Short answer
Cannabis metabolites stay in blood for about 2 to 7 days after infrequent use. Heavy chronic use can extend the window to 30 days in some reports. A blood test can detect the parent drug delta-9-THC for a shorter time, often 12 to 24 hours. Labs measure 11-nor-9-carboxy-THC, the main THC metabolite, to set the window.
Can Cannabis Be Detected in Blood After 24 Hours?
What a blood test measures
A cannabis blood test looks for delta-9-THC and its metabolites. The main target is 11-nor-9-carboxy-THC, also called THC-COOH. A lab first runs an immunoassay screen. A positive screen goes to LC-MS/MS or GC-MS for confirmation. Cutoff levels vary by lab. A positive screen is not a final result.
Does Cannabis Show Up in Blood Tests After One Use?
Detection windows
- Single use: THC in blood about 12 to 24 hours. THC-COOH about 2 to 7 days.
- Use several times per week: THC-COOH about 7 to 14 days. Data vary.
- Heavy chronic use: THC-COOH up to 30 days in blood in some studies. Other reviews report 7 to 21 days. No single number fits all users.
Factors that change the window
Dose, route, frequency, body fat, liver metabolism, age, and test cutoff change detection time. Inhaled THC reaches blood in seconds. Edible THC peaks later and can stay in blood longer. Body fat stores THC and releases it over time. A lab with a low cutoff can detect metabolites for a longer period.
how long does cannabis stay in blood
CBD products and THC
CBD isolate contains no THC. Full-spectrum CBD can contain THC at 0.3% or less by dry weight under US law. Repeated use of full-spectrum CBD can produce detectable THC metabolites. Blood levels from CBD use are lower than levels from cannabis flower or concentrates. A positive blood test after CBD use is possible, but the window is shorter.
What the numbers do not show
Blood THC levels do not map to impairment for all users. A test can show past use, not current dose. Detection time is a range. A lab result depends on the test, the cutoff, and the sample. For a legal or workplace test, ask the lab for its cutoff and confirmation method.