Understanding Cannabis Metabolite Levels in Blood
Discover how cannabis metabolites are detected in the blood and what they mean for users.
A blood test detects cannabis for about 4 to 24 hours after use, and a hair test detects it for up to 90 days. Blood measures delta-9-THC and its active metabolite at the moment of the draw. Hair captures metabolites that bind to the follicle during growth, which turns a strand into a long-term record.
Our pick: the hair test is the one that changes buying habits
If you face screening, treat the hair test as the binding constraint. It carries a 90-day memory, so it sets the rules for a full quarter rather than a weekend. A blood test clears in a day or two and rarely reshapes a long-term routine.
cannabis blood test cutoff levels
Our pick is simple: plan around the hair test, and treat the blood test as a short-term detail.
cannabis in blood vs hair test
What are the options you are comparing?
Both screens look for cannabis, but they answer different questions. One asks whether you used recently, and the other asks whether you used in the past three months.
How Long Does Cannabis Stay in Your Blood vs. Urine
- Blood test: 4 to 24 hours for occasional use, up to 2 to 7 days for heavy daily use.
- Hair test: 7 to 10 days for the strand to grow past the scalp, then up to 90 days of history in a 1.5 inch sample.
- Cost and access: a blood draw needs a phlebotomist and a lab, while a hair sample can be cut at a clinic or collected at home.
- Legal weight: blood is the standard for driving cases because it can support impairment claims, while hair is common in pre-employment and insurance screening.
How does a blood test detect cannabis?
A lab measures delta-9-THC, 11-hydroxy-THC and THC-COOH in serum or whole blood. Delta-9-THC peaks within minutes of smoking or vaping and falls fast, often below common cutoffs within a few hours. THC-COOH lingers longer, which is why heavy users can still test positive a week after their last dose.
How does a hair test detect cannabis?
Metabolites travel through the bloodstream and deposit in the follicle as the hair grows. A standard 1.5 inch sample from the scalp covers about 90 days, and body hair can extend that window. Most labs run an initial immunoassay and confirm positives with mass spectrometry.
Can external contamination cause a false hair result?
Yes, and that is the main weakness of hair testing. Smoke, handling, and contaminated surfaces can leave THC on the outside of the strand. Labs use wash steps and metabolite ratios to separate exposure from ingestion, but disputes still happen.
Which test is more accurate?
For recent use and impairment, blood is more accurate and more defensible. For long-term history, hair covers far more time but carries a higher risk of environmental false positives. Accuracy also depends on the cutoff level the lab uses, not just the specimen.
What changes the detection window?
- Frequency of use: daily users clear THC far slower than one-time users.
- Potency: high-THC concentrates and edibles raise the total body burden.
- Body fat and metabolism: THC is fat-soluble, so it releases slowly.
- Hair treatment: bleaching and dyeing can reduce, but not erase, detection.
What should you do if you buy THC products online and face a test?
Check your state and employer rules first, because testing policy varies by state and by job. If you want to keep a screen clean, the only reliable step is stopping THC long enough to clear your personal window, which can mean 90 days for hair. No detox shampoo, drink, or supplement has been proven to beat a confirmed lab result.
If you do shop online, choose brands that publish third-party lab results with potency and contaminant panels. Knowing the exact dose helps you plan, and it shows how much THC you are taking in.
Frequently asked questions
How long does THC stay in your blood?
Occasional users clear delta-9-THC within 4 to 24 hours. Chronic daily users can show THC-COOH for up to a week or more.
How long does THC stay in your hair?
About 90 days for a standard scalp sample of 1.5 inches. Body hair can hold traces longer.
Can one-time use show up in a hair test?
It can, though detection depends on dose and lab sensitivity. A single heavy session is more likely to be caught than one low-dose edible.
Is a hair test better than a blood test?
Neither is better in the abstract. Hair is better for history, and blood is better for recent use and impairment.
This is general information, not legal or medical advice. Screening rules differ by state, employer, and lab.