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
THC clears from blood plasma with a half-life of roughly 1 to 4 days in casual users. Heavy daily users often sit closer to 4 days, and the metabolite most labs actually measure, THC-COOH, hangs on longer, with a terminal half-life somewhere in the 3 to 13 day range. A single session is usually gone from blood in a few days. A long-running daily habit can keep you detectable for a week or more.
What half-life means here
Half-life is the time it takes for the amount of drug in your blood to fall by half. THC does not follow a clean curve. Smoke or vape it and plasma levels spike within minutes, then drop fast as the drug moves into fat, muscle, and other tissue. That first plunge is redistribution, not elimination. What's left leaks back into the bloodstream slowly over days, and that slow leak is what people are quoting when they cite a half-life.
This is why you can feel sober long before a blood draw comes back clean. The high tracks the brain, not the fat stores.
The numbers worth knowing
- Peak plasma THC after smoking: usually 3 to 10 minutes
- Edibles: peak delayed 1 to 3 hours, sometimes 4, with a longer tail
- Terminal half-life of THC: about 1 to 4 days
- Terminal half-life of THC-COOH: roughly 3 to 13 days
- Single-use blood detection: typically 1 to 3 days
- Chronic heavy use: 7 days or more in blood, longer in urine
Read those as ranges from pharmacokinetic studies, not promises. The spread between individuals is wide.
Cannabis Blood Test Cutoff Levels: What the Numbers Mean
Why frequent users stay positive longer
Fat is the storage depot, and it fills up. Someone who smokes once has almost no reservoir, so clearance is quick. Someone who has smoked daily for years builds a body burden that releases back into plasma for weeks. Body fat percentage matters, and so do dose per session and potency. A 30% THC concentrate delivers far more drug than a 15% flower joint.
What shifts your number
- Frequency and dose. The largest factor by a wide margin.
- Route. Inhalation peaks high and fast. Edibles produce lower peaks but a longer exposure window.
- Body composition. More adipose tissue means more storage.
- Liver enzymes. CYP2C9 and CYP3A4 handle most THC metabolism, so genetics and liver health change the speed.
- Test cutoff. A 1 ng/mL threshold catches people a 50 ng/mL screen misses.
- Hydration and recent hard exercise. Both can nudge measured levels around.
Half-life is not impairment
A chronic user can show detectable THC in blood while completely functional. An occasional user can be impaired at a lower concentration. That mismatch is why a handful of states set per se limits around 2 to 5 ng/mL for THC or its metabolite, while others require evidence of driving behavior. A blood half-life figure is a lab concept. It does not translate into a sobriety clock.
Practical takeaway
If you have a blood draw coming and you use regularly, give yourself a week minimum and assume longer. Occasional users can usually count on 2 to 3 days. Any product or calculator that promises an exact clearance date is guessing.