood, and several states set no numeric limit at all.